o_-~~--- .---- Annual International Conference on Geological & Earth Sciences (GEOS 2012) Petrophysical analysis and organic geochemistry of Jurassic sediments in the Western Desert, E'gypt Mohamed,~agab Shalabyl, Mohammed Hail Hakimi2 and Wan Hasiah Abdullah2 Ipetroleum Geoscience Department, Faculty of Science, University of Brunei Darussalam, Brunei 2Departmentof Geology, University of Malaya, 50603 Kuala Lumpur, Malaysia mshalaby2004@yahoo,com Abstract- The petrophysical analyses and organic geochemistry have been evaluated for the Jurassic Formations, West~rn Desert of Egypt. The sandstones of the Khatatba Formation are characterized by fine to coarse-grained, moderate to well sorted, which deposited in fluvial channels and shallow-marine environments. The measured porosity and permeability proves the presence of good-quality reservoir rocks where maximum values are 17% and 1000mD respectively with no major diagenetic problems. The coal and shale sediments are characterised by high total organic matter and have good to excellent hydrocarbon generative potential. Kerogen type is predominantly type II-ill with type ill kerogen. The Khatatba source rocks are thermally mature and, at the present time, is within the peak of oil window with measured vitrinite reflectance values in the range of 0.81 to 1.08 Ro%. Therefore, it has been identified that the coals and organic-rich shale intervals are the most important source rocks while the sandstones are considered as the best good quality reservoir within the Khatatba Formation. Keywords- Petrophysical analysis, Organic geochemistry, Reservoir characterization, source rock, Egypt I. INTRODUCTION Recent hydrocarbon discoveries that have been made in the Western Desert of Egypt are thought to have significant exploration potential. The northern Western Desert, Fig. 1, still has a significant hydrocarbon potential as recent oil and gas discoveries have suggested [1] with as much as 90% of oil reserves and 80% of gas in the Western Desert's Basins yet to be discovered [2]. 31N 31N 29N Figure I. Location map of the study area Annual International Conference on Geological and Earth Sciences (GEOS 2012) Copyright @ GSTF 2012 155N; 2251-3361 doi: 10.5176/2251-3361_GEOS12.05 The area that forms the scope of this study lies in the northern Western Desert og Egypt between Latitudes 30° 30'- 31° 00' N and Longitudes 26° 30'- 27° 00' E. It is the most productive areas in the Western Desert and has attracted the interest of numerous researchers and oil companies for the exploration of hydrocarbons. The Western Desert contains sediments of Jurassic and younger age where the stratigraphic and tectonic setting have been studied in detail by several authors as in [3], [4]. Lithostratigraphically, the Khatatba Formation overlies the Ras Qattara Formation and underlies the Masajid Formation. The Middle Jurassic Khatatba Formation is formed by fluvio-deltaic clastics grading upwards into marine shales and limestones [5]. These sandstones are oil and gas reservoirs in some fields, whereas the coaly shale and shale facies represent the main hydrocarbon source rocks of the basin [6], [7], [8]. The coaly shales act also as seals, and thus the Khatatba Formation represents a typical hydrocarbon source- reservoir-seal system. II. RESERVOIR ROCKS AND PETROPHYSICS Based on core samples from wells in the study area,.the sandstones of the Khatatba Formation are fine to coarse- grained, moderately to well sorted quartzarenite deposited in fluvial channels and shallow-marine settings. It is also observed that the measured porosity values from core samples range from 1 to 17%, and measured permeability ranges from 0.05 to 1000 mD, Fig. 2. In the Khatatba Sandstones, the best reservoir quality rocks are characterized by medium to coarse- grained, good sorting with high percentages of detrital quartz and low percentages of matrix and cements. The formation is. .;< also affected by fracturing and dissolution of calcite cement J and unstable grains to enhance the petrophysical parametersi1 (porosity and permeability) Fig. 3. .~ 1000 100 .0 ;S 10 .c J" i': 5 1 ~ 0.1 0.01 0 10 Porosity (%) 15 20 Figure 2, Crossplot of porosity-permeability relationship 1 @2012GSTF~ , Ba from t Middl, most s high t< basin 1 with g [10]. ] shale vitrinit posses: Eval p hydrog . TOC P III ken the Mi, and ha' for hyd ....-- U 0 f- ;.t; -- S! ..... (:£ ,§. '" .g .: <:: <J e 2:;. - ,'" ] "'
Transcript
o_-~~--- .----
Annual International Conference on Geological & Earth Sciences (GEOS 2012)
Petrophysical analysis and organic geochemistry of Jurassic sedimentsin the Western Desert, E'gypt
Mohamed,~agab Shalabyl, Mohammed Hail Hakimi2and Wan Hasiah Abdullah2
Ipetroleum Geoscience Department, Faculty of Science, University of Brunei Darussalam, Brunei2Departmentof Geology, University of Malaya, 50603 Kuala Lumpur, Malaysia
mshalaby2004@yahoo,com
Abstract- The petrophysical analyses and organic geochemistryhave been evaluated for the Jurassic Formations, West~rn Desertof Egypt. The sandstones of the Khatatba Formation arecharacterized by fine to coarse-grained, moderate to well sorted,which deposited in fluvial channels and shallow-marineenvironments. The measured porosity and permeability provesthe presence of good-quality reservoir rocks where maximumvalues are 17% and 1000mD respectively with no majordiagenetic problems. The coal and shale sediments arecharacterised by high total organic matter and have good toexcellent hydrocarbon generative potential. Kerogen type ispredominantly type II-ill with type ill kerogen. The Khatatbasource rocks are thermally mature and, at the present time, iswithin the peak of oil window with measured vitrinite reflectancevalues in the range of 0.81 to 1.08 Ro%. Therefore, it has beenidentified that the coals and organic-rich shale intervals are themost important source rocks while the sandstones are consideredas the best good quality reservoir within the KhatatbaFormation.
Keywords- Petrophysical analysis, Organic geochemistry, Reservoircharacterization, source rock, Egypt
I. INTRODUCTION
Recent hydrocarbon discoveries that have been made in theWestern Desert of Egypt are thought to have significantexploration potential. The northern Western Desert, Fig. 1, stillhas a significant hydrocarbon potential as recent oil and gasdiscoveries have suggested [1] with as much as 90% of oilreserves and 80% of gas in the Western Desert's Basins yet tobe discovered [2].
31N 31N
29N
Figure I. Location map of the study area
Annual International Conference onGeological and Earth Sciences (GEOS 2012)Copyright @ GSTF 2012155N; 2251-3361doi: 10.5176/2251-3361_GEOS12.05
The area that forms the scope of this study lies in thenorthern Western Desert og Egypt between Latitudes 30° 30'-31° 00' N and Longitudes 26° 30'- 27° 00' E. It is the mostproductive areas in the Western Desert and has attracted theinterest of numerous researchers and oil companies for theexploration of hydrocarbons. The Western Desert containssediments of Jurassic and younger age where the stratigraphicand tectonic setting have been studied in detail by severalauthors as in [3], [4]. Lithostratigraphically, the KhatatbaFormation overlies the Ras Qattara Formation and underlies theMasajid Formation. The Middle Jurassic Khatatba Formationisformed by fluvio-deltaic clastics grading upwards into marineshales and limestones [5]. These sandstones are oil and gasreservoirs in some fields, whereas the coaly shale and shalefacies represent the main hydrocarbon source rocks of the basin[6], [7], [8]. The coaly shales act also as seals, and thus theKhatatba Formation represents a typical hydrocarbon source-reservoir-seal system.
II. RESERVOIR ROCKS AND PETROPHYSICS
Based on core samples from wells in the study area,. thesandstones of the Khatatba Formation are fine to coarse-grained, moderately to well sorted quartzarenite deposited influvial channels and shallow-marine settings. It is alsoobserved that the measured porosity values from core samplesrange from 1 to 17%, and measured permeability ranges from0.05 to 1000 mD, Fig. 2. In the Khatatba Sandstones, the bestreservoir quality rocks are characterized by medium to coarse-grained, good sorting with high percentages of detrital quartzand low percentages of matrix and cements. The formation is..;<also affected by fracturing and dissolution of calcite cementJand unstable grains to enhance the petrophysical parametersi1(porosity and permeability) Fig. 3. .~
1000
100
.0;S 10.cJ"i':5 1
~
0.1
0.01
0 10
Porosity (%)
15 20
Figure 2, Crossplot of porosity-permeability relationship
-Annual International Conference on Geological & Earth Sciences (GEOS 2012)
c' )'Pigure 3. Coarse grained sandstone indicating good porosity
Ill. ORGANIC GEOCHEMISTRY
aSed on the statistical summary of 52 samples collectedthe study area, the organic-rich shales and coals of theIe Jurassic Khatatba Formation has been identified as the
.~t'slgnificant.potential source rock. This is because of itsJittotal organIc carbon (TOe) content (1.0-32.5 wt.%) and
5~ill wide distribution, which meets the standard as a source''''''Ii,go.ciClto excellent hydrocarbon-generative potential [9],
Ii,Petrographic examination revealed that the coal and,sha.1e cuting samples consist predominantly of type IIIviti:initic and a mixture of type II-Ill liptiniticmacerals andqssess moderately to heavily stained with bitumen. Rock-yal pyrolysis analysis of the Khatatba source rocks show
q~yarogenindex (HI) values in the range of 63-261 mg HC/gTOC1Jrovingtype III kerogen (gas prone) and mixed type II-III kerogen (oil-gas prone) Fig. 4. At the present time, most ofthe Middle Jurassic Khatatba sediments are thermally matureand have entered the mature to late mature of oil window stagefor hydrocarbongeneration.
I II II ,, I, II <:.> I, = II 0 ,I '" ,I '" I, ~ ,, i;:t I, ~ II ". ,I ... ,I I ,I ..:: II - II ;;; II :: ,, <:.> ,I "0 I, = ,I 0 II U I, II ,,... I
IIII,,:Dry g'd.Swindow
ImmatUJ... Post-mature
gOOs~ Fa<-d.Tutn.ad..
100.TvpeIV-
ni .. - IV~oo >41n
I..,..430 - ~10
T m.. <"C)
Figure 4. Hydrogen Index vs Tma. showing kerogen typing
Based on our study, the reservoir characterization andorganic geochemistry have been carried out and conform thatthe Khatatba Sandstones were recognized as good reservoirquality and represent the main producing reservoir rocks. Thegood reservoir quality is deposited in a high energy fluvialdeltaic environment and mostly controlled by the compactionand pore occluding cements, where porosity and permeabilityhave been increased by leaching of the feldspar and dissolutionof calcite cement.. Regarding to maturity of source rock, thestudied samples indicate that the formation consists of coalsand organic-rich shales, revealing mainly type II-III and typeIII kerogen. Vitrinite reflectance data indicate the mature tolate mature stages of oil window for significant hydrocarbongeneration. The carbonate rocks of the Masajid Formation formthe regional seals in the basin and the coaly shale and shaleswithin the Khatatba serve as local seal. The overburden rocksperform sufficient levels of thermal maturity for hydrocarbongeneration.
ACKNOWLEDGMENT
The authors thank Khalda Oil Company, .Egypt forproviding the rock samples. Many appreciations are alsoextended to University of Malaya, and University of BruneiDarussalam for providing all facilities to complete this work.
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