JRIL
15-088
The Republic of Djibouti
DATA COLLECTION SURVEYFOR GEOTHERMAL DEVELOPMENT
IN THE REPUBLIC OF DJIBOUTI(GEOPHYSICAL SURVEY)
FINAL REPORT
AUGUST 2015
JAPAN INTERNATIONAL COOPERATION AGENCY(JICA)
NIPPON KOEI CO., LTD.
JMC GEOTHERMAL ENGINEERING CO., LTD.
SUMIKO RESOURCE EXPLORATION ANDDEVELOPMENT CO., LTD.
The Republic of Djibouti
DATA COLLECTION SURVEYFOR GEOTHERMAL DEVELOPMENT
IN THE REPUBLIC OF DJIBOUTI(GEOPHYSICAL SURVEY)
FINAL REPORT
AUGUST 2015
JAPAN INTERNATIONAL COOPERATION AGENCY(JICA)
NIPPON KOEI CO., LTD.
JMC GEOTHERMAL ENGINEERING CO., LTD.
SUMIKO RESOURCE EXPLORATION ANDDEVELOPMENT CO., LTD.
Sonalia
Gulf of Tadjoura
Eritrea
Ethiopia
Dikhil
Survey Area
Hanle Djibouti
Lac Abhe
Lac Asal
Red Sea
Arta
Obock
Gaggade
Djibouti- Awrofoul
AsalRift
Sakalol
Rouweli
Lac Abhe
Djibout
Nord Goubet
Survey Area Hanle
Hanle -1
Hanle-2
Gas Sampling Point
Garabbayis-2
Garabbayis-1 Teweo -1
Existing Test Well Tracking Record Contour (20 m)
Dug Well Fumarole Rock
Acidic Altered Rock Weaky Acidic /Propyritic altered
Legend
Survey Area
Abbreviations
ASTER Advanced Spaceborne Thermal Emission and Reflection Radiometer
CERD Centre de Recherche et des Etudes de Djibouti (Centre for the Study and
Research of Djibouti)
DEM Digital Elevation Model
EDD Electricite de Djibouti
ESIA Environmental and Social Impact Assessment
EIS Environmental Impact Statement
GENZL Geothermal Energy New Zealand Ltd.
GRMF Geothermal Risk Mitigation Facility
ICEIDA Iceland International Development Agency
IPP Independent Power Producer
ISOR Iceland Geosurvey
JICA Japan International Cooperation Agency
a.s.l Above Sea Level
MT Magneto-Telluric
NCG Non-condensable Gas
ODDEG Djiboutian Office for Development of Geothermal Energy
ORSTOM Office de la Recherche Scientifique et Technique Outre-Mer
PPP Public-Private Partnership
R gas Residual Gas
TD Total Depth
TEM Transit Electro-magnetic
TOR Terms of Reference
TVD True Vertical Depth
USAID United States Agency for International Development
WB The World Bank
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Data collection Survey for Geothermal Development in Djibouti
(Geophysical Survey)
Final Report
Executive Summary
1. Background of the Project
1.1 Background
Geothermal development has been conducted since 1970 in the Republic of Djibouti. However, geothermal
energy has not been smoothly developed partially because high salinity geothermal fluid was encountered.
Under such circumstance, the President of Djibouti requested the Prime Minister of Japan when he visited
Djibouti in August 2013 for possible technical assistance on geothermal energy development. In response
to this request, the Government of Japan expressed its intention to provide support. In accordance with this,
the Japan International Cooperation Agency (JICA) carried out the Data Collection Survey on Geothermal
Development (hereunder referred to as “JICA Survey (2014)”) in 2014 to collect and analyze geological
and geochemical information of all existing and conceived geothermal manifestation sites. As a result,
development priority was proposed.
1.2 Purposes
The purposes of the survey are as follows:
- To evaluate the geothermal resource of Hanle for consideration of possible future detailed surveys, i.e., test drilling; and
2. Review of Existing Surveys
2.1 Collected Data
The surface surveys (geological/geochemical/geophysical survey) and test well drilling had been
carried out in Hanle Region.
Based on the survey results, Aquater (1989) and Jalludin (2009) described the presence of geothermal
system in the Hanle Plain is contradicted. However, the presence of fumaroles on the plateau side
suggests the possibility of the existence of geothermal system.
Based on the existing survey results described above, the following are assumed for the geothermal
system of the Hanle Region.
1. The results of temperature distribution of the test wells indicated that a heat source causes the
fumaroles at the surface, which is believed to suggest the presence of heat source in the plateau
side. This is consistent with the fact that fumaroles are observed on the plateau.
2. The reason of low temperature of wells that have been drilled in the Hanle Plain is inferred to be
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due to the presence of groundwater flow in the Hanle Plain. In addition, hydraulic gradient
indicates the possibility that the source of groundwater is in the Hanle Plain side.
3. In the geochemical survey under the JICA Survey (2014), the possibility of a temperature of
about 250 ºC on the reservoir has been pointed out.
From the above, the presence of geothermal system may exist under the plateau that extends to the
northeast of the Hanle Plains. Therefore, the Magneto-Telluric (MT) and Transit Electro-magnetic
(TEM) surveys were performed on the plateau, in order to reveal this assumption.
3. Geophysical Survey
3.1 Objectives
In one of the target fields for geothermal development in the project, the Magneto-Telluric (MT) survey,
which is one of the electromagnetic survey methods, was conducted to study the subsurface resistivity
structure. The Transit Electro-magnetic (TEM) survey was carried out to have static correction of MT
data. The acquired data were processed and analyzed to clarify the underground resistivity structures
of the target field. The geology and geological structures were deduced from the subsurface resistivity
distribution and the geophysical information of deep zone to contribute to the creation and estimation
of geothermal reservoir model and the planning of test drilling survey was obtained.
3.2 Results of 2D Inversion
The following are the characteristics of the resistivity structure in Hanle Geothermal Field. And the
panel diagrams of resistivity cross section and plan map are shown in Figures 3-14 and 3-15,
respectively:
・ The resistivity structure consists of three zones, namely: conductive overburden, resistive
intermediate thick zone, and conductive deeper zone at a depth from the surface to -10,000 m
elevation. The resistivity distribution is roughly ranging from 1 ohm-m to 2,500 ohm-m.
・The contour line, as the boundary of 100 ohm-m resistivity between conductive overburden and
resistive intermediate zones, is located from -1,500 m to -2,000 m elevation at the southwest side of
the survey site, and its location becomes shallow to the northeast direction and is roughly ranging from
-500 m to -1,000 m elevation at the northeast side of the survey site.
・In a large sense, resistivity distribution may change from conductive to resistive from the southwest
side to the northeast side. From -1,000 m to -2,000 m elevation, the interval of contour lines is
relatively narrow. It suggests the resistivity discontinuity which shows drastic change of resistivity
value.
・The conductive overburden is thin in the graben part of the survey site and thick in the horst part
while the intermediate resistive zone shows a large value in the horst part and a small value in the
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標高100m
標高-500m
標高-1000m
標高-2000m
標高-4000m
標高-10000m
graben part of the survey site. The location of resistivity discontinuity, which shows drastic change of
resistivity, mainly coincides with the boundary between the graben and the horst.
・In all the profiles, the highest resistivity (>2,500 ohm-m) is observed from -4,000 m to -5,000 m
elevation and this high resistivity is distributed widely with a central focus on HNL200 and HNL300
profiles.
Source: The Survey Team
Figure1 Panel Diagram of Resistivity Maps 4 Supplementary Surveys
4.1 Overview of Geology and Topography
the geological and topographic feature of the survey area is as follows.
Quaternary volcanic rocks (Afar Stratoid) are widely distributed in the survey area. Major geological
layers are the lower basalt layer (2.0-2.7 Ma), upper basalt layer (1.8-2.2 Ma), and uppermost basalt
layer (1.25 is a -1.65 Ma). Rhyolite layer (1.9-2.6 Ma), which is almost the same age as the lower
basalt layer, is developed in the north.
Basalts form a plateau, covering a wide range including the MT/TEM survey area. In addition, the
uppermost basalt layer develops as volcanic corns in the NW-SE direction on the plateau.
4.2 Site Survey and Laboratory Analysis
In order to confirm the distribution of geothermal manifestations in the survey area, geological
reconnaissance was conducted in parallel with the geophysical surveys. As a result, the fumarole area
has been confirmed in the three sites around the geophysical survey area.
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The survey conducted this year is an additional survey, to study more precisely the area and chemical
change of the geothermal steam supplied. For this purpose, two fumaroles including the one surveyed
last year were examined. As a result, geothermal steam producing the geothermal manifestations can
be steadily supplied from a geothermal reservoir which has the highest temperature of 260 °C. Based
on this interpretation, it follows that Garabbayis is an appropriate location for new test drilling to
prove the presence of a geothermal reservoir.
5 Geothermal Reservoir Model and Target for Geothermal Test Wells
5.1 Preliminary Geothermal Reservoir Model
The observations/information and interpretations necessary for the construction of preliminary
geothermal reservoir model are summarized in Table1, based on the past survey results and the
geophysical survey conducted.
Table1 Summary of Observations and Interpretations
Observation Geothermal System Interpretation
Temperature at 500 m depth of the past 5 test wells increases from the plain side to the plateau side (40 ºC 90 ºC 120 ºC) Heat source The heat source may exist under the
plateau area. Fumaroles are observed only in the plateau area.
The confirmed fumaroles seem to be on the extension line of the major faults. Reservoir
Fumaroles may emerge along the faults in rhyolite and/or lower basalt layer.
The confirmed fumaroles exist on the margin of the upper basalt. Reservoir The upper basalt may act as the cap
rock of the reservoir.
The fumarole includes mantle origin gas, and the geothermometer indicates 260 ºC Fluid Fluid with high temperature may exist.
Groundwater level in the Hanle Plain is higher than that in the plateau area. Fluid recharge There may be recharging from the
plain side to the plateau side.
There is a distinct difference of resistivity structure between the plain side and the plateau side.
Regional geological structure
There may be major fault between the plain and the plateau.
Ultra high resistivity zone (1,000 Ωm or more) is identified below elevation -3,000 m in the plateau side. Heat source This may be an intrusion body that
retains high temperature.
Source: The Survey Team
Based on the above information and interpretation, the following three cases are proposed as the
preliminary geothermal reservoir model.
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Table2 Preliminary Reservoir Conceptual Models Case (a)
Figure 2 Case (b) Figure 3
Case (c) Figure 4
State of reservoir Not passed much time from the heat source intrusion High temperature reservoir is present locally
Geothermal system is fully developed Geothermal fluid circulates, and reservoir is formed over a wide range
Heat supply from the heat source is attenuated, and reservoir temperature decreases
Res
ervo
ir
Area/zone Under the plateau Along faults Along major faults only where fumaroles are confirmed
Permeability (hosted rock)
High Low Low
Temperature 260 260 260
Flu
id Origin Originated from the Hanle
Plain Originated from the Hanle
Plains Originated from the Hanle
Plain Upflow Along fractured faults Along fractured faults Along the major fault only
Heat source An intrusive rock below 3 km
Source: The Survey Team
Source: The Survey Team
Figure 2 Geothermal Conceptual Model: Case (a)
Source: The Survey Team
Figure 3 Geothermal Conceptual Model: Case (b)
SW NE
SW NE
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Source: The Survey Team
Figure 4 Geothermal Conceptual Model: Case (c) A preliminary reservoir assessment with information on the target area based on the survey shows the
following results:
Capacity (MW)
80% Most Probable 20% 16.9 32.8 86.4
5.2 Target for Geothermal Test Wells
(1) Target Position on the Map
In that zone, the locations of the most active manifestations can be a candidate for the target position
on the map, as shown by a red circle in Figure 5.
Figure 0 Map for Planning of a New Test Well Drilling in Garabbayis
(2) Target Depth
Target depth should correspond to the depth of a high temperature in the models. The altitude of the
SW NE
Source: The Survey Team
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isotherm of 250 °C is set at around -1,200 mASL in the models; thus, the target depth should be at
least 1,500 m from the surface whose altitude is ca. 300 mASL. Considering more the uncertainty of
the isotherm in the models, the target depth should be set at the depth ranging from 1,500 m to 1,800
m (-1,500 mASL) as shown in Figure 6.
Figure 6 Target Depth in the Geothermal Reservoir Model
(3) Wellhead Location
The well pad of the Garabbayis-1 well can be used for a new test well. The well pad is made of
concrete, offering a rigid and flat base for the drilling rig.
(4) Preliminary Drilling Plan
On the basis of the location of targets, preliminary drilling plan was examined. In the case where the
well pad for Garabbayis-1 is used also for the new test well, the deviation should be 300 m to reach
the farthest target. This deviation and targeted TVD (1,800 m) require a TD of 2,000 m with an
inclination of the well less than 30 °. This plan is sufficiently acceptable with a normal 2,000 m class
drilling rig.
6. Preliminary Economic Analysis for IPP Participation
With information available at this stage, the reservoir resource of the Hanle geothermal prospect was
evaluated at 15 MWe as the probable occurrence 80% that should be considered when IPP project is to
be planned. This capacity is as a similar size as of a small hydropower plant. However, the Hanle
Fault-1
Source: The Survey Team
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geothermal power station will be economically superior to the existing oil thermal power plants if the
transmission line should be constructed without financial burden to EDD.
Presently, a significant part of the electricity is being purchased from Ethiopia. Although Ethiopia still
has a large capacity of hydropower energy, the power purchase agreement between the two countries
have entered into only for a period of Ethiopia wet seasons. On the other hand, power plants within
Djiboutian territory are all of oil thermal power plant. Therefore, Djibouti does not actually have any
power plants of indigenous energy source.
Under this circumstance, constructing the Hanle geothermal power station, though the capacity is 15
MWe together with transmission line will be justifiable not only from economical point of view but
also energy security point of view too.
7. Procedure of Environmental and Social Considerations
7.1 Environmental and Social Impact Assessment Study
Decree 2011-029/PR/MHUEAT (2011) shall be referred to for the Environmental Social Impact
Assessment (ESIA), which describes the procedures to be followed. The decree classifies the
assessment into two categories: (1) basic and (2) detailed. The detailed assessment is required for test
well drilling and plan construction.
Assessment of the terms of reference (TOR) by the competent office needs about one month at least,
Survey and report preparation may take two months,
Assessment and approval of the report needs about three months, and
A total of about six months are required to start the test well drillings. 8. Proposal of Additional Surface Survey
8.1 Issues to be Solved to Realize Test Well Exploration
The following are the issues to be solved before implementation of test well exploration:
・To verify the appropriateness of the interpretation of geological structure (geological characteristics
of the Hanle Plain and the plateau).
A number of faults have been objectively confirmed by the lineament analysis using DEM data.
The MT/TEM survey identified one major fault between the Hanle Plain and the plateau.
Distribution of fracture together with regional geological structure has to be clarified.
・To improve knowledge on the characteristics of reservoirs
The resistivity structure of Hanle is different from that of a typical geothermal reservoir. Even
though, the Survey Team proposed three reservoir models based on the fact that there are
geothermal manifestations. The appropriateness of these models, however, has to be verified
with additional surface survey before test well exploration because the information at hand is
considered not to be enough to confidently propose the reservoir model which could allow more
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reliable resource estimation. The drilling target may also be refined with the additional
information.
・To understand the extent of the sheeted high resistivity zone below, and the very low resistivity zone
in the surface zone of the northeast side of the plateau
The high resistivity zone below is considered to be the heat source that would originate from
intrusive rock; and the low resistivity zone in the surface zone of the northeast side of the
plateau may form the cap structure of the reservoir. These resistivity structures extend beyond
the present MT/TEM survey area. Since these are considered to be very important to examine
the geothermal system, the survey area has to be widened. This is also important to review the
size of the reservoirs.
8.2 Proposal for Additional Survey
The following three surface surveys are proposed: (1) gravity survey, (2) additional MT/TEM survey,
and (3) micro-seismicity monitoring. In addition, the following surveys are proposed which are
necessary for smooth implementation of test well exploration in the shortest time period: (4) ESIA for
test well drilling and (5) preparatory survey for test well drilling works.
8.3 Preliminary Work Schedule Up to Test Well Drilling
A preliminary work schedule up to test well drilling is proposed in Figure 7 below.
Source: The Survey Team
Figure 7 Preliminary Work Schedule up to Test Well Drilling
9. Activities of Other Donors
9.1 USAid
- A workshop was conducted on independent power producers (IPP) and public private partnership (PPP) for the energy sector in October 2014.
- An expert was appointed in 2014 to promote IPP or PPP projects in the energy sector. It is
Work Item
1. Gravity Survey
Preparation
Observation 300 points
Analysis/Reporting
2. Microseismic Survey
Preparation
Installation 5 points
Observation 3 months
Analysis/Reporting
3. Additional MT/Tem Survey
Preparation
Observation 36 points
Analysis/Reporting
4. Comprehensive Analysis
5. ESIA
Scoping
TOR Review
Site Survey
Review
6. Preliminary Study for Test Drilling
Market Research
Civil Engineering Planning
Specification
Cost Estimation
7th 1st 2nd 3rd 4th 5th 6th
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understood that an aim of this support is to build a consensus for implementation of Power Africa under the Obama Initiative. The expert had left the country in February 2015.
- An alternative expert has been selected. The expert is not stationed in Djibouti and visits the country intermittently to conduct information collection and exchange. It is explained that the subject appears to be centered on the Asal Project in connection with investment opportunities from the country, and that specific proposals on institutional matters seem not to be made by the expert.
-
9.2 Support to Asal Geothermal Project by WB and Other Donors
- The Assal Geothermal Project is being handled by the EDD. The ODDEG and CERD serve like a technical support. Much information therefore is not available.
- Information given by ODDEG that needs to be confirmed are as follows:
The project director has been selected as of July 2015.
Procurement of drilling contractor is ongoing. The project seems to be moving.
However, every procedure has to go through the seven donors one by one, which will take a longer process.
Information on the actual implementation of drilling is yet to be made available to the Survey Team
9.3 Support from ICEIDA
The support from the Icelandic International Development Agency (ICEIDA) is categorized in the
following four sections according to the information given by ODDEG:
- Improved project management capacity for geothermal projects and project management system is in place at ODDEG (from May 2015)
- Geothermal drill training (2016)
- Improved capacity for surface exploration - Lac Abhe (from October 2015)
- Technical assistance (finalization of Geothermal Risk Mitigation Facility (GRMF) application and other matters, as applicable)
ICEIDA supported ODDEG in the preparation of the application to GRMF for the surface survey in
Nord Goubet. Although the expression of interest (EoI) was accepted, the preparation of the full
application was suspended.
9.4 GRMF
The ODDEG submitted the full application to GRMF for the surface survey of Arta geothermal
prospect with the assistance of a Japanese consultant group. The result will be notified by GRMF by
January 2016. If the application is accepted, the surface survey will be conducted by the staff of
ODDEG with the technical advice of the Japanese consultant group.
10. Activities with the National Fund
The Government of Djibouti is now in the process of procuring a drilling rig from Turkey. The present
conditions are as follows:
- Contract negotiation for purchasing a drilling rig with 2,000 m capacity. The machine would be
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made available in Djibouti in 2017.
- A second-hand drilling rig with 900 m capacity will be provided from Turkish company, and will be made available in Djibouti in the coming September 2015. The ODDEG intends to conduct training of their staff with this machine.
- Information is yet to be made available to the Survey Team on how these rigs are to be operated when the Asal Project or other projects are to be implemented.
11. Conclusions and Recommendations
11.1 Conclusions
【 Geothermal Resource Assessment】
(1) The Hanle Plain has a main fault in its northwest plateau.
(2) The heat source and geothermal reservoir exist underneath the northwest plateau.
(3) The resistivity structures obtained by the geophysical survey do not show a similar pattern to the
typical geothermal resistivity structure of a geothermal reservoir. This is the reason why it is
considered that the hydrothermal alteration is not yet well advanced in Hanle.
(4) However, the Survey Team considers the geothermal system, which represents that manifestations
in field should consist of the heat source, reservoir, and fluid.
・ Heat source should be a body that shows high resistivity and is considered to be an intrusion
body.
・ Reservoir should be fractured faults themselves or together with permeable layers in the
lower basalt, with capping structure made up of upper basalt. The reservoir could be 260 °C
according to the geochemical survey that the Survey Team conducted.
・ Geothermal fluid should be recharged from the Hanle Plain where groundwater level is
higher than in the plateau.
(5) A preliminary reservoir assessment with information on the target area based on the survey shows
the following results:
Capacity (MW)
80% Most Probable 20%
16.9 32.8 86.4
However, there will be issues that need to be clarified as described in Section 11.2 below, and this
preliminary estimation shall be reviewed through the clarification of these issues.
【Environmental and Social Impact Assessment (ESIA)】
An ESIA is required by the Government of Djibouti before implementation of test well drillings as
well as before construction of geothermal plant. The process from the application with TOR to the
approval of ESIA for drilling works will need at least six months. To facilitate the implementation of
the works, the Survey Team has prepared the proposed TOR based on the one for the geothermal
development project in Asal, which is now in the process of project implementation.
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【Preliminary Economic Analysis Assuming IPP Project】
The ODDEG intends to invite an IPP to the Hanle geothermal prospect after the geothermal resources
are confirmed by test wells, in principle. The Survey Team conducted a preliminary economic
assessment of a 15 MW geothermal power plant operated by an IPP which resulted in a breakeven
tariff of US$12.96/kWh for the power plant as against the estimated levelized cost of electricity
(LCOE) of US$19.0/kWh of a diesel power plant as an alternative case.
Although the breakeven tariff is higher than the energy price imported from the Ethiopia Hydropower
System, the Survey Team considered that the estimated breakeven price of the 15 MW geothermal
power project would be attractive for EDD taking into account energy security. Thus, an IPP project in
Hanle would be a promising option.
11.2 Issues and Recommendations
【Reservoir Estimation and Decision for Test Well Drilling】
Issues:
The next step after the geophysical survey would be the test well drilling based on a standard project
sequence. However, the resistivity structure of the Hanle Reservoir has been revealed to be different
from the typical resistivity structure. On the other hand, the Survey Team considered the need to have
a geothermal reservoir because clear and strong geothermal manifestations are observed on site. The
Survey Team considers it prudent and necessary to conduct the additional 3-G survey which will
contribute to the clarity of the geothermal system. With these information, a decision of ‘Go’ or
‘No-go’ for test well drilling could be made.
Recommendations:
The following additional surveys have been proposed in this report:
Gravity survey for consideration of geological structure in connection with geothermal reservoir system,
Additional MT/TEM survey for identification of the possible extent of geothermal reservoir,
3D inversion analysis for MT/TEM data, and
Micro-seismicity monitoring for identification of geothermal fluid movement.
【Environmental and Social Impact Assessment ESIA】
Issues
An ESIA process for test well drilling will need at least six months, which may retard the process of a
speedy development.
Recommendations:
It is recommended to conduct such process together with the proposed additional 3-G survey in order
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to implement the test well drilling immediately after the additional 3-G survey.
【Survey on Procurement for Drilling Works】
Issues
Djibouti has experiences in conducting test well in the 1980s. but since then, the activities were
suspended. There is actually few information regarding availability of drilling machines, drilling
contractors, and modes of contract together with cost information.
Recommendations:
It is therefore necessary to conduct a survey on procurement matters for the drilling works.
【Preliminary Economic Analysis for an IPP Project】
Issues
The ODDEG intends to invite an IPP for the Hanle geothermal prospect after the confirmation of
geothermal resources. This report conducted a preliminary economic analysis focusing on IPP project
through desk study with available information at hand. The results of this analysis should be refined
with the information on economic factors as well as the results or reassessment of geothermal resource
with additional information to be obtained from the additional 3-G survey.
Recommendations:
It is recommended to conduct a preliminary economic assessment assuming an IPP project that the
ODDEG intends to introduce.
*** end of report **
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DATA COLLECTION SURVEY
FOR GEOTHERMAL DEVELOPMENT IN DJIBOUTI
(GEOPHYSICAL SURVEY)
FINAL REPORT
Table of Content
Location Map
Abbreviations
Summary
Chapter 1 Background of the Project ..................................................................................................... 1-1
1.1 Background ............................................................................................................................... 1-1
1.2 Purpose and Scope .................................................................................................................... 1-2
1.2.1 Purposes ............................................................................................................................ 1-2
1.2.2 Survey Areas ..................................................................................................................... 1-2
1.2.3 Scope ................................................................................................................................. 1-2
Chapter 2 Review of Existing Surveys .................................................................................................. 2-1
2.1 Collected Data ........................................................................................................................... 2-1
2.2 Surface Survey .......................................................................................................................... 2-1
2.2.1 Geological and Geochemical Survey ................................................................................ 2-1
2.3 Drilling Data of Existing Wells ................................................................................................ 2-4
2.3.1 Overview ........................................................................................................................... 2-4
2.3.2 Geological Structure ......................................................................................................... 2-6
2.3.3 Alteration Minerals ........................................................................................................... 2-6
2.3.4 Distribution of Permeability .............................................................................................. 2-7
2.3.5 Wellbore Temperature ...................................................................................................... 2-7
2.4 Summary of Existing Surveys ................................................................................................... 2-9
2.4.1 Conclusion of Existing Survey ......................................................................................... 2-9
2.4.2 Interpretation of the Survey Team .................................................................................... 2-9
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Chapter 3 Geophysical Survey .............................................................................................................. 3-1
3.1 Objectives ................................................................................................................................. 3-1
3.2 Survey Results .......................................................................................................................... 3-1
3.2.1 Outline of Survey .............................................................................................................. 3-1
3.2.2 Results of Survey .............................................................................................................. 3-2
3.2.3 Results of 2D Inversion ..................................................................................................... 3-2
3.2.4 Conclusions of 2D Inversion ............................................................................................. 3-5
Chapter 4 Supplementary Surveys......................................................................................................... 4-1
4.1 Overview of Geology and Topography ..................................................................................... 4-1
4.1.1 Geological Structure ......................................................................................................... 4-1
4.1.2 Fault Distribution .............................................................................................................. 4-1
4.2 Site Survey and Laboratory Analysis ........................................................................................ 4-4
4.2.1 Surface Manifestation ....................................................................................................... 4-4
4.2.2 Geochemical Survey ......................................................................................................... 4-6
Chapter 5 Geothermal Reservoir Model and Target for Geothermal Test Wells .................................. 5-1
5.1 Construction of Conceptual Model ........................................................................................... 5-1
5.1.1 Geothermal Reservoir and Resistivity Structure ............................................................... 5-1
5.1.2 Resistivity Structure of Hanle Site .................................................................................... 5-2
5.1.3 Preliminary Geothermal Reservoir Model ........................................................................ 5-3
5.1.4 Preliminary Evaluation of Geothermal Potential .............................................................. 5-8
5.2 Target for Geothermal Test Wells .......................................................................................... 5-10
Chapter 6 Preliminary Economic Analysis for IPP Participation .......................................................... 6-1
6.1 Assumptions .............................................................................................................................. 6-1
6.2 IPP Breakeven Power Sales Prices at the Power Station .......................................................... 6-1
6.3 Transmission Cost ..................................................................................................................... 6-2
6.4 Power Purchasing Cost at Ali Sabieh Substation. ..................................................................... 6-2
6.5 A comparison with the power generation cost at the existing power plants ............................. 6-3
6.6 Conclusions ............................................................................................................................... 6-3
Chapter 7 Procedure of Environmental and Social Considerations ....................................................... 7-1
7.1 Environmental and Social Impact Assessment Study ............................................................... 7-1
7.2 Review of Existing Surveys(ESIA for Asal Geothermal Project) ....................................... 7-2
7.3 Draft Terms of Reference ......................................................................................................... 7-2
Chapter 8 Proposal for Additional Surface Survey ............................................................................... 8-1
8.1 Issues to be Solved to Realize Test Well Exploration .............................................................. 8-1
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8.2 Proposal for Additional Survey ................................................................................................. 8-2
8.3 Preliminary Work Schedule up to Test Well Drilling ............................................................... 8-6
Chapter 9 Activities of Other Donors .................................................................................................... 9-1
9.1 United States Agency for International Aid (USAID) .............................................................. 9-1
9.2 Support to Asal Geothermal Project by the World Bank (WB) and Other Donors .................. 9-1
9.3 Support from ICEIDA ............................................................................................................... 9-1
9.4 Geothermal Risk Mitigation Facility (GRMF) ......................................................................... 9-2
Chapter 10 Activities with National Fund ............................................................................................. 10-1
10.1 Procurement of Drilling Machines .......................................................................................... 10-1
10.2 Construction of the New ODDEG Office at PK 12 ................................................................ 10-1
Chapter 11 Conclusions and Recommendations ................................................................................... 11-1
11.1 Conclusions ............................................................................................................................. 11-1
11.2 Issues and Recommendations ................................................................................................. 11-2
Figures and Tables
Table 1-1 Proposed Development Priority in JICA Survey (2014) ............................................... 1-1
Table 2-1 Existing Information ...................................................................................................... 2-1
Table 2-2 Data of Existing Wells ................................................................................................... 2-5
Table 2-3 List of Aquifer Depth .................................................................................................... 2-7
Table 4-1 List of Geothermal Manifestation .................................................................................. 4-4
Table 4-2 Results of the Chemical Analysis for Fumarolic Gas in Garabbayis ............................. 4-8
Table 5-1 Relation between Resistivity and Alteration Minerals and Temperature ...................... 5-1
Table 5-3 Summary of Observations and Interpretations .............................................................. 5-3
Table 5-4 Preliminary Reservoir Conceptual Models .................................................................... 5-4
Table 5-5 Parameters for the Volumetric Method ......................................................................... 5-9
Table 5-6 Preliminary Resource Assessment ................................................................................. 5-9
Table 6.1 Assumptions for Examination of IPP Breakeven Power Price ......................................... 6-1
Table 6.2 IPP Breakeven Power Sales Prices Sold-out at the Hanle Geothermal Power Station .. 6-2
Table 6.3 Assumptions for Transmission Cost Calculation ........................................................... 6-2
Table 6.4 Power Purchasing Cost at the Ali Sabieh Substation ..................................................... 6-3
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Figure 1-1 Geothermal Development Stages ................................................................................. 1-2
Figure 2-1 Fluid Circulation in the Hanle Plains based on Geochemical Analysis ....................... 2-2
Figure 2-2 Fluid Flow System of Fumaroles ................................................................................. 2-2
Figure 2-3 Location Map of Electrical Survey in Hanle Plains ..................................................... 2-3
Figure 2-4 Results of Electrical Survey and Interpretation ............................................................ 2-4
Figure 2-5 Location Map of the Existing Wells ............................................................................. 2-5
Figure 2-6 Distribution Chart of Altered Minerals ........................................................................ 2-7
Figure 2-7 Contour Map of Underground Temperature(- 500 m a.s.l) ..................................... 2-8
Figure 2-8 Temperature Profiles in the Existing Wells .................................................................. 2-8
Figure 3-1 Location Map of MT Survey Site ................................................................................. 3-6
Figure 3-2 Location Map of MT Stations ...................................................................................... 3-7
Figure 3-3 Resistivity Cross Section (HNL100) ............................................................................ 3-8
Figure 3-4 Resistivity Cross Section (HNL200) ............................................................................ 3-9
Figure 3-5 Resistivity Cross Section (HNL300) .......................................................................... 3-10
Figure 3-6 Resistivity Cross Section (HNL400) .......................................................................... 3-11
Figure 3-7 Resistivity Cross Section (HNL500) .......................................................................... 3-12
Figure 3-8 Resistivity Plan Map (-100 m elevation) .................................................................... 3-13
Figure 3-9 Resistivity Plan Map (-500 m elevation) .................................................................... 3-13
Figure 3-10 Resistivity Plan Map (-1,000 m elevation) ............................................................... 3-14
Figure 3-11 Resistivity Plan Map (-2,000 m elevation) ............................................................... 3-14
Figure 3-12 Resistivity Plan Map (-4,000 m elevation) ............................................................... 3-15
Figure 3-13 Resistivity Plan Map (-10,000 m elevation) ............................................................. 3-15
Figure 3-14 Panel Diagram of Resistivity Plan Maps .................................................................. 3-16
Figure 3-15 Panel Diagram of Resistivity Plan Maps .................................................................. 3-17
Figure 4-1 Geological Map of the Survey Area ............................................................................. 4-1
Figure 4-2 Inclination Distribution Map and Inclination Direction Map ....................................... 4-2
Figure 4-3 Fault Distribution Map ................................................................................................. 4-3
Figure 4-5 Location Map of Geothermal Manifestation ................................................................ 4-4
Figure 4-6 Distribution Map of Geothermal Manifestation ........................................................... 4-5
Figure 4-7 Geochemical Survey Area ............................................................................................ 4-6
Figure 4-8 Photographs of Geothermal Manifestations in Garabbayis .......................................... 4-7
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Figure 4-9 He-Ar-N2 Ternary Diagram for Garabbayis Fumarolic Gases ..................................... 4-9
Figure 5-1 Geothermal Reservoir and Resistivity Structure .......................................................... 5-1
Figure 5-2 Resistivity and Alteration Mineral ............................................................................... 5-3
Figure 5-3 Geothermal Conceptual Model: Case (a) ..................................................................... 5-5
Figure 5-4 Geothermal Conceptual Model: Case (b) ..................................................................... 5-6
Figure 5-5 Geothermal Conceptual Model: Case (c) ..................................................................... 5-7
Figure 5-6 Map for Planning of a New Test Well Drilling in Garabbayis ................................... 5-10
Figure 5-7 Target Depth in the Geothermal Reservoir Model ..................................................... 5-11
Figure 7-1 ESIA Procedures .......................................................................................................... 7-1
Appendices
Appendix -1 List of Collected Documents
Appendix -2 Record Photographs
Appendix -3 Data of Existing Wells
Appendix -4 Geophysical Survey
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Chapter 1 Background of the Project
1.1 Background
Geothermal development has been conducted since 1970 in the Republic of Djibouti.
However, geothermal energy has not been smoothly developed partially because high
salinity geothermal fluid was encountered. Under such circumstance, the President of
Djibouti requested the Prime Minister of Japan when he visited Djibouti in August 2013 for
possible technical assistance on geothermal energy development. In response to this request,
the Government of Japan expressed its intention to provide support. In accordance with this,
the Japan International Cooperation Agency (JICA) carried out the Data Collection Survey
on Geothermal Development (hereunder referred to as “JICA Survey (2014)”) in 2014 to
collect and analyze geological and geochemical information of all existing and conceived
geothermal manifestation sites. As a result, development priority was proposed as shown in
Table 1-1.
Table 1-1 Proposed Development Priority in JICA Survey (2014)
Site Name
Geothermal Resources Workability Socio-Environmen (Reference)
Priority
Survey for the Next Stage
Others
Re- sources
CL (mg/L)
Accessi- bility Landform
Well DrillingWater
NaturalConditions
Inha-bitant
Distance to
ransmissio
DjiboutianPriority
Hanle A A
±1,000 C
B Plain-
ragged hill
A GroundwaterIn Hanle Plain
A Barren
A None
45 km to Dikhil
2 1 MT Survey
Arta A D
>30,000 B
B Plain-
ragged hill
C Sea
A Barren
B A few
6 km to N.1
4 2 MT Survey
Applicationpending
for GRMF
Nord Goubet A
D >30,000
C-D C
Plain- ragged hill
C Sea
A Barren
B A few
50 km to P.K. 51
1 2 Review ofCERD’s
MT Survey
Applicationpending
for GRMF
Gaggade A B
<5,000 D
D Ragged hill
A GroundwaterIn Hanle Plain
A barren
A None
40 km to P.K 51
2 3 MT Survey
Obock B C
10,000~20,000
A A
Plain C
Sea B
Coastal
D NearTown
Isolated 3 4 Review ofCERD’s
MT Survey
Djibouti- Awrofoul C
A ±1,000
A A
Plain C
Sea - - - - 5 MT Survey
A:Excellent, B:Good, C:Fair, D:Poor Source: The Survey Team
There are seven stages in geothermal development in general. Among these seven, the JICA Survey
(2014) corresponds to the “Surface Survey Stage” (Figure 1.1). In order to proceed to the “Test
Drilling” stage, it is necessary to select/identify drilling targets by detailed surface surveys
(geophysical survey followed by construction of geothermal conceptual model). Under this
circumstance, the JICA Survey (2014) (geophysical survey) has thus been instigated by JICA.
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Source: The Survey Team
Figure 1-1 Geothermal Development Stages
1.2 Purpose and Scope
1.2.1 Purposes
The purposes of the survey are as follows:
- To evaluate the geothermal resource of Hanle for consideration of possible future detailed surveys, i.e., test drilling; and
- To assess the requirement for environmental assessment for drilling and future plant construction.
1.2.2 Survey Areas
Hanle Garabbayis, Republic of Djibouti
The survey location is shown after the cover page.
1.2.3 Scope
The scope of work of the survey is as follows:
① To implement geophysical survey,
② To evaluate the geothermal resource through construction of a conceptual geothermal model
of Hanle’s geothermal prospect,
③ To assess the necessity of test well drilling, and
④ To select drilling targets.
Next SurveyGeological, Geochemical and Geophysical Surveys
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Chapter 2 Review of Existing Surveys
2.1 Collected Data
The existing surveys that had been carried out in Hanle Region are shown in Table 2-1.
Table 2-1 Existing Information No Name Author Year Geo-
logy Geo-
chemistry Geo-
physicsDrilling
1 PROJET POUR L’EVALUATION DES RESSOURCES GEOTHERMIQUES
Aquater 1981
2 RESSOURCES GEOTHERMIQUES ETUDES EFFECTUEES PAR AQUATER 1980 - 1982
Aquater 1982
3 INTERPRETATION OF GRADIENT WELLS DATA – HANLE PLAIN
Geotermica 1985
4 GEOTHERMAL EXPLORATION PROJECT HANLE-GAGGADE REPUBLIC OF DJIBOUTI – HANLE 1 REPORT
Aquater 1987 a
5 GEOTHERMAL EXPLORATION PROJECT HANLE-GAGGADE REPUBLIC OF DJIBOUTI – HANLE 2 REPORT
Aquater 1987 b
6 CARTE GEOLOGIQUE DE LA REPUBLIQUE DE DJIBOUTI A 1:100000 - DIKHIL
ORSTOM 1987
7 DJIBOUTI GEOTHERMAL EXPLORATION PROJECT REPUBLIC OF DJIBOUTI – DRAFT FINAL REPORT
Aquater 1989
8 DATA COLLECTION SURVEY ON GEOTHERMAL DEVELOPMENT IN THE REPUBLIC OF DJIBOUTI
JICA 2014
Source: The Survey Team
2.2 Surface Survey
2.2.1 Geological and Geochemical Survey
Based on Aquater (1981), geological and geochemical survey was carried out in the Hanle Plains. About 22 rock samples were collected, observed, and analyzed. In the geochemical survey, hot spring water, spring water, and fumarolic gas were collected and analyzed.
As a result, it indicated the presence of three aquifers, namely: sedimentary rock (chlorinated alkaline water), alluvial aquifer (bicarbonate-alkaline earth water), and volcanic aquifer (bicarbonate-alkaline sulphate chlorinated water) (Figure 2-1). Also, the upflow of fluid containing CO2 from deep underground was suggested. The model shown in Figure 2-2 was proposed for the source of fumarole.
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Source: Modified from Aquater (1981)
Figure 2-1 Fluid Circulation in the Hanle Plains based on Geochemical Analysis
Source: Modified from Aquater (1982)
Figure 2-2 Fluid Flow System of Fumaroles
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In Hanle Region, electrical survey was carried out in the entire Hanle Plains by Aquater (1982). The
survey point arrangement is shown in Figure 2-3; the fumarole points that have been confirmed by the
JICA Survey (2014) are located at the southeast end of the survey area.
The analysis result of the resistivity cross section (NE-SW direction) is shown in Figure 2-4. Low
resistivity layer in the shallow part (a few Ωm) and high resistivity layer in the deep part (tens Ωm) are
confirmed, and it was concluded that each of these parts corresponds to sedimentary/alluvium layer and
volcanic rock layer, respectively. Discontinuity of resistivity structure was confirmed in the center of the
Hanle Plains, which suggests fault structure. The exploration well drilling was proposed to aim at these
faults.
Source: Modified from Aquater (1982)
Figure 2-3 Location Map of Electrical Survey in Hanle Plains
Survey Area
Cross-section of Figure 2-4
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Source: Modified from Aquater (1982)
Figure 2-4 Results of Electrical Survey and Interpretation
2.3 Drilling Data of Existing Wells
2.3.1 Overview
In Hanle Region, five wells were drilled in the 1980s. These wells were drilled on the plain area
according to the results of surface survey described in the previous section (Figure 2-5). Table 2-2
shows the main data of existing wells.
Garabbayis-1, Garabbayis-2, and Teweo-1 are structural drilling wells about 450 m deep to assess the
underground temperature. The results of these exploration wells were presented in Aquater (1982) and
Geotermica (1985). Deep exploration wells Hanle-1 (drilling depth of 1,623.8 m) and Hanle-2 (drilling
depth of 2,038 m) were carried out to reflect the results of the structural drilling wells. These results
were reported in Aquater (1987 a, b; 1989).
Alluvium
Volcanic Rock
Geological Interpretation
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Table 2-2 Data of Existing Wells Item Well Name
Garabbayis-1 Garabbayis-2 Teweo-1 Hanle-1 Hanle-2 Coordinate N11º24’26.0”
E42º10’44.3”
Elevation : 299m
N11º24’17.5”
E42º10’06.0”
Elevation : 245m
N11º26’36.2”
E42º05’11.9”
Elevation :142m
N11º26’33.0”
E42º07’26.0”
Elevation :210m
N11º24’07.1”
E42º09’54.7”
Elevation: 236.8m
Depth 437m 452.2 m 452 m 1623.8 m 2038 m Drilling Period 1982
(Period is unknown)
1984/11/9 –
1984/11/28
(20days)
1984/10/30 –
1984/11/08, 1984/11/29 –
1984/12/15
(27days)
1987/01/02 –
1987/03/02
(32days)
1987/03/11 –
1987/04/23
(44days)
Well Diameter (Bottom)
5-5/8” 5-7/8” 5-7/8” 8-1/2” 8-1/2”
Temperature at Bottom hole ()
121.7 80.8 43.7 72 122.7
Contractor Genie Rural* GENZL GENZL INTAIRDRIL INTAIRDRIL *Now called Direction de l’eau Source: Compiled by the Survey Team
Source: The Survey Team
Figure 2-5 Location Map of the Existing Wells
Garabbayis-1
Teweo-1 Hanle-1
Hanle-2
Garabbayis-2
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The features of the existing wells are discussed below.
2.3.2 Geological Structure
The features that can be deduced from the geological data are as follows:
In the exploration well, basalt layer has thick distribution.
In Teweo-1 and Hanle-1, the rhyolite layer appeared between the basalt layers. Distribution depth is as follows: Teweo-1: 257-278 m, Hanle-1: 98-220 m, 230-310 m, 610-680 m.
Alluvium was confirmed in the surface portion of Teweo-1, Hanle-1, and Hanle-2.
Mudstone layer was confirmed on Teweo-1 at the depth of 65 m-257 m.
The geological column of each exploration well is attached.
2.3.3 Alteration Minerals
The alteration minerals occurrence depth in each exploration well is shown in Figure 2-6.
Documentation indicating the alteration mineral occurrence for Garabbayis-1 was not available.
As a feature of the whole alteration minerals, low-grade alteration is observed characterized by
occurrence of zeolites. The following issues are presumed by the combination of alteration mineral
occurrence;
The transition zone between heulandite (He) – laumontite (Lm) is located at GL-1400m in Hanle-1, GL-1000m at Hanle-2, presumed that the zone was approximately 140 degrees of alteration environment.
Smectite is disappeared and chlorite is commonly observed at the depth of 1400m in hanle-2, presumed that the alteration environment is 180 to 200 degrees.
Epidote (EP) and Hematite (Hm) is observed at the limited depth of 200m and 300m. The appearance temperature of those minerals are approximately 200 degrees, therefore those minerals are originated by vein-let hydrothermal alteration.
Pyrite is intermittently observed at the depth from GL-1000m to 1900m, indicates hydrothermal alteration caused by acidic fluid.
Occurrence of zeolite and chlorite is described, but the detail is not identified in Garabbayis-2 and Teweo-1, indicates that the data may not be reliable.
Combination of alteration minerals deeper than the depth of GL-1500m may indicate more than 200
degrees of alteration environment.
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Source: Compiled from Geotermica (1985) and Aquater(1989)
Figure 2-6 Distribution Chart of Altered Minerals
2.3.4 Distribution of Permeability
On each exploration well, the depths of high permeability and presence of aquifer are shown in Table
2-3. The aquifer is observed at depths of 80-90 m, 130-200 m, and 250-350 m in the shallow part for
several wells. This indicates that the aquifer is continuous in the horizontal direction. In the deeper
part (deeper than 1,000 m), an aquifer was only identified at the depth of 1,300 m in Hanle-1, and was
supposed to low permeability (Aquater (1987 b)). But because deep well was drilled only two sites,
this fact is not enough to conclude the permeability of Hanle area is low.
In addition, the groundwater levels of Garabbayis-1, Garabbayis-2, and Teweo-1 observed in December
1984 were 113 m, 60 m, and 17 m, respectively. This indicates a decrease of groundwater level in the
direction from the plain side to the plateau side.
Table 2-3 List of Aquifer Depth Garabbayis-1 Garabbayis-2 Teweo-1 Hanle-1 Hanle-2
Shallower than 1000 m
83 m 95 m 150 m 180 m
90 m 130 m 364 m
95 m 130-200 m
310 m 680-800 m
140-170 m 260 m 405 m
Deeper than 1000 m
- - - About 1300 m -
Source: The Survey Team
2.3.5 Wellbore Temperature
Figure 2-7 shows the temperature contour in -500 m a.s.l, which is assumed from the confirmed
underground temperature distribution in each well. It was assumed to be consistent with the structure of
NNW-SSE. It is confirmed that there is a tendency of temperature increase from the Hanle Plain side to
the plateau side. The underground temperature distribution of each well is summarized in Figure 2-8.
Si Hm Ch Ze Si Hm Qz Ze Ep Cc Sm Si Ch Qz He Lm Cc Sm Si Py Ch Qz He Lm
Cc Ch Ep He Hm Lm Py Qz
Si Sm Ze
Pyrite Quartz
SiO2 Smectite Zeolite
Calcite Chlorite Epidote Heulandite Hematite Laumontite
DepthGarabbayis-2 Teweo-1 Hanle-1 Hanle-2
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
1600
1700
1800
1900
2000
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Source: The Survey Team
Figure 2-7 Contour Map of Underground Temperature(- 500 m a.s.l)
Source: Modified from Aquater (1989)
Figure 2-8 Temperature Profiles in the Existing Wells
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2.4 Summary of Existing Surveys
2.4.1 Conclusion of Existing Survey
Based on the survey results, Aquater (1989) described the following conclusions:
The Hanle Plains can be characterized as a low temperature system where the temperature is controlled by groundwater circulation.
The zone with an almost constant temperature from about 400 m to 1,000 m in Hanle-2 could be related to the local thermal anomaly originated by the upflow of hot fluids at the Garabbayis fumaroles.
The possibility of finding high enthalpy fluids for electric power generation within the Hanle Plains was very low.
In addition, Jalludin (2009) concluded the following:
Any shallow thermal anomalies related to intrusions or magma chamber do not exist in the Hanle Plain.
The fumaroles of Garabbayis would represent an exceptional situation, where the major fault system is connected to some very deep thermal anomalies.
From the results of existing studies, the presence of geothermal system in the Hanle Plain is
contradicted. However, the presence of fumaroles on the plateau side suggests the possibility of the
existence of geothermal system.
2.4.2 Interpretation of the Survey Team
Based on the existing survey results described above, the following are assumed for the geothermal
system of the Hanle Region.
1. As to the results of test well drilling, temperature of the deep part of Hanle Plain is low and the
wells located in the northeastern part of the plain have slightly higher temperature (Figure 2-7).
2. The results of temperature distribution of the test wells indicated that a heat source causes the
fumaroles at the surface, which is believed to suggest the presence of heat source in the plateau
side. This is consistent with the fact that fumaroles are observed on the plateau.
3. The reason of low temperature of wells that have been drilled in the Hanle Plain is inferred to be
due to the presence of groundwater flow in the Hanle Plain. In addition, hydraulic gradient
indicates the possibility that the source of groundwater is in the Hanle Plain side.
4. In the geochemical survey under the JICA Survey (2014), the possibility of a temperature of about
250 ºC on the reservoir has been pointed out.
From the above, the presence of geothermal system may exist under the plateau that extends to the
northeast of the Hanle Plains. Therefore, the Magneto-Telluric (MT) and Transit Electro-magnetic
(TEM) surveys were performed on the plateau, in order to reveal this assumption.
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Chapter 3 Geophysical Survey
3.1 Objectives
In one of the target fields for geothermal development in the project, the Magneto-Telluric (MT) survey,
which is one of the electromagnetic survey methods, was conducted to study the subsurface resistivity
structure. The Transit Electro-magnetic (TEM) survey was carried out to have static correction of MT
data. The acquired data were processed and analyzed to clarify the underground resistivity structures of
the target field. The geology and geological structures were deduced from the subsurface resistivity
distribution and the geophysical information of deep zone to contribute to the creation and estimation of
geothermal reservoir model and the planning of test drilling survey was obtained.
3.2 Survey Results
3.2.1 Outline of Survey
The following are the contents of MT survey and TEM survey carried out in the project. The location
map and stations map of MT and TEM surveys are shown in Figures 3-1 and 3-2, respectively. The list
of the coordinate system of the stations is at the back of the report.
・Survey Method
MT method with far remote reference site
TEM method with central loop system(for static correction of MT data)
・Survey Site
The survey area was decided by referring to the existing geological information and well drilling exploration. In this survey, the deployment of MT/TEM stations was decided with a central focus on the horst where manifestations of fumaroles are observed in the northeast part of Hanle Plateau.
・Operation Date
March 28, 2015 ~ May 5, 2015
・Number of Stations
30 stations, Remote reference station in Dikhil
・Acquired Data
MT method: Three components of magnetic field (Hx, Hy, Hz) and two components of electric field (Ex, Ey) in time series data
(Measurement time: More than 14 hours per one station)
TEM method: One component of magnetic field (Hz) of transient response
・Number of Frequency for Data Processing and Analysis
MT method: 80 frequencies ranging from 320 Hz to 0.00034 Hz
TEM method: Two kinds of repeat rate: 2.5 Hz and 25 Hz
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3.2.2 Results of Survey
(1) TEM Survey
TEM survey was conducted at all stations of the MT measurement. Regarding the acquired data quality,
although data scatters were observed in a few windows at later times in several stations, good quality
data applicable to 1D inversion analysis were acquired. 1D inversion analysis of resistivity layer was
executed using the observed data at each station. Layered resistivity structures, which show the
resistivity variation of high-low-high from surface to deep zone were obtained at almost all stations.
From these results, MT responses were calculated and the apparent resistivity and phase curves were
created; and the offset values for static correction were estimated. After applying the offset values to the
apparent resistivity curves observed through the MT method, 2D inversion analysis of resistivity
structure was executed. The list of offset values for static correction and the results of 1D inversion
analysis of resistivity layer are at the back of the report.
(2) MT Survey
After the acquired data were processed using the local reference method or the remote reference
technique, the apparent resistivity and phase curves were created, and the data quality of each measuring
station was evaluated. The data qualities of almost all stations from high frequencies to low frequencies
were good. Although at some stations, the apparent resistivity curve shows a little scatter in local
reference data processing, noises were reduced and data quality was improved after remote reference
data processing and data editing.
3.2.3 Results of 2D Inversion
The location map and stations map of MT and TEM surveys are shown in Figures 3-1 and 3-2,
respectively. The list of the coordinate system of the stations is at the back of the report.
As described above, the good data has been acquired from the high frequencies to low frequencies, and
the resistivity structure between -10,000 m elevation and the surface was estimated. But in the following,
the characteristics between -5,000 m and the surface were described. This range is important to
construct the geothermal reservoir model. And in order to explain the trend of resistivity distribution,
resistivity value of 100 ohm-m was used as a criterion.
(1) Resistivity Cross Section Map
The following are the characteristics of the resistivity structure from each cross section of the profile.
HNL100 profile (Figure 3-3)
The shallow zone is conductive, and the deep zone is resistive from the ground surface to the deep zone
of -5,000 m elevation. From 4 ohm-m to more than 2,500 ohm-m resistivity is distributed on the whole
cross section. The low resistivity of less than 100 ohm-m is distributed from the surface to about -1,500
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m elevation in the southwest part and from the surface to about -800 m elevation in the northeast part.
This low resistivity layer of less than 100 ohm-m tends to become thin gradually from southwest to
northeast. At around -5,000 m elevation, the highest resistivity is shown in the northeast side and from
northeast to southwest, the resistivity value is decreasing. From -5,000 m elevation to the downward
direction, the resistivity value is becoming lower.
HNL200 profile (Figure 3-4)
Same as the case of HNL100 profile, the shallow zone is conductive, and the deep zone is resistive. The
range of resistivity is from 2 ohm-m to more than 2,500 ohm-m. The low resistivity of less than 100
ohm-m is distributed from the surface to about -1,800 m elevation in the southwest part and from the
surface to about -900 m elevation in the northeast part. This low resistivity layer of less than 100 ohm-m
tends to become thin gradually from southwest to northeast. At around -5,000 m elevation, the highest
resistivity is observed in the northeast side and from northeast to southwest, the resistivity value is
decreasing same as in the HNL100 profile.
HNL300 profile (Figure 3-5)
Same as HNL100 and HNL200 profiles, the shallow zone is conductive, and the deep zone is resistive.
The range of resistivity is from 1 ohm-m to more than 2,500 ohm-m. The lowest resistivity is around the
surface at HNL-306 station. The low resistivity of less than 100 ohm-m is distributed from the surface to
about -1,700 m elevation in the southwest part and from the surface to about -900 m elevation in the
northeast part. This low resistivity layer of less than 100 ohm-m tends to become thin gradually from
southwest to northeast. At around -5,000 m elevation, the highest resistivity is observed in the northeast
side and from northeast to southwest, the resistivity value is decreasing same as in the HNL100 and
HNL200 profiles.
HNL400 profile (Figure 3-6)
Same as HNL100, HNL200, and HNL300 profiles, the shallow zone is conductive, and the deep zone is
resistive. The range of resistivity is from 2 ohm-m to more than 2,500 ohm-m. Around the surface at
HNL-403~HNL-404 and HNL406 stations, the lowest resistivity is observed. The low resistivity of less
than 100 ohm-m is distributed from the surface to about -1,500 m elevation in the southwest part and
from the surface to about -1,000 m elevation in the northeast part. Although this low resistivity layer of
less than 100 ohm-m tends to become thin gradually from southwest to northeast, the contour line of
100 ohm-m shows a little sign of increasing and decreasing. At around -4,500 m elevation, the highest
resistivity is observed in the northeast side and from northeast to southwest, the resistivity value is
decreasing similar with HNL100, HNL200, and HNL300 profiles.
HNL500 profile (Figure 3-7)
The shallow zone is conductive, and the deep zone is resistive, same as with the HNL100, HNL200,
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HNL300 and HNL400 profiles. The range of resistivity is from 3 ohm-m to more than 2,500 ohm-m.
The lowest resistivity is distributed around the surface at HNL-506 station. The low resistivity of less
than 100 ohm-m is distributed from the surface to about -1,400 m elevation in the southwest part and
from the surface to about -800 m elevation in the northeast part. This low resistivity layer of less than
100 ohm-m tends to become thin gradually from southwest to northeast. At around -4,500 m elevation,
the highest resistivity is seen in the northeast side and from northeast to southwest, the resistivity value
is decreasing similar with HNL100, HNL200, HNL300 and HNL400 profiles. The distribution of more
than 2,500 ohm-m resistivity is small in extent compared with the other profiles.
(2) Resistivity Plan Map
The following are the characteristics of the resistivity structure from the resistivity plan map at each
elevation.
100 m elevation (Figure 3-8)
Less than 16 ohm-m resistivity is distributed in the whole survey area. In a large sense, the resistivity
value is going down from west to east of the survey site. At the edge of the northeast part, the lowest
resistivity of 4 ohm-m is observed.
-500 m elevation (Figure 3-9)
The range of resistivity distribution is from 10 ohm-m to 100 ohm-m. From the west side to east side of
the survey site, the resistivity value gradually becomes higher and is highest at the northeast side of the
HNL100 profile. The contour lines extend in the northwest to southeast direction and the contour
interval is almost equal. It means resistivity varies gradually.
-1,000 m elevation (Figure 3-10)
The range of resistivity distribution is from 25 ohm-m to 600 ohm-m. The resistivity value is becoming
higher from the west part to the east part. The contour lines mainly extend in the northwest to southeast
direction same as in the plan map of -500 m elevation. From the center to northeast side of the HNL300
and HNL400 profiles, the contour interval is narrow and this indicates resistivity discontinuity structure.
-2,000 m elevation (Figure 3-11)
The range of resistivity distribution is from 160 ohm-m to more than 2,500 ohm-m. The lowest
resistivity value is seen at the southwest side of HNL300 profile and from west to east, the resistivity
value increases. The contour lines mainly show the northwest to southeast direction same as the plan
map of -1,000 m elevation. From the center to the northeast side of HNL300 and HNL400 profiles, the
contour interval is narrow and it indicates resistivity discontinuity structure.
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-4,000 m elevation (Figure 3-12)
More than 400 ohm-m resistivity is distributed in the whole survey area. The lowest resistivity is shown around at the southwest edge of HNL200 and HNL300 profiles and from southwest to northeast, the resistivity value increases. In the northeast part of the survey site especially, more than 2,500 ohm-m resistivity is largely distributed.
-10,000 m elevation (Figure 3-13)
The range of resistivity distribution is from 250 ohm-m to more than 2,500 ohm-m. In comparison with
the plan map of -4,000 m elevation, the value of the resistivity distribution is totally lower. Less than
400 ohm-m resistivity is distributed widely in the southwest part of the survey area and the resistivity
value increases to the northeast. The contour lines mainly show the northwest to southeast direction.
3.2.4 Conclusions of 2D Inversion
The following are the characteristics of the resistivity structure in Hanle Geothermal Field. And the
panel diagrams of resistivity cross section and plan map are shown in Figures 3-14 and 3-15,
respectively:
・The resistivity structure consists of three zones, namely: conductive overburden, resistive intermediate thick zone, and conductive deeper zone at a depth from the surface to -10,000 m elevation. The resistivity distribution is roughly ranging from 1 ohm-m to 2,500 ohm-m.
・The contour line, as the boundary of 100 ohm-m resistivity between conductive overburden and resistive intermediate zones, is located from -1,500 m to -2,000 m elevation at the southwest side of the survey site, and its location becomes shallow to the northeast direction and is roughly ranging from -500 m to -1,000 m elevation at the northeast side of the survey site.
・In a large sense, resistivity distribution may change from conductive to resistive from the southwest side to the northeast side. From -1,000 m to -2,000 m elevation, the interval of contour lines is relatively narrow. It suggests the resistivity discontinuity which shows drastic change of resistivity value.
・The conductive overburden is thin in the graben part of the survey site and thick in the horst part while the intermediate resistive zone shows a large value in the horst part and a small value in the graben part of the survey site. The location of resistivity discontinuity, which shows drastic change of resistivity, mainly coincides with the boundary between the graben and the horst.
・In all the profiles, the highest resistivity (>2,500 ohm-m) is observed from -4,000 m to -5,000 m elevation and this high resistivity is distributed widely with a central focus on HNL200 and HNL300 profiles.
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Source: The Survey Team
Figure 3-1 Location Map of MT Survey Site
Legend
:MT survey site
:Reference station
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Legend HNL-501
:Location of Station
Source: The Survey Team
Figure 3-2 Location Map of MT Stations
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Figure 3-3 Resistivity Cross Section (HNL100)
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Figure 3-4 Resistivity Cross Section (HNL200)
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Figure 3-5 Resistivity Cross Section (HNL300)
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Figure 3-6 Resistivity Cross Section (HNL400)
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Figure 3-7 Resistivity Cross Section (HNL500)
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Figure 3-8 Resistivity Plan Map (-100 m elevation)
Figure 3-9 Resistivity Plan Map (-500 m elevation)
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Figure 3-10 Resistivity Plan Map (-1,000 m elevation)
Figure 3-11 Resistivity Plan Map (-2,000 m elevation)
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Figure 3-12 Resistivity Plan Map (-4,000 m elevation)
Figure 3-13 Resistivity Plan Map (-10,000 m elevation)
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Figure 3-14 Panel Diagram of Resistivity Cross Sections
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Figure 3-15 Panel Diagram of Resistivity Plan Maps
100m Elev.
-500m Elev.
-1000m Elev.
-2000m Elev.
-4000m Elev.
-10000m Elev.
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Chapter 4 Supplementary Surveys
4.1 Overview of Geology and Topography
4.1.1 Geological Structure
The geological map of the survey area (ORSTOM, 1987) is shown in Figure 4-1. Quaternary volcanic
rocks (Afar Stratoid) are widely distributed in the survey area. Major geological layers are the lower
basalt layer (2.0-2.7 Ma), upper basalt layer (1.8-2.2 Ma), and uppermost basalt layer (1.25 is a -1.65
Ma). Rhyolite layer (1.9-2.6 Ma), which is almost the same age as the lower basalt layer, is developed in
the north. Basalts form a plateau, covering a wide range including the MT/TEM survey area. In addition,
the uppermost basalt layer develops as volcanic corns in the NW-SE direction on the plateau.
From ORSTOM (1987), there are some fumaroles on the plateau of the study area. They appear at the
boundary portion of the lower and upper basalt layers. However, there are no fumaroles on the area
covered by the upper basalt layer.
Source: ORSTOM (1985)
Figure 4-1 Geological Map of the Survey Area
4.1.2 Fault Distribution
For obtaining the fault structure constituting the geothermal system in the study area, the Survey Team
analyzed the fault distribution using terrain data. The ASTER GDEM 30 m grid data has been used in
the analysis to create the inclination distribution and direction maps (Figure 4-2). The parts that are
Survey Area
LEGEND
Alluvium
Basalt (uppermost AfarStratoid: βSIII,1.25-1.65Ma)
Basalt (upper Afar Stratoid:βSII,1.8-2.2Ma)
Basalt (lower Afar Stratoid:βSI,2.0-2.7Ma) and lower
Rhyorlte
N
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considered faults were extracted from the inclination distribution map, and the slope of each fault was
estimated using the inclination direction map.
The estimated fault distribution is shown in Figure 4-3. Fault strike is dominant in the NW-SE direction.
In particular, large-scale fault is recognized in the northeast and southwest end of the lava plateau,
which is inclined to the plain side. Lava plateau forms a horst structure. The main features are described
below.
The fault that developed in the rhyolite layer is not continuous to the upper basalt areas of the lava plateau.
On the geological map, the fault was drawn in the boundary part of upper and lower basalt layers (Figure 4-1). But in Figure 4-2, it is not observed. It is considered that the lower basalt is covered by the upper basalt.
Formation history of the terrain in this region is estimated: (i) the formation of the fault located on the southwest edge of rhyolite, (ii) effusion of the lower and upper basalt, and (iii) formation of large-scale fault that separates the northeast edge of the lava plateau.
Source: The Survey Team
Figure 4-2 Inclination Distribution Map and Inclination Direction Map
Inclination Distribution
Inclination Direction
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Source: The Survey Team
Figure 4-3 Fault Distribution Map
Based on the geological structure and lineament estimation results, geological conceptual cross sectional
map including the study area were created (see Figure 4-4).
Source: The Survey Team
Figure 4-4 Conceptual Geological Cross Section
NESW
Hanle PlainGaggade PlainFumarole
(Not in Scale)
MT Survey Area
Legend
IV. Alluvium
III. Basalt (uppermost Afar Stratoid:βSIII,1.25-1.65Ma)
II. Basalt (upper Afar Stratoid:βSII,1.8-2.2Ma)
I. Basalt (lower Afar Stratoid:βSI,2.0-2.7Ma) and lower
IV
IV
I
II
I
II
III
IIII
III
Plateau
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4.2 Site Survey and Laboratory Analysis
4.2.1 Surface Manifestation
In order to confirm the distribution of geothermal manifestations in the survey area, geological
reconnaissance was conducted in parallel with the geophysical surveys. As a result, the fumarole area
has been confirmed in the three sites around the geophysical survey area. Location map is shown in
Figure 4-5.
The maximum temperature and the extent of geothermal manifestations are summarized in Table 4-1.
The largest manifestation is point ③; the distribution of the surface high temperature area is about 500
m (Figure 4-6). It should be noted that the fumarole located at the southern end of point ③ has been
subject to gas analysis in the JICA Survey (2014).
Source: The Survey Team
Figure 4-5 Location Map of Geothermal Manifestation
Table 4-1 List of Geothermal Manifestation Site Number Max. Temp. Length Width Direction
① 96.2 About 140 m Max. 30 m NNW-SSE ② 96.4 About 80 m Max. 30 m NE-SW ③ 99.8 About 500 m Max. 130 m NW-SE
Source: The Survey Team
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Source: The Survey Team
Figure 4-6 Distribution Map of Geothermal Manifestation
500m
Garabbayis-1
50.9
90.8 94.7
90.7
93.8
99.292.6
80m 140m
Site ① Site ②
Site ③
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4.2.2 Geochemical Survey
(1) Objectives
Last year, a gas geochemical survey was conducted for a fumarole located in Garabbayis, Hanle under
the JICA Survey (2014). The survey conducted this year is an additional survey, to study more precisely
the area and chemical change of the geothermal steam supplied. For this purpose, two fumaroles
including the one surveyed last year were examined. Also, the distribution and temperature of spots of
hot and wet soil were investigated. The spots of the hot and wet soil mean that the small area lacks
steam but is wet by the hot water condensed from the fumarolic steam at the surface.
(2) Survey Area
The survey area is shown in Figure 4-7. The area contains an existing test well "Garabbayis-1 (435 m
depth) and geothermal manifestations (fumaroles and spots of hot and wet soil) located east of the well.
Figure 4-8 shows photographs of the geothermal manifestations, and Figure 4-7 depicts the distribution
of temperature of the manifestations. Among these fumaroles, the two strongest fumaroles were
sampled.
Fumarole (FR) No. 1: A fumarole that was examined last year. Fumarole (FR) No. 2: A fumarole about 130 m away from FR No. 1 in the NNW direction.
Figure 4-7 Geochemical Survey Area Source: The Survey Team
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Source: The Survey Team
Figure 4-8 Photographs of Geothermal Manifestations in Garabbayis
(3) Results and Discussion
Table 4-2 shows the results of chemical analysis for fumarolic gas sampled in the last two years (FR No.
1 in 2014 and 2015, and FR No. 2 in 2015). The He-Ar-N2 trilinear diagram, which is based on the
analytical results, is shown in Figure 4-9. In this figure, other fumarolic gas samples taken in other
geothermal fields in Djibouti are plotted.
As seen in Figure 4-9, FR No. 2 and FR No. 1 (2014) show the same chemical composition even though
the two samples were taken from different fumaroles in different years. Because the composition shows
less contribution of atmospheric component, the fumaroles are obviously supplied with geothermal
steam originating from a geothermal reservoir. In addition, other fumaroles and spots of hot and wet soil
are distributed around the two fumaroles sampled. These geothermal manifestations are distributed in
the NW-SE direction with length of about 500 m and maximum width of 130 m (Figure 4.1). As a result,
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it can be said that the geothermal steam found in the FR No. 2 and FR No. 1 (2014) are supplied in the
500 m long area of the manifestations.
Although FR No. 1 (2015) was sampled at the same position of FR No. 1 (2014), the sample showed
almost same composition as the atmospheric one in Figure 4-9. This indicates that the mixing ratio of
atmospheric component in the gas sampled in 2015 is larger than that in 2014. This might be because
the supply of geothermal steam could have been somewhat less during the survey in 2015.
Table 4-2 Results of the Chemical Analysis for Fumarolic Gas in Garabbayis
Source: The Survey Team
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Gas geothermometers were applied to the gas composition of FR No. 2, and the results were
compared with that of FR No. 1 (2014). The geothermometers used are H2/Ar, CO2/Ar, and CH4/CO2.
Calculated temperatures are described as tHA, tCA, and tMC, respectively. These gas geothermometers are
influenced by changes in temperature and redox state while the steam ascends. The response to those
changes can be more rapid in the order of H2/Ar, CO2/Ar, and CH4/CO2 geothermometers. Consequently,
it is expected that the tMC geothermometer indicates a temperature of the deepest portion of the reservoir
(generally the highest temperature), and tHA geothermomter offers a temperature of the shallowest
temperature (generally the lowest temperature).
Figure 4-9 He-Ar-N2 Ternary Diagram for Garabbayis Fumarolic Gases
As can be seen in the calculated temperatures in Table 4.1, the temperatures are higher in the order of
tMC, tCA, and tHA, which indicates the expected characteristics of the thermometers mentioned above.
Calculated tHA, which is about 70 °C, is much lower than the temperature measured at fumaroles. For
this reason, tHA is excluded from the estimation of reservoir temperature. Calculated tCA shows a range
from 120 °C to 160 °C, and tMC ranges from 230 °C to 260 °C. From these results, it can be assumed
that there is a geothermal reservoir with the highest temperature of 260 °C at the depth of Garabbayis.
(4) Conclusion
In the east side of an existing test well, Garabbayis-1, fumaroles and spots of hot and wet soil are
distributed in the NW–SE direction with a length of 500 m. Geothermal steam producing the geothermal
manifestations can be steadily supplied from a geothermal reservoir which has the highest temperature
of 260 °C. Based on this interpretation, it follows that Garabbayis is an appropriate location for new test
drilling to prove the presence of a geothermal reservoir.
Source: The Survey Team
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Chapter 5 Geothermal Reservoir Model and Target for Geothermal Test Wells
5.1 Construction of Conceptual Model
5.1.1 Geothermal Reservoir and Resistivity Structure
Examples of typical underground resistivity structure observed in geothermal area, refer to the findings
of Iceland (Arnason et al (1987): Figure 5-1).
As a feature of this resistivity structure, the following three points are stated: 1) the resistivity
structure is divided into three zones such as the upper high resistivity zone, lower resistivity zone,
and high resistivity zone, 2) discontinuous structure (vertical fault) appears in horizontal direction,
and 3) the range of resistivity shows from several ohm-m to several hundred ohm-m.
Figure 5-1 Geothermal Reservoir and Resistivity Structure
This resistivity structure is correlated with hydrothermal alteration zoning and corresponding
temperatures as shown in Table 5.1.
Table 5-1 Relation between Resistivity and Alteration Minerals and Temperature Resistivity Relation with Alteration Mineral (Zone) Estimated
TemperatureUpper zone
Several hundreds – several thousands Ωm
<Non alteration zone.> Volcanic ash, surface deposit, non-alteration volcanic rocks 50-100 oC
Low resistivity zone
Below 10 Ωm (or 5 Ωm)
<Clay zone (Cap rock)> Alteration zone including smectite, Mixed layer clay mineral, zeolite
100-250 oC
High resistivity zone
Several tens to several hundreds Ωm
<Chlorite – epidote zone (Reservoir)> Alteration zone including chlorite, illite, epidote (and garnet) 250-300 oC
Source:METI (2010) supplemented by The Survey Team
Árnason et al. (1987)
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The resistivity structure of Hanle shows larger resistivity, which does not necessarily correspond to
the typical pattern. Table 5-1 may not be adopted in the case of the Hanle site. This may be because
that alteration in Hanle has not been developed well yet.
However, from the fact that there is a clear geothermal manifestations in Hanle site, the presence of
a geothermal reservoir of different resistivity structure is estimated.
The resistivity structure revealed by the survey in Hanle is interpreted as follows: the topmost
several tens Ωm may correspond to alteration zone (cap rock structure); the lowest zone of 1,000
Ωm or more may be an intrusion, which may be interpreted as a heat source; and the zone in
between the two may be the reservoir. For this reason, distribution area of reservoir was estimated
by shown in following chapter.
5.1.2 Resistivity Structure of Hanle Site
The correlation between resistivity and geothermal reservoir structure was examined in reference to
the past test wells drilled in Hanle in the 1980s. The drilling record of one previous well, Hanle-2
(2,038 m), indicates smectite and chlorite, which are good indications of cap rock and reservoir,
respectively. The depths and resistivity were correlated.
The lowest depth of cap rock is correlated with 40 Ωm, which corresponds to the lowest depth of
smectite emerging; whereas the depth of reservoir is correlated with 160 Ωm, which corresponds to
the bottom depth of the Hanle-1 well, at the bottom of which chlorite emerges.
Table 5-2 Geothermal Structure and Resistivity Zone Resistivity Geothermal Structure Elevation
Upper low resistivity zone 40 Ωm or less Cap rock -500 m or shallower
High resistivity zone From 40 to 160 Ωm Geothermal reservoir -500 m to -2000 m
Ultra high resistivity zone 1,000 Ωm or more Heat source -2000 m or deeper Source: The Survey Team
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Source: The Survey Team
Figure 5-2 Resistivity and Alteration Mineral
5.1.3 Preliminary Geothermal Reservoir Model
The observations/information and interpretations necessary for the construction of preliminary
geothermal reservoir model are summarized in Table 5-3, based on the past survey results and the
geophysical survey conducted.
Table 5-3 Summary of Observations and Interpretations Observation Geothermal System Interpretation
Temperature at 500 m depth of the past 5 test wells increases from the plain side to the plateau side (40 ºC 90 ºC 120 ºC) Heat source
The heat source may exist under the plateau area.
Fumaroles are observed only in the plateau area.
The confirmed fumaroles seem to be on the extension line of the major faults.
Reservoir Fumaroles may emerge along the faults in rhyolite and/or lower basalt layer.
The confirmed fumaroles exist on the margin of the upper basalt.
Reservoir The upper basalt may act as the cap rock of the reservoir.
The fumarole includes mantle origin gas, and the geothermometer indicates 260 ºC
Fluid Fluid with high temperature may exist.
Groundwater level in the Hanle Plain is higher than that in the plateau area.
Fluid recharge There may be recharging from the plain side to the plateau side.
There is a distinct difference of resistivity structure between the plain side and the plateau side.
Regional geological structure
There may be major fault between the plain and the plateau.
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Ultra high resistivity zone (1,000 Ωm or more) is identified below elevation -3,000 m in the plateau side.
Heat source This may be an intrusion body that retains high temperature.
Source: The Survey Team
Based on the above information and interpretation, the following three cases are proposed as the
preliminary geothermal reservoir model.
Table 5-4 Preliminary Reservoir Conceptual Models Case (a)
Figure 5-2 Case (b)
Figure 5-3 Case (c)
Figure 5-3 State of reservoir Not passed much time from
the heat source intrusion High temperature reservoir is present locally
Geothermal system is fully developed Geothermal fluid circulates, and reservoir is formed over a wide range
Heat supply from the heat source is attenuated, and reservoir temperature decreases
Res
ervo
ir
Area/zone Under the plateau Along faults Along major faults only where fumaroles are confirmed
Permeability (hosted rock)
High Low Low
Temperature 260 260 260
Flu
id Origin Originated from the Hanle
Plain Originated from the Hanle
Plains Originated from the Hanle
Plain
Upflow Along fractured faults Along fractured faults Along the major fault only Heat source An intrusive rock below 3 km
Source: The Survey Team
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Source: The Survey Team
Figure 5-3 Geothermal Conceptual Model: Case (a)
Elevation: -1,000 m
SW NE
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Source: The Survey Team
Figure 5-4 Geothermal Conceptual Model: Case (b)
Elevation: -1,000 m
SW NE
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Source: The Survey Team
Figure 5-5 Geothermal Conceptual Model: Case (c)
Elevation: -1,000 m
SW NE
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5.1.4 Preliminary Evaluation of Geothermal Potential
The reservoir resource assessment was conducted with volumetric method together with Monte
Carlo simulation, based on the conceptual case (a).
(1) Volumetric Method
The prevailing calculation methods include parameters that may not have been clearly defined and
therefore users are having difficulty in finding the appropriate specific digits for them. The
following equation was proposed by the paper (S. Takahashi and S. Yoshida, 2015) assuming a
single flash cycle, thereby parameters except the underground related parameters may be clearly
defined.
)()(ζ FLTTCVRE refrgex [kJ/s] or [kW] (1)
ffrr CCC )1( [kJ/s] or [kW] (2)
Where ηex: energy coefficient of turbo-generator, ζ:Effective energy allocation function, φ:
porosity of the reservoir rock, ρr:Density of the reservoir rock, Cr: Specific heat of the reservoir
rock, ρf:Density of geothermal fluid in the porosity of the reservoir rock, and Cf: Specific heat
of the geothermal fluid in the porosity of the rock.
Temperatures of the separator and the condenser are assumed as 151.8 ºC (5 bar) and 50 ºC,
respectively, taking into account the heated conditions of Djibouti. In addition, since the term
RgρCV(Tr-Tref) in the equation (1) represents the heat collected at the well head and cast into the
separator through heat insulated pipe system without losing heat energy, Tref=0.01 . The effective
energy allocation function is given below.
132538 1059.41019.41013.11014.1ζ rrr TTT (3)
The energy efficiency is given by an approximate equation obtained from the data of existing power
plants. When the separator temperature and condenser temperature are 151.8 ºC and 50 ºC,
respectively, the efficiency is:
ηex= 0.77 ± 0.05 (4)
Recovery factor is:
Rg= 0.05 ~0.20 (5)
(2) Probabilistic Method - Monte Carlo Simulation
Crystal Ball of Oracle Inc. was used for the Monte Carlo Simulation. The variable parameters are (1)
reservoir temperature and (2) porosity and reservoir volume with triangular distribution.
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(3) Assumed Parameters
Parameters used for the calculation are shown in Table 5-5. The major parameters are as follows:
Reservoir Volume: The minimum reservoir volume was set as zero since there will be a possibility that the reservoir may not be identified.
Average Reservoir Temperature: The average reservoir temperatures are set from 200 ºC to 260 ºC with the median of 230 ºC, based on the geothermometer analysis results.
Table 5-5 Parameters for the Volumetric Method
Source: The Survey Team
(4) Preliminary Resource Assessment
The assessment results are shown in Table 5-6.
Table 5-6 Preliminary Resource Assessment Capacity (MW)
80% Most Probable 20%
16.9 32.8 86.4
Source: The Survey Team
The estimated preliminary resource is classified into the Inferred Geothermal Resource that shall be examined by a test well drilling supported by supplemental subsurface survey.
Min. M.L Max.
Volume V m3 0 9.50E+09 1.50E+10 Triangle
Reservoir temperature Tr ºC 200 230 260 Triangle
Rock density ρr kg/m3 - 2600 - fixed
Rock volumetric specific heat Cr kJ/kg - 1 - fixed
Fluid volumetric density ρf kg/m3 - 950 - fixed
Fluid specific heat Cf kJ/kg - 5 - fixed
Porosity Φ % 5 - 10 Uniform
Recovery factor Rg % 5 20 Uniform
Reference temperature forflash type
Tref ºC - 0.01 - fixed
Rejection temperature(condenser temperature) *
T0 ºC - 50 - fixed
Separator temperature* - ºC - 151.8 - fixed
Exergy efficiency for flash ηex % 72 77 82 Triangle
Plant factor F % - 90 - fixed
Plant life L year - 30 - fixed
Parameter Symbol UnitRange Probabilistic
distribution
Min.: Minimum; Max.: Maximum, M.L.: Most likely; tbp: to be proposed; *: given in the heat allocationf i
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5.2 Target for Geothermal Test Wells
A test well target is examined using a probable geothermal system model. Test well drilling is
expected to meet fractures with high temperature and permeability, and the fractures can be
associated with faults. For this reason, targets for a new test well in Garabbayis are examined using
the three geothermal models that include inferred faults as mentioned in Section 5.1.
Each of the models shows the distribution of geothermal reservoir along with the faults. Among
them, Fault #1 is recognized as a main reservoir in any of the models. Furthermore, the fault is
beside active surface manifestations, which means that Fault #1 is the highest priority as a target for
the new test drilling in Garabbayis, Hanle. Design of drilling targets comprises three factors, i.e.:
target position on the map, target depth, and wellhead location. For this design, the Garabbayis map
shown in Figure 5-6 was used. The map contains Fault #1, geothermal manifestations, and the well
pad for the existing Garabbayis-1 test well.
(1) Target Position on the Map
As seen in Figure 5-6, a part of Fault #1 overlapping the geothermal manifestations can be the target
zone. In that zone, the locations of the most active manifestations can be a candidate for the target
position on the map, as shown by a red circle in Figure 5-6.
Figure 5-6 Map for Planning of a New Test Well Drilling in Garabbayis
Source: The Survey Team
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(2) Target Depth
Target depth should correspond to the depth of a high temperature in the models. The altitude of the
isotherm of 250 °C is set at around -1,200 mASL in the models; thus, the target depth should be at
least 1,500 m from the surface whose altitude is ca. 300 mASL. Considering more the uncertainty of
the isotherm in the models, the target depth should be set at the depth ranging from 1,500 m to 1,800
m (-1,500 mASL) as shown in Figure 5-7.
Figure 5-7 Target Depth in the Geothermal Reservoir Model
(3) Wellhead Location
The well pad of the Garabbayis-1 well can be used for a new test well. The well pad is made of
concrete, offering a rigid and flat base for the drilling rig.
(4) Preliminary Drilling Plan
On the basis of the location of targets, preliminary drilling plan was examined. The plan has to deal
with total drilling depth (TD), total vertical depth (TVD), and deviation of the well track. In the case
where the well pad for Garabbayis-1 is used also for the new test well, the deviation should be 300
m to reach the farthest target. This deviation and targeted TVD (1,800 m) require a TD of 2,000 m
with an inclination of the well less than 30 °. This plan is sufficiently acceptable with a normal 2,000
m class drilling rig.
Source: The Survey Team
Fault -1
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Chapter 6 Preliminary Economic Analysis for IPP Participation
The government of Djibouti intends to introduce IPP for construction, operation and maintenance of
geothermal power station, once geothermal resources are confirmed. This chapter describes an
analysis of economic viability for a case where an IPP should participate in the project as the power
generation operator.
The preliminary reservoir assessment conducted with probabilistic approach resulted in 32 MWe,
86.4 MWe and 16.9 MWe for the most probable occurrence, 20 % probable occurrence and 80 %
probable occurrence respectively. Out of these, the assessment results of the probable occurrence of
80% shall be taken as the installed capacity when we examine an economic viability for the IPP
participation. We thus assume the capacity of the Hanle geothermal power station at 15 MWe.
The examination of economic viability was conducted through a comparison between the IPP
breakeven power sales price sold out at the Hanle power station and the power purchase price by
EDD at the substation of Ali Shabieh, with an assumption that the Hanle geothermal power station is
connected with the existing substation at Ali Shabieh via overhead power transmission line.
6.1 Assumptions
For the examination, assumptions are presented in Table 6-1 as follows.
A plant factor 80% is assumed that is recommended to use for planning purposes by the Ministry of Economy, Trade and Industry of Japan, while a 90 % is assumed in ESMAP (2010).
IPP shall bear the construction cost, except for the cost for test well drilling.
Two cases of 60% and 70% as the well successful rate, since success of failure of well will have a significant impact on project economics.
Costs for test wells are not included in the examination. Grant assistance from other sources is expected. Test wells are not to be converted to production wells even if successful.
Table 6-1 Assumptions for Examination of IPP Breakeven Power Price Items Assumptions Notes
Plant capacity 15 MW P = 80 % Plant factor 80 % Standard of Japan Cost bearing body IPP except for cost of test wells Well success rate 60 %, 70 % (for 2 cases) Cost of test wells Grant (8.4 M USD) 3 slim holes Use of test wells Not used for production wells
Source: JICA Survey Team
6.2 IPP Breakeven Power Sales Prices at the Power Station
The IPP breakeven power sales prices sold out at the Hanle geothermal power station are shown in
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Table 6-2 below. Construction costs were determined with reference to past records around the
world, taking into account scale effects of capacity. The calculation sheets used are included in the
attachments.
As the results, the IPP breakeven power sales prices were calculated as 0.616 USD/kWh and 0.145
USD/kWh for each well successful rate of 60 % and 70 % respectively.
Table 6-2 IPP Breakeven Power Sales Prices Sold-out at the Hanle Geothermal Power Station Well Successful Rate 60 % 70 %
Construction cost 104.5 M-USD (7.0 M-USD/MW) 98.4 M-USD (6.6 M-USD/MW)Breakeven price at power station 0.161 USD/kWh 0.151 USD/kWh
Source: JICA Survey Team
6.3 Transmission Cost
The Hanle geothermal power station will be connected to the nearest substation of 63/20 kV at Ali
Sabieh approximately 70 km from the Hanle geothermal power station; the Ali Sabieh substation
being connected to the main substation at PK12 via 63kV transmission line. The following
assumptions in Table 6-3 are made in order to calculate the transmission cost from the Hanle
geothermal power station (15 MWe) to the substation at Ali Sabieh.
Table 6-3 Assumptions for Transmission Cost Calculation Items Assumptions
From and to From Hanle to Ali Sabieh Distance 70 km Capacity 63 kV Construction cost 17.5 M-USD (0.25 M-USD/km) Cost bearing body EDD
Source: JICA Survey Team
The transmission line will be of 63 kV, and approximately 70 km long; construction cost is
estimated at 0.25 m-USD/km; EDD will be the responsible body for the construction and, operation
& maintenance. Calculation sheets used are included in the attachment. As the result, the
transmission cost was calculated at 0.021 USD/kWh/
6.4 Power Purchasing Cost at Ali Sabieh Substation.
From the calculation results explained above, the power purchasing cost at Ali Sabieh substation by
EDD are shown in Table 6-4.
If the power plant is constructed with a successful rate 60% of production wells, the power purchase
cost at Ali Sabieh substation by EDD will be 0.182 USD/kWH; whereas the cost will be 0.172
USD/kWh if the successful rate should be 70 %.
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Table 6-4 Power Purchasing Cost at the Ali Sabieh Substation Well successful rate 60 % 70 % Note
IPP breakeven cost (USD/kWh) 0.161 0.151 IPP minimum sailing price of electricity at power stationTransmission cost (USD/kWh) 0.021 0.021 63 kV, 70 km EDD bearing cost (USD/kWh) 0.182 0.172 Minimum cost of electricity at Ali Sabieh substation
from Hanle geothermal Source: JICA Survey Team
6.5 A comparison with the power generation cost at the existing power plants
Euei odf (2013)1 reports that the fuel cost accounting to a significant part of the power generation
cost was 180.4 USD/ MWh (0.180 USD/kWh) in 2013. A comparison of the Hanle geothermal
power plant (15 MWe) with the existing power plants thus results in:
When the well successful rate is 60%, both case will have similar economic implication,
When the well successful rate is 70%, the Hanle geothermal power station will economically superior to the existing power plants.
If the transmission should be constructed with a financial arrangement that should exempt EDD
from bearing or repaying, the Hanle geothermal power station will superior to the existing thermal
plants in both cases of the well successful rate 60% and 70 % will.
6.6 Conclusions
With information available at this stage, the reservoir resource of the Hanle geothermal prospect was
evaluated at 15 MWe as the probable occurrence 80% that should be considered when IPP project is
to be planned. This capacity is as a similar size as of a small hydropower plant. However, the Hanle
geothermal power station will be economically superior to the existing oil thermal power plants if
the transmission line should be constructed without financial burden to EDD.
Presently, a significant part of the electricity is being purchased from Ethiopia. Although Ethiopia
still has a large capacity of hydropower energy, the power purchase agreement between the two
countries have entered into only for a period of Ethiopia wet seasons. On the other hand, power
plants within Djiboutian territory are all of oil thermal power plant. Therefore, Djibouti does not
actually have any power plants of indigenous energy source.
Under this circumstance, constructing the Hanle geothermal power station, though the capacity is 15
MWe together with transmission line will be justifiable not only from economical point of view but
also energy security point of view too.
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Chapter 7 Procedure of Environmental and Social Considerations
7.1 Environmental and Social Impact Assessment Study
Decree 2011-029/PR/MHUEAT (2011) shall be referred to for the Environmental Social Impact
Assessment (ESIA), which describes the procedures to be followed. The decree classifies the
assessment into two categories: (1) basic and (2) detailed. The detailed assessment is required for
test well drilling and plan construction. Figure 7-1 shows the flow of procedural instruction.
Source: JICA Survey (2014)
Figure 7-1 ESIA Procedures
Project Proponent
National Government
Expert Team
Technical Committee
Citizens
Draft Terms of Reference
Order to check the Terms of Reference
Site survey
Opinion
Final Terms of Reference
Survey, Forecast, Evaluation
Draft EIS Report
EIS Report
Public hearing Opinion
Order to check theEIS report
Publicity
Opinion
Grant for Environment
Clearance
Opinion
Final EIS
Desk study andDetail study
Evaluation
Monitoring and taking measures to
protect the environment
Periodical report
Environment Audit Report
END
Inspection
Opinion
Implementation of EIA
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Assessment of the terms of reference (TOR) by the competent office needs about one month at least,
Survey and report preparation may take two months,
Assessment and approval of the report needs about three months, and
A total of about six months are required to start the test well drillings.
7.2 Review of Existing Surveys(ESIA for Asal Geothermal Project)
The Government of Djibouti is now in the process of conducting test well drilling in the Asal
Geothermal Project with financial arrangement from the World Bank and others. ESIA was
conducted by Fichiner in 2012 and the report is on the website of the Word Bank.
The ESIA report conducted a field survey for the social conditions, and referred to the past well
drilling record for the natural environmental assessment together with interview survey.
7.3 Draft Terms of Reference
Since an ESIA is required before test well drilling in Hanle, a TOR has been drafted based on the
results of the ESIA report for Asal in order to realize smooth implementation of the test well drilling.
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Chapter 8 Proposal for Additional Surface Survey In the previous sections of this report, three types of geothermal reservoir models were proposed
based on the MT/TEM survey conducted together with the information from past investigations. The
resistivity structure obtained in Hanle has been revealed to be different from that of a typical
geothermal reservoir. Although the next step for geothermal development is test well drilling, the
Survey Team considers it prudent and necessary to verify the appropriateness of the proposed three
geothermal reservoir models through additional surface survey. By this additional survey, the well
target could also be refined. In addition to the scientific survey, data collection and analysis will also
be necessary to prepare for the drilling works.
This chapter describes the issues to be solved as well as proposes survey to solve these issues in
order to realize test well exploration.
8.1 Issues to be Solved to Realize Test Well Exploration
The following are the issues to be solved before implementation of test well exploration:
・To verify the appropriateness of the interpretation of geological structure (geological characteristics
of the Hanle Plain and the plateau).
A number of faults have been objectively confirmed by the lineament analysis using DEM
data. The MT/TEM survey identified one major fault between the Hanle Plain and the plateau.
Distribution of fracture together with regional geological structure has to be clarified.
・To improve knowledge on the characteristics of reservoirs
The resistivity structure of Hanle is different from that of a typical geothermal reservoir. Even
though, the Survey Team proposed three reservoir models based on the fact that there are
geothermal manifestations. The appropriateness of these models, however, has to be verified
with additional surface survey before test well exploration because the information at hand is
considered not to be enough to confidently propose the reservoir model which could allow
more reliable resource estimation. The drilling target may also be refined with the additional
information.
・To understand the extent of the sheeted high resistivity zone below, and the very low resistivity
zone in the surface zone of the northeast side of the plateau
The high resistivity zone below is considered to be the heat source that would originate from
intrusive rock; and the low resistivity zone in the surface zone of the northeast side of the
plateau may form the cap structure of the reservoir. These resistivity structures extend
beyond the present MT/TEM survey area. Since these are considered to be very important to
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examine the geothermal system, the survey area has to be widened. This is also important to
review the size of the reservoirs.
8.2 Proposal for Additional Survey
The following three surface surveys are proposed: (1) gravity survey, (2) additional MT/TEM survey,
and (3) micro-seismicity monitoring. In addition, the following surveys are proposed which are
necessary for smooth implementation of test well exploration in the shortest time period: (4) ESIA
for test well drilling and (5) preparatory survey for test well drilling works. The explanation for each
survey is as follows:
(1) Gravity Survey
The gravity survey is proposed to identify regional geological structure, detailed geological anomaly
in and around the reservoirs, and distribution of the deep sheeted high resistivity geology.
A set of 300 measuring points are proposed with an interval of 1,000 m for regional investigation
and 500 m in and around the geothermal reservoir. The layout of the measuring points is shown in
Figure 8-1.
Source: The Survey Team
Figure 8-1 Layout of Gravity Survey Measuring Stations
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(2) Additional MT/TEM survey
The additional MT/TEM survey is proposed to grasp the distribution of the deep sheeted high
resistivity zone and the low resistivity zone of the surface area in the northeast of the plateau.
About 36 measuring points are proposed in the area neighboring the northern boundary of the
previous MT/TEM survey points with an interval of approximately 1 km as shown in Figure 8-2.
The additional survey will cover the fumarole points shown in the geological map in the north of the
previous survey area. The survey will provide an underground information on a wider area of the
plateau.
3D inversion method is proposed to analyze the obtained data.
Source: The Survey Team
Figure 8-2 Layout of the Additional MT/TEM Survey Points
(3) Micro Seismicity Monitoring
Micro seismicity monitoring is proposed to investigate the structure, extension, and fluid activity
area of the geothermal reservoirs. This would provide information on the size of reservoirs.
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A set of five monitoring points is proposed that encompasses the expected reservoir area in the
middle as shown in Figure 8-3. Access conditions to the monitoring points are also considered. A
minimum of three months are allocated for the monitoring.
Based on Lépine and Hirn (1992), microseismicity monitoring has been conducted twice on Hanle site.
The first monitoring has been carried out using the 7 seismometers in the period of March 1985 to June
1986 (Figure 8-4). At that time, swarm considered to be due to geothermal activity was observed below
the fumarole area (Figure 4-5, ①) in depth of 3km. The second monitoring was performed using 30
seismometers in late 1986 (about three months). At this time, 10 events has been observed in depth of
8km or deeper.
Source: The Survey Team
Figure 8-3 Layout of Monitoring Station of Micro Seismicity
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Source: Lépine and Hirn (1992)
Figure 8-4 Location of Micro Seismicity
(4) ESIA ESIA for test well drilling is proposed in accordance with the proposed TOR. It will take at least six
months from the submission of TOR to the competent governmental authority for final approval.
This is important if the test well drilling should be implemented at earliest convenience.
Source: The Survey Team
Figure 8-5 ESIA Process for Test Well Drilling
MT/TEM Survey Area
Swarms
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(5) Preparatory Survey for Test Well Drilling Works (Contractual and Procurement Matters)
Djibouti has experiences in conducting test well in the 1980s; but since then, the activities were
suspended. There is actually few information regarding availability of drilling machines, drilling
contractors, and modes of contract together with cost information. For smooth implementation of
the test well drilling works, the following survey is proposed:
Information collection and analysis on payment terms for drilling works
Proposal for the most optimal contract conditions
Availability of drilling contractors
Work planning
Preliminary drilling works plan (drilling program, material procurement, etc.)
Preliminary civil works plan (Access road, water supply, electricity, etc.)
Preliminary cost estimation for test well drilling works
8.3 Preliminary Work Schedule up to Test Well Drilling
A preliminary work schedule up to test well drilling is proposed in Figure 8-6 below.
Source: The Survey Team
Figure 8-6 Preliminary Work Schedule up to Test Well Drilling
SpecificationPreparationMeasurment 300 pointsAnalysis Reporting
PreparationSetting up 5 monotoring postsMeasurment 3 monthsAnalysis Reporting
3 Additional MT/TEM surveyPreparationMeasurment 36 pointsAnalysis Reporting
ScopingTOR apprisalFeid surveyApprisal
6 Preparation survey for test well drilling planingMarket surveyContractual aspectPreliminary PlaningPreliminary cost estimation
4 Integrated analysis5 ESIA
6th 7th1 Gravity Survey
2 Micro scismisity monit
Moths 1st 2nd 3rd 4th 5th
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Chapter 9 Activities of Other Donors
Information on other donors’ activities are described below based on the interview survey with
ODDEG, because the donors concerned are not stationed in Djibouti.
9.1 United States Agency for International Aid (USAID) - A workshop was conducted on independent power producers (IPP) and public private
partnership (PPP) for the energy sector in October 2014.
- An expert was appointed in 2014 to promote IPP or PPP projects in the energy sector. It is understood that an aim of this support is to build a consensus for implementation of Power Africa under the Obama Initiative. The expert had left the country in February 2015.
- An alternative expert has been selected. The expert is not stationed in Djibouti and visits the country intermittently to conduct information collection and exchange. It is explained that the subject appears to be centered on the Asal Project in connection with investment opportunities from the country, and that specific proposals on institutional matters seem not to be made by the expert.
9.2 Support to Asal Geothermal Project by the World Bank (WB) and Other Donors
- The Assal Geothermal Project is being handled by the EDD. The ODDEG and CERD serve like a technical support. Much information therefore is not available.
- Dr. Jalludin, the former director of the Centre for the Study and Research of Djibouti (Centre de Recherche et des Etudes de Djibouti: CERD), and Dr. Kayad of ODDEG are now in charge. The Survey Team did not have the opportunity to conduct an interview with them.
- Information given by ODDEG that needs to be confirmed are as follows:
The project director has been selected as of July 2015.
Procurement of drilling contractor is ongoing. The project seems to be moving.
However, every procedure has to go through the seven donors one by one, which will take a longer process.
Information on the actual implementation of drilling is yet to be made available to the Survey Team
9.3 Support from ICEIDA
The support from the Icelandic International Development Agency (ICEIDA) is categorized in the
following four sections according to the information given by ODDEG:
- Improved project management capacity for geothermal projects and project management system is in place at ODDEG (from May 2015)
- Geothermal drill training (2016)
- Improved capacity for surface exploration - Lac Abhe (from October 2015)
- Technical assistance (finalization of Geothermal Risk Mitigation Facility (GRMF) application and other matters, as applicable)
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ICEIDA supported ODDEG in the preparation of the application to GRMF for the surface survey in
Nord Goubet. Although the expression of interest (EoI) was accepted, the preparation of the full
application was suspended.
9.4 Geothermal Risk Mitigation Facility (GRMF)
The ODDEG submitted the full application to GRMF for the surface survey of Arta geothermal
prospect with the assistance of a Japanese consultant group. The result will be notified by GRMF
by January 2016. If the application is accepted, the surface survey will be conducted by the staff of
ODDEG with the technical advice of the Japanese consultant group.
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Chapter 10 Activities with National Fund
10.1 Procurement of Drilling Machines
The Government of Djibouti is now in the process of procuring a drilling rig from Turkey. The
present conditions are as follows:
- Contract negotiation for purchasing a drilling rig with 2,000 m capacity. The machine would be made available in Djibouti in 2017.
- A second-hand drilling rig with 900 m capacity will be provided from Turkish company, and will be made available in Djibouti in the coming September 2015. The ODDEG intends to conduct training of their staff with this machine.
- Information is yet to be made available to the Survey Team on how these rigs are to be operated when the Asal Project or other projects are to be implemented.
10.2 Construction of the New ODDEG Office at PK 12
It was informed that the construction has almost been completed. The staff are about to move to the
new office.
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Chapter 11 Conclusions and Recommendations
Based on the geophysical MT/TEM surveys together with the review of the past surveys conducted
in the 1980s, and the supplemental geological and geochemical surveys in the Hanle geothermal
site, which the JICA Survey (March 2015) recommended as the first priority for development, the
conclusions and recommendations of this report are as follows:
11.1 Conclusions
【Geothermal Resource Assessment】
1) The Hanle Plain has a main fault in its northwest plateau.
2) The heat source and geothermal reservoir exist underneath the northwest plateau.
3) The resistivity structures obtained by the geophysical survey do not show a similar pattern to the
typical geothermal resistivity structure of a geothermal reservoir. This is the reason why it is
considered that the hydrothermal alteration is not yet well advanced in Hanle.
4) However, the Survey Team considers the geothermal system, which represents that manifestations
in field should consist of the heat source, reservoir, and fluid.
(a) Heat source should be a body that shows high resistivity and is considered to be an
intrusion body.
(b) Reservoir should be fractured faults themselves or together with permeable layers in the
lower basalt, with capping structure made up of upper basalt. The reservoir could be
260 °C according to the geochemical survey that the Survey Team conducted.
(c) Geothermal fluid should be recharged from the Hanle Plain where groundwater level is
higher than in the plateau.
5) A preliminary reservoir assessment with information on the target area based on the survey shows
the following results:
Capacity (MW)
80% Most Probable 20%
16.9 32.8 86.4
However, there will be issues that need to be clarified as described in Section 11.2 below, and
this preliminary estimation shall be reviewed through the clarification of these issues.
【IPP Breakeven Power Sales Prices and Economic Comparison with the Existing Power plants】
The government of Djibouti intends to introduce an IPP for construction and operation of the
Hanle Geothermal Power Station, once the geothermal resources should be confirmed by test
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well drilling that the ODDEG expects financial assistance from donors.
The Survey Team conducted a preliminary economic analysis, assuming that the installed
capacity should be 15MWe, EDD should purchase the electricity at Ali Sabieh substation by
constructing the transmission line from Hanle to Ali Sabieh. The analysis has resulted that the
Hanle geothermal power plant is superior to the existing diesel power plants if the successful
rate of the production wells should be 60% or more.
If the EDD should be exempted from the construction cost of the transmission line from the
Hanle geothermal power station to Ali Sabieh substation, the Hanle geothermal power station
will be much more superior to the existing power plants.
Although the prices of the electricity imported from Ethiopia is much more lower, Djibouti
does not have any indigenous energy sources for electricity; which should be a serious issues
from energy security point of view. It is therefore concluded that the Hanle geothermal
development should be justifiable.
【Environmental and Social Impact Assessment (ESIA)】
An ESIA is required by the Government of Djibouti before implementation of test well drillings
as well as before construction of geothermal plant. The process from the application with TOR
to the approval of ESIA for drilling works will need at least six months. To facilitate the
implementation of the works, the Survey Team has prepared the proposed TOR based on the
one for the geothermal development project in Asal, which is now in the process of project
implementation.
11.2 Issues and Recommendations
【Reservoir Estimation and Decision for Test Well Drilling】
Issues:
The next step after the geophysical survey would be the test well drilling based on a standard
project sequence. However, the resistivity structure of the Hanle Reservoir has been revealed to be
different from the typical resistivity structure. On the other hand, the Survey Team considered the
need to have a geothermal reservoir because clear and strong geothermal manifestations are
observed on site. Although the Survey Team proposed three cases of geothermal reservoir, they do
not have reliable bases for these interpretations and these should be supported with additional 3-G
information. Because the investment costs of test well drilling are considerably large, the Survey
Team considers it prudent and necessary to conduct the additional 3-G survey which will contribute
to the clarity of the geothermal system. With these information, a decision of ‘Go’ or ‘No-go’ for
test well drilling could be made.
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Recommendations:
The following additional surveys have been proposed in this report:
Gravity survey for consideration of geological structure in connection with geothermal reservoir system,
Additional MT/TEM survey for identification of the possible extent of geothermal reservoir,
3D inversion analysis for MT/TEM data, and
Micro-seismicity monitoring for identification of geothermal fluid movement.
【Environmental and Social Impact Assessment ESIA】
Issues
An ESIA process for test well drilling will need at least six months, which may retard the process of
a speedy development.
Recommendations:
It is recommended to conduct such process together with the proposed additional 3-G survey in
order to implement the test well drilling immediately after the additional 3-G survey.
【Survey on Procurement for Drilling Works】
Issues
Djibouti has experiences in conducting test well in the 1980s. but since then, the activities were
suspended. There is actually few information regarding availability of drilling machines, drilling
contractors, and modes of contract together with cost information.
Recommendations:
It is therefore necessary to conduct a survey on procurement matters for the drilling works.
【Preliminary Economic Analysis for an IPP Project】
Issues
The ODDEG intends to invite an IPP for the Hanle geothermal prospect after the confirmation of
geothermal resources. This report conducted a preliminary economic analysis focusing on IPP
project through desk study with available information at hand. The results of this analysis should be
refined with the information on economic factors as well as the results or reassessment of
geothermal resource with additional information to be obtained from the additional 3-G survey.
Recommendations:
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It is recommended to conduct a preliminary economic assessment assuming an IPP project that the
ODDEG intends to introduce.
*** end of report **