PROCEEDING INDONESIAN PETROLEUM ASSOCIATIONTwentieth Annual Convention, October 1991
EVALUATION OF THE DIENG GEOTHERMAL HELD;REVIEW OF DEVELOPMENT STRATEGY
M. Boedihardi*Suranto*
S. Sudarman*
ABSTRACT
The liquid-dominated system of the Dieng GeothermalField in Central Java can be divided at least into threeareas: the northwestern Sileri area, the centralSikidang-Merdada area, and the southeasternPakuwaja area. A total of sixteen exploration anddevelopment wells have been drilled, with one well atSileri, thirteen wells at Sikidang-Merdada, and twowells at Pakuwaja.
Interpretations of existing gravity, magneto-telluric andwell data reveal that the Sikidang-Merdada area isseparated from Sileri and Pakuwaja by zones oflow permeability and low temperature. These lowpermeability barriers show up on the geophysics asregions of gravity highs and conductivity lows. Afumarolic area with an associated gravity anomalyknown as the Siglagah prospect occurs in east of Sileriand represents a target for future exploration.
The total geothermal potential is estimated as 355 MW,of which 175 MW are located in Sikidang-Merdada.A 55 MW project is planned for Sikidang-Merdadato come on line in 1995/96. Modular units arerecommended, consisting of 2x20 MW and 1x15 MWunits. About ten megawatts of capacity currently existat the wellhead and future development wells areexpected to produce 55 tons/hr steam per well.
The reservoir at Sikidang-Merdada consists of a dome-shaped steam zone overlying a brine reservoirwith 2000-3000 ppm chloride and 0.5 to 1.6% non-condensible gas by weight. The reservoir temperatureis as high as 320°C.
1 PERTAMINA-Geothermal Div., EP
INTRODUCTION
The Dieng geothermal field is situated in Central Java,about 26 km north of Wonosobo, the nearest town.Presently, eleven exploration and five production wellshave been completed at Dieng (Figure 1). Thirteenwells have been drilled in the central Sikidang-TelagaMerdada area, one well (DNG-10) at Sileri in thenorthwest, and two wells (DNG-5 and 11) at Pakuwajato the southeast. Existing plans are to develop a 1x55MW unit by 1995 located at the Sikidang-Merdadaarea. About 10 MW of electrical capacity are currentlyavailable at the wellhead for wells in this part of thefield.
Dieng has been the subject of many studies. Themost comprehensive study, which was based on bothexploration and production data, was done by Unocalin 1989. Unocal examined the results of thirteen Diengwells. Since 1989, three additional wells have beendrilled at Dieng, and these provide key data for thereinterpretation of the reservoir characteristics. Theobjective of this study is to utilize the new well data inorder to determine whether the development plan for a1x55 MW unit is still suitable for the Dieng reservoir.
PRODUCTION DATA
Table 1 summarizes the drilling results at Dieng. Of thethirteen wells in the Sikidang-Merdada area, theabandoned wells DNG-1, 4, 7 and 12 had the highestcapacity of 5 to 10 MW, and they produced from about1500-2000 mVD (metre Vertical Depth). Wells DNG-2, 8 and 13 currently produce steam for a total of about10 MW from productive zones between 1500 to 2000m.Three other wells, DNG-3, 6 and 9 are now unusabledue to well damage. The recently completed wells,DNG-14, 15, and 16 are still undergoing testing. WellsDNG-5 and 11 at Pakuwaja have not been tested due to
well damage or low reservoir permeability, althoughthe downhole temperatures are high.
The well production characteristics, such as mass flow,enthalpy, gas content and dryness for the Sikidang-Merdada and Sileri areas are presented in Figures 2 and3. At a WHP (Well Head Pressure) of 15 bars, the totalmass flow in Sikidang-Merdada wells is about 75 tons/hr, enthalpy is about 2200 kJ/kg and gas content anddryness are 5% by weight and 70%, respectively(Figure 2A). DNG-10 in the Sileri area has a slightlylower output of about 65 tons/hr with enthalpy of about1500 kJ/kg and gas content of 4% by weight and 50%dryness (Figure 2B). A high gas content of up to 20%wt, mostly carbon dioxide, was recorded in DNG-2 atthe Sikidang-Merdada area during the initial well tests.During ten years of production to a 2 MW monoblock,the gas content of DNG-2 decreased to 2% wt, and acomputer simulation model indicates further decreasesto about 1% as production continues (Figure 3A, fromGENZL/SDB, 1991). This simulation analysis alsoindicates that the mass flow for a 1x55 MW unit willdecrease from about 125 to 100 kg/s after 30 years ofoperation (Figure 3B).
EXPLORATION AND SUBSURFACE WELLBOREDATA
Surface exploration data, including geology, geophysicsand geochemistry, are discussed in this section andlinked to the wellbore data in order to clearlyunderstand the subsurface conditions of the studiedarea.
A simplified geological map of the Dieng field is shownin Figure 1. This field has 10 lithologic units which arecomposed of andesitic lava, tuffaceous breccia andquartz latite. Potassium-Argon age dating has beendone for some units to give better control to thevolcanic stratigraphy. The Sileri area which isassociated with Gn. Pagerkandang at the north has anage of 460,000 years. Sikidang-Merdada is associatedwith Pangonan of 370,000 years of age. The Pakuwajaarea in the southeast has an age of 90,000 years. Theseage dates show a magmatic migration from northwestto southeast. These three areas have gravity andmagneto-telluric (MT) anomalies (Figures 4A and 4B,respectively). The gravity anomalies are characterizedby low residual gravity at <-4 mgals, while the MTanomalies show a conductance of >1000 Mhos. Thecombined anomalies have sizes of 3 km2 at Sileri,6.5 km2 at Sikidang-Merdada, and 2 km2 at Pakuwaja.The gravity data also shows an anomaly at Siglagah, anarea east of Sileri which has fumaroles. Unfortunately,a few MT coverage is available for Siglagah. Sikidang-Merdada is clearly separated from Pakuwaja by an MT
conductance low and a gravity high. The geophysicaldata show a similar but less pronounced separationbetween Sikidang-Merdada and Sileri.
Major lineaments, which have been interpreted fromaerial photography as faults, are also shown in Figure t.The three main structural trends from the oldest to theyoungest are E-W, NW-SE and NE-SW or N-S. Thesestructural features are likely to control the boundariesof the three prospective areas. Circular features, whichusually represent crater rims, are seen in all areas andtypically have diameters ranging from 0.1 to 1.1 km.
The hydrothermal surface manifestations on the Diengplateau occur on high and low elevation areas. At highelevations such as volcanic peaks and plateau, themanifestations consist of fumaroles, acid sulphateboiling springs, mud pools and intensively alteredground. At lower elevations, the thermal areasare mainly hot and warm springs with temperaturesranging from 35 to 55°C and neutral pH. Thesesprings are numbered on the map in Figure 1, and thecorresponding spring and borehole chemistry appear inthe ternary diagram on Figure 1 and in Table 2. Thewarm and hot springs have bicarbonate-sulphatechemistry, while the wells produce sodium chloridewater. This chemistry suggests that there is no directconnection between the springs and the deep reservoirfluids, thus making chemical geothermometry of littleuse in estimating reservoir temperature. However, thehigh chloride content in the feed zones indicates thatthe reservoir is water dominated.
The dissolved gas in the brine reservoir of the Sikidang-Merdada area has been computed by Suwana (1986)and Fauzi (1987) from well discharge data. Theyconclude that the brine contains 0.5 to 1.6% by weightnon-condensable gas. The chloride concentration in thereservoir brine is between 2000-3000 ppm.
The hydrothermal alteration in the 16 Dieng wells hasbeen studied. Ganda and Suroto (1985) found threemain alteration assemblages with a vertical zonationthat could be correlated with temperature. Argillicalteration is the shallowest, propylitic occurs atintermediate depths, and phyllic at the greatest depth-These assemblages correspond to temperatures of150-250°C, 250-300°C and >300°C, respectively. Theproduction casing shoe is set towards the bottom of theargillic section. Exceptions to the alteration zonationare found at DNG-10 at Sileri, where the phyllicalteration is absent, and in DNG-15, where the hightemperature minerals are undeveloped.
Maps of temperature and pressure of the main feedzones for the entire Dieng field are shown in Figures
349
<A and 5B, respectively. Both data indicate threeanomalous areas:
Sikidang-Merdada (wells DNG-1, 4, 7, and 9) withhigh T and KSileri (DNG-10) with high T and KPakuwaja (DNG-5 and 11) with high T but low K.
The vertical reservoir pressure distribution of theprincipal feed zones for all wells is given in Figure 5B.A linear pressure gradient of 63.2 bars/km is estimatedfrom this figure which is close to the hydrostaticgradient of water at an average reservoir temperatureof 280°C (i.e. 64.6 bars/km). This suggests that liquidwater is the pressure controlling phase. Thus, thereservoir can be classified as liquid dominated which isin accordance with the geochemical data. Wells DNG-1and 12 produce up to 90% steam and have anomalouslyhigh feed zone pressures, suggesting that these wellsintersect vapour zones.
The distribution of reservoir permeability has beendeduced from lost circulation data and by interpretingdownhole temperature changes following injectiontests and flow tests. Figures 6A and 6B show theelevation and the thickness of the main feed zones,respectively. Both the shallowest and thickest resevoirsections occur in the Sikidang-Merdada area near wellsDNG-1, 4 and 12.
A shallower, thick permeability zone with trans-missivity on the order of 5 Darcy-meters has beenmeasured in DNG-8 at the Sikidang-Merdada area. InDNG-10 at Sileri the transmissivity value is about 12Darcy-meters in a thinner zone. At DNG-5 and 11 atPakuwaja the transmissivity is indicated as <0.2 Darcy-meters. Low transmissivity is also found at wells DNG-6 and 16 in Sikidang-Merdada area, where a dioriteintrusion was drilled from 1600m to total depth (2501mVD). Perhaps significantly this zone has a hightemperature (~320°C). The diorite could be related tothe heat source in this portion of the geothermal field.However, the distribution of this intrusion is not clearyet, even from the gravity data.
An interpretation of the permeability structure of theDieng reservoir is summarized in Figure 7, a crosssection of the permeability model developed forreservoir simulation by GENZL/SDB (1991). Thispermeability model indicates that lateral permeabilityat Sileri may be twice as high as that at Sikidang-Merdada.
DISCUSSIONS
Sections showing interpretative correlations between
the Sileri, Sikidang-Merdada and Pakuwaja areas aregiven in Figure 7. A tentative reservoir model wasdeveloped using borehole data, MT soundings andgravity measurements in order to delineate the deeperreservoir structures. At the Sikidang-Merdada area,a dome shaped steam zone caps a 320°C brinereservoir that contains 2000-3000ppm Cl and 0.5-1.6%vvt dissolved gas. This steam cap possibly covers theeastern and central part of the area. The westernpart is inferred to be brine dominated as demonstratedby the production of well DNG-7. Because high gasconcentrations have been measured in some wells, theupper reservoir zones may be rich in accumulated non-condensible gas. From downhole measurements andproduction data, the Sileri reservoir is interpreted asbeing two-phase and the Pakuwaja reservoir as singlephase liquid.
Figure 7 also shows two low permeability and lowtemperature barriers which separate Sikidang-Merdadaarea from the Sileri area in the north and from thePakuwaja area in the southeast. The southeast barrier,which is called the Kendil block, trends NE-SW and isprobably controlled by the F5 and F6 faults. Thegeophysical data show the block to be defined by agravity high and conductivity low. Well DNG-15 wasdirectionally drilled into this block and confirms itsexistence. The northern barrier, which trends E-W, isprobably controlled by the Fl fault. The existence ofthis barrier is based upon similar gravity and resistivityrelationships. The Fl fault, which is believed to be partof the oldest fracture system in Dieng, was intersectedby the productive well DNG-7. This evidence leads toan interpretation that the Fl fault has been reactivatedand is connected to the deeper higher temperaturebrine reservoir (>320°C).
It is interpreted that each prospective area has its ownupflow system, and they may be connected at a verydeep level where the barriers might disappear.
Based upon the relationships in Figure 7, a goodcorrelation might exist between well productivity, deepreservoir permeability, and the magmatic evolution ofDieng. These relationships are provided in Table 3.The areas underlying older volcanics, such as Sileri andSikidang-Merdada, are apparently more productiveand more permeable than areas beneath the youngervolcanics, such as the Kendil block and Pakuwaja. Butin general the permeability of the Dieng reservoir islow. One interesting feature of wells DNG-5 and 11 atPakuwaja is the existence of phyllic alteration in thesewells. Generally, phyllic alteration is associated withtemperatures >300°C, but at Pakuwaja measuredtemperatures only reach 290°C. This relationshipsuggests that Pakuwaja may be in cooling phase.
350
Well DNG-9 which was originally low in productivityand has now become unproductive penetrates the samepermeability structures encountered by wells DNG-1and 4 which were originally good producers. The lowproductivity of DNG-9 might be due to formationdamage which occurred as a result of lost circulation ormight be attributable to calcite and silica scaling.This well would be a good candidate for an acid jobfollowed by hydraulic fracturing in order to improvepermeability. Wells DNG-1, 4 and 7 (which was alsooriginally good producers), had to be abandonedbecause the casings are suffered from severe corrosiondamage. Poor cement jobs seem to contribute to thecorrosion problems by allowing shallow acidic fluids tocontact the casing. Cementing practices and the cementformula should be re-examined to overcome thisproblem.
The potential geothermal reserves of each of the threeareas have been calculated by multiplying the arealextent of the anomaly by two factors. The first factor isthe temperature differential, taken as the differenceof the measured reservoir temperature and a basetemperature, in- this case 180°C. The second factor,referred to as the "C" factor, is an energy conversionfactor with the units of MWe per area-temperature. Chas been given one of two values: 0.1 MW/°C km2 forenergy stored in fluid and 0.19 MW/°C km2 for energyin fluid and rock. That latter value is based uponexperience at the Kamojang geothermal field. Table 4shows the results of the potential reserve calculations.The largest reserves of up to 175 MW occcur in theSikidang-Merdada area. The total resource is estimatedto be as high as 355 MW.
Because the Sikidang-Merdada area has the highestpotential reserves, good well deliver ability (55 T/hr ofsteam from total flow of 75 T/hr per well), and 10 MWof existing capacity, this area is the most suitable for a55 MW development. In order to accelerate theresource develoment, the development plan should bechanged from the 1x55 MW unit to the followingcombination of units: 1x15 MW plus 2x20 MW. Thefirst 1x15 and 1x20 MW units should be fed byboreholes drilled in the eastern part of Sikidang-Merdada and the other 1x20 MW from the westernpart, as shown in the summary map in Figure 8.
Future exploration should be directed towardsthe Siglagah area. This area has both fumarolicmanifestations and a low gravity anomaly. At Dieng,the gravity anomalies are interpreted as a result of thickzones of argillic alteration. Based upon the size of theanomaly, Siglagah has an area of 2 km2 and up to45 MW of potential resource.
The high elevation area surrounding the Dieng Plateauis mostly composed of older volcanics, such as Gn.Prahu, Gn. Bisma, and Gn. Nagasari, which datebetween 2.5 - 3.6 million years. These older volcanicsprobably represent the recharge area for the Diengreservoir. The meteoric water could penerate thebasement rocks which are probably composed of marlor limestone.
CONCLUSIONS AND RECOMMENDATIONS
Provided below are the main findings and recommen-dations from this study.
(1) Drilling has defined three distinct, separateprospect areas at the Dieng field: Sileri, Sikidang-Merdada and Pakuwaja. A gravity anomaly andfumarolic manifestations suggest the existenceof a fourth prospect area at Siglagah. The totalpotential resource at Dieng is 355 MW, of whichthe Sikidang-Merdada area provides 175 MW.Barriers of low permeability and low temperatureseparate Sikidang-Merdada from Sileri andPakuwaja.
(2) The Sikidang-Merdada area has a dome-shapedsteam zone overlying the 320°C brine reservoircontaining 2000-3000 ppm Cl and 0.5-1.6% wtdissolved gas. The reservoir at Sileri is two phase,while Pakuwaja is single-phase liquid. All systemshave reservoir temperatures ranging from 280°C to>320°C. Reservoir modelling suggests that lateralpermeabilities at Sileri could be twice as high as atSikidang-Merdada. The permeability at Pakuwajais still unknown, but appears to be low, and anyfuture drilling at Pakuwaja should be considered asexploration holes.
(3) To accelerate commercial operation, a modularscheme consisting of 1x15 MW and 2x20 MW unitsis favourable for installation at Sikidang-Merdadarather than a single 1x55 MW unit. The 1x15 MWunit and a 1x20 MW unit should be fed byboreholes in the eastern portion of the area, andthe other 1x20 MW unit should be fed from westernwells. 10 MW of capacity currently exist, and eachfuture well is expected to supply 55 T/hr steam.
(4) DNG-9 is a good candidate well for an acid job andhydraulic fracturing in order to improve the well sproductivity.
(5) In general the Dieng field has low reservoirpermeability. In order to reduce formation damageby drilling mud, consideration should be given todrilling with aerated mud. Furthermore, many
351
wells at Dieng have experienced casing damage.To reduce well failures, investigations arerecommended for changing the composition of thecement and to setting the intermediate 13 3/8 inchescasing deeper to perhaps 750m.
ACKNOWLEDGMENTS
The authors express their appreciation to theManagement of PERTAMINA for allowing us topresent this paper. We also acknowledge D. Rohrs ofUnocal, who assisted with the English version of thispaper, and Djauhar Fuad, who helped preparing thepaper.
REFERENCES
BEICIP, 1975, Vulcanology of the Dieng Area,Indonesia, Internal Report, Lodged in PERTAMINAGeothermal Division.
Ganda and Suroto, 1985, Subsurface HydrothermalAlteration in the Dieng Prospect, Central Java,Internal Report, Lodged in PERTAMINA GeothermalDivision.
GENZL/PT. Sumber Daya Bumi, 1991, ComputerSimulation of the Dieng Geothermal Field, InternalReport, Lodged in PERTAMINA GeothermalDivision.
Fauzi,A., 1987, Mineralogy and Fluid Compositionat the Dieng Geothermal Field, Thesis, VictoriaUniversity.
Suwana,A., 1986, Chemistry of the Dieng GeothermalSystem, Diploma Report, Geothermal Institute,University of Auckland.
Unocal, 1989, The Dieng Geothermal Prospect,A Technical and Economic Assessment, UnocalGeothermal Division.
352
TABLE 1BOREHOLE DATA AND STATUS OF THE DIENG WELLS
WELLS
A. PRODUCTIVEDNQ - 2DNG - 8DNQ - 10DNQ - 13
B. NON PRODUCTIVE
1. Low T*KDNG-15
2. High T.Low KDNG-5DNG-11
3. BlockingDNG-3DNG-6DNG-9
4. AbandonedDNG-1DNG-4DNG-7DNG-12
C. NOT YET TESTEDDNG-14DNG-16
SIKIDANG - MERDADA
Depth(mVD)
16621806
1732
1905
195025012450
1901185524011996
17682283
BHT
275295
255
225
275300320
325325365325
250320
Dryness( x )
6355
70
Output(MWe)
3-2.5
>4
Sub Total >9.5
67
8090
-2-4.5- 2
-5.5-5.5-5.5-to
SILERI
Depth BHT Dryness Output(mVD) (°C) ( X ) (MWe)
2300 325 65 -3
Sub Total 3
Depth(mVD)
25002431
PAKUWAJA
BHT Dryness Output(°C) ( X ) (MWe)
Sub Total 0
285295
TABLE 2CHEMICAL ANALYSIS OF RESERVOIR FLUIDS AND HOT SPRING WATER
T. WAKNABII1NGANSILEIUNGANDAMPULASARIKALIANGETGARUNGWANARATA
pH
5.76.47.24.65.95.84.1
3.97
6.45.76.96.46.45.9
Na'
525164922956233518211062
73153123183249101259
K'
166478176891916193
116185760532427
Ca"
110894014040514883
1122721672261599059
Hg"
24176721
31032474815355117
HCOS'
34871
1054233663811
010434031320810604091053
cr
8023110373979674115391508
3915
386429439135388
S04=
370243119724288189450
6887152156451621483
sio2
19084834370
* Aft110280
3417517567
* ttA164. . 1
1242741
353
TABLE 3CORRELATIONS : PERMEABILITY, AGE AND PRODUCTION
A R E A
1. SILERICONTROLLED BY 1 WELL
2. SIKIDANO - HERDADACONTROLLED BY REP. 4 WELLS
3. KENOIL BLOCK(CONTROLLED BY 1 WELL)
4. PAKUWAJA(CONTROLLED BY 2 WELLS)
DEEPERPERMEABILITY
( mD )
Kx.Ky
30
15
< 4
NO DATA
KZ
5
5
0
NO DATA
A G E
( year )
460,000
370,000
190,000
90,000
AVERAGE WELLPRODUCTION
AT 15 BAR (T/h)
STEAM
35
55
TOTAL FLOW
65
75
NON PRODUCTIVE(Low K'tT)
NON PRO!(Low K, 1
WCTIVEUgh T)
TABLE 4POTENTIAL OF THE DIENG GEOTHERMAL FIELD
1.
2.
3.
4.
AREA ORPROSPECT
SIKIDANG -HERDADA
SILERI
PAKUWAJA'
SIGLAGAH
T O T A L
SIZE( km* )
6.5
3
2
2
POTENTIAL ( MWe )Q = C x A x A T
FLUID( C=0.1
90
40
30
25
185
)FLUID & ROCK( C=0.19 )
175
60
55
45
355
S Y S
STEAM CAP ANDCONTROLLED BY
TWO PHASE, T-CONTROLLED BY
HOr WATER, T-CONTROLLED BY
TWO PHASE, T-NEW TARGET
T E H
BRINE, T-320°C12 WELLS
32O°C1 WELL
320°C2 WELLS
300 °C
NOTE : Q = POTENIIAL (MWe)C = CONSTANCE OF CONVERSION FACTOR (HWe/°C km2)A = AREA ( km 2 )
A T = (T1-T2); T1 = RESERVOIR TEMPERATURET2 = CUT-OFF TEMPERATURE (180°C)
354
377,000 380,000S04
HCOi ClCHEMISTRY TERNARY DIAORAM
S O ,
Q, BI3MA
Modl f l td f r o m Ounawon I 9 6 8 , 0 t l o r u » 1 9 7 3 , Q o n d o 1964
LITH0L06ICAL UNITS
Hydrothermally altered rockVolcanic plainLava dome of G.SerojaQuartz latite of G. PokuwojoDacitic andesite lava of G. KendilAndesile of G. Merdada and PangonanAndesite of G. PagerkandangBasaltic andesrte of G.BismaAndesite of G. NagasariLava and tuffaceous breccia of G. Prau
AGE (million years)
0.070.090.190.370.462.532.993.60
Lava terrace
Volcanic cone
V 6 Well DNG 6/16
« Solfatara-fumarole
t Hot spring
t Mofete
FIGURE 1 - Geological map and fluids chemistry of the Dieng geothermalfield. Well locations are shown in this map, but Springs number6,7 and 8 are outside.
355
TO
60
SO
40
30
201510
SIKIDANG-MERDADA AREA70
10 20 3 2 40 SO 60 7075 80 90TOTAL MASS FLOW ( Ton/Hr)
70
^ «0
8} 40
3 s o
-J 20$ 15
10
TOTAL GAS <wt%>
2000 2200 Z4oo 2650ENTHALPY (KJ/KQ)
2800 40 60 7 0 80 100DRYNESS (%J
B
£
50
40
30
201510
SILERI AREA"u SO
10
,1 ,20 30 40 90 606570 80 90
TOTAL MASS FLOW (Ton/Hr)100
"•200 1400 1500 1600 1800ENTHALPY (KJ/Kg)
2000
iy 30
3 20
5 15
10
4 s ioTOTAL GAS (wt%)
15
20 40 50 60DRYNESS (%)
Note: No production data for Pakuwaja area
FIGURE 2 - Production characteristics of wells at the Dieng geothermal field.
356
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-0 --o-
-o--o-
—0- —0 —r
—i
10 15
year
2 0 25 3 0
2 0 0
FIGURE 3 - Prediction of gas concentration and steam flow changes up to 30 yearsproduction (1 x 55 MW) calculated from computer simulationmodelling for the Sikidang - Merdada area (after GENZL/SDB, 1991).
357
OOtfGOZ'6 000'002'6
000'S03'6 000'00Z'6
OO
"S6u99>E
2"53ISc
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360
TENTATIVE MODEL
-—S|NW—DIRECTION OF MAGMATIC MIGRATION ACCORDING TO THE AGE >
370,000 Ye 190,000 Yr 90,000 Yr
-—SE
•H \— —f-PAKUWKENDIL—f-PAKUWAJA AREA-*BLOCK .
SIKIDANG - MERDADA AREA{>"6.5km*)
T.MERMOAPP3lti20MWJ
| | Argllllc zoneI I Propjrlitlc zone
Phylllc zone
^Sedimentary basement3
Solfotara / fumaroltMoUttMain (e«d lontCotlng shoe 9^8 Inch
4 9Dlttanc* (km)
PERMEABILITY STRUCTURE10
1,600
RESIDUAL GRAVITY ANOMALY
M.T. TOTAL CONDUCTANCE
FIGURE 7 - The Dieng geothermal field cross sections.
361
376,000 380,000
SIGLAGAHrPROSPECT
SIKIDANGMERDADAAREA
Low K 6 T barrier
1 X 15 + 1X20 MW
1 X 20 MW
Power plant site
Well DNG6/16
PAKUWAUAAREA
FIGURE 8 - Prospective areas and sugested geothermal developmentat the Dieng field. Explanation for other symbols seefigure 1.
