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No. 1998.169

Geologic Setting and Petroleum System of Heavy Oil Occurrencesin Sedimentary Basins of India

P.K. Padhy and Daljit Singh, Oil Natural Gas Corporation, Baroda, India

Abstract

Heavy oil, in commercial quantity, has been on productionfrom a linear tectonic belt in the central Cambay Cenozoic riftbasin of western India. Recently heavy and nonbiodegradedoil has been discovered from the late Riphean-Vendian stratain Bikaner-Nagaur peripheral foreland basin situated to thenorth west of Indian shield.

Heavy oil belt of Mehsana sub-basin of Cambay rift liesclose proximity to the intrabasinal axial high (Mehsana horst)which has undergone synchronous episodic upliftment sinceearly-middle Eocene i.e., deposition of Cambay shale sourcefacies. Occurrence of heavy oil is confined to the pinch-outs ofthe post rift clastic sequence along the eastern peripheral partof the axial high and in an inversion structure, south-west ofMehsana horst.

Generation and migration of oil of Cambay-Kalol(!) petro-leum system ranges from Miocene onward. Depletion of n-alkanes of the high asphaltic oil, in contrast to the oil of thesurrounding fields, is probably due to mild biodegradation.The stable carbon isotopic study infers that oil is generatedfrom the source rock of low maturity at an early stage of cat-agenesis.

The Pan-African tectonism witnessed deposition of salt-anhydrite, carbonate and sandstone in Bikaner-Nagaur basin,analogous to that of Gulf, Oman petroleum province, alongthe primeval late Proterozoic rift. Oil is originated from lowthermal maturing source rock (Bilara dolomite) within anearly oil window. Early rift sediment (Jodhpur Sandstone)constitutes the primary reservoir facies. Heavy oil deposit ofBilara-Jodhpur (.) petroleum system is likely to be prevalentalong the basement controlled structures.

Introduction

Heavy oil play fairways have a selected geographic distribu-tion in Indian sedimentary basins. Since 1971 production ofheavy altered oils has been started from the fields of CenozoicCambay rift basin situated in the western India. The moderateimpedance heavy oil is found in the upper Eocene clastic res-ervoirs of north Cambay basin. The intragrabenal rift struc-tural dynamics played an important bearing on the alterationof oil sourced from lower Eocene Cambay shale.

Non-biodegraded heavy oil occurrence has been recentlydiscovered from Bikaner-Nagaur basin located in the north-western India. Study on paleogeography and paleotec-tonicset up infers that the basin could be regionally a part of exten-sion of Infracambrian Arabian platform. Interestingly pres-ence of bituminous shale, oil shale had been inferred quitelong back in this part

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from the Saline range of Infracambrianage.

Tectono-Stratigraphy of Cambay Basin

Cambay extensional expression is related to the evolution ofthe western continental margin of Indian plate which is char-acterized by a suite of rift system. The cambay rift initiation(Infrarift stage) took place during early Cretaceous alongNNW-SSE Dharwarian trend and the rift drift transition phaseof Indian plate witnessed volcanic event (late Cretaceous Dec-can Trap eruption) which is attributed to the movement ofIndian plate over the Reunion hot spot.

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The sinusoidal basinpropagation with low angle basin bounding listric fault arraysexhibits influence of oblique tensional/transtensionaldynamics

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representing a typical half graben style of basingeometry.

The asymmetrical rift development is associated with litho-spheric thinning, followed by subsequent reactivation of thepre-existing structural fabric. The 425 km long basin narrowstowards distal part inferring northward diminishment of riftpropagation. The normal geothermal gradient is of the orderof 35

°

C/km with North Cambay basin showing slightly highergradient.The thermotectonics and basin architecture resembleclose to the subcrustal mixed shear model in the basindevelopment

3

.

Tectono-stratigraphically the extensional basin segment isdivided into South Cambay basin comprising blocks namelyNarmada, Jambusar-Broach., and North Cambay basin con-sisting blocks such as Cambay-Tarapur, Ahmedabad-Mehsanaand Patan-Sanchor based on apparent change in tectono-depo-sitional style, demarcated by presence of orthogonal compart-mental cross strike faults/canjugate transfer zones across therift tract (Figure 1a). The geology of the basin is extensivelystudied by different workers.

4, 5, 6, 7, 8

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Onset of intensified rift propagation coincides concomitantwith the eruption of huge Deccan basalt during upper Creta-ceous time. The basin experienced four episodic rift relatedtectono-depositional systems viz infrarift systems tract, synriftsystems tract, postrift systems tract and late postrift systemstract. The initiation of basin subsidence was emplaced alongthe basin bounding listric/planar normal faults with the uplift-ment of basin margin. Tectonic subsidence along the highangle fault system fairly controlled the basin fill geometrywith distribution of minor-fault population, more intensetowards flexural margin. The basin is characterized by intraba-sinal highs/ridges, oblique to the rift axis. The prominentamong them is the Mehsana horst of Mehsana sub-basin/block. These intragrabenal highs have strong structural over-print on depositional events corresponding to later part ofearly Eocene synrift regressive sequence in the north Cambaybasin, Mehsana sub-basin in particular. Tilting of fault blocksand synchronous horsting subsequently caused alteration ofoil entrapped in the structure close vicinity to the high.

Distinct phase of episodic rift propagation resulted charac-teristic linked tectono-depositional systems, over Deccan trap(acoustic volcanic basement), separated by basin-boundunconformities.The basin witnessed the regional marine trans-gression during early Eocene time depositing Cambay shalesource facies. Extensive middle Eocene sediments weredeposited by the south westerly flowing principle fluvial sys-tem in different tectonic blocks along the topographic lowsduring postrift phase. Ankleshwar formation (South CambayBasin) and Kadi and Kalol formations (North Cambay basin)of middle Eocene age are the main petroliferous stratigraphicunits. The homotaxial equivalent of Younger Cambay Shale ofsouth Cambay basin is characterized by development of threemain regressive units known as Kadi formation (Figure 2) inthe North Cambay basin. Basin-scale transgression prevailedduring late Eocene/early Oligocene time depositing Tarapurshale which constitutes the regional cap rock facies. Towardsthe end of thermal sag stage, the basin experienced reversetectonism, with adjustment of original extensional stress field,resulting forced folding and other anticlinal arching. Thehydrocarbon migration occurred during early Miocene coin-ciding with the terminal phase of basin inversion.

Mehsana Horst, Its Control on Depositional Events and Hydrocarbons (Heavy Oil) Accumulation

Geographically the main heavy oil fields (Lanwa, Balol, San-thal, and N.Kadi) constitute as a linear belt (Figure 1B) on thelowside of the fault block to the east of Mehsana Horst.Bechraji field, situated to the south-west of the MehsanaHorst, constitutes a mild inversion structure for entrapment ofoil.

Mehsana horst constitutes one of the prominent intragrabe-nal positive features in Mehsana sub-basin (Figure 3) separat-ing two half grabens — Warosan low to the east and Bechrajilow to the west. Seismic expression of rift structural style ofMehsana sub-basin exhibits the aggrading reflector close tothe rift shoulder representing the footwall derived sequence ofearlyrift stage. The fault — controlled subsidence continuedduring synrift time with rotation of fault block as evident fromthe divergent stratal package towards hanging wall fault plane,to the west of Mehsana horst, thus giving rise to asymmetrygeometric configuration. The gentler dip package of reflectorover the steep ones infers diminishing effect of rotationaleffect with younger events onlapping over it (Figure 3). Thebasin-dip divergent reflectors close to the east of Mehsanahigh during synrift time infers out passing of fault-controlledsubsidence over sediment supply. The fairly lateral continuityof reflector package close to basin-dip is attributed to nearequilibrium condition. The parallel onlapping fill reflectors(Figure 3) constitute the postrift sequence represented byupwarping folded features. Heavy oil entrapment of Lanwa,Balol, Santhal and Bechraji is confined to upwarping struc-ture, resulted during basin inversion period.

The deposition of sandstone-shale with strong coalcyclothem during the period of middle to early Eocene timetowards basinal low and uplifted terrace/ramp part is attrib-uted to prevalence of humid climatic condition under theinfluence of relatively slow rate of basin subsidence. TheKalol reservoir facies pinchout on either side against the epi-sodic rise of the Mehsana high.

Paleotectonic analysis

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and crestal thinning of youngerstratigraphic units over the high with downflank thickeningfairly confirm its synchronous upliftment (Figure 4) sinchearly Eocene time due to episodic rejuvenation and rotation ofconjugate listric faults. Presence of asphalt filled fractureswithin Cambay shale over the Mehasan high is an indirect evi-dence of contemporaneous upliftment. It remained as positivefeature till late Eocene time and subsequently inundated bybasin wide marine transgression during Oligocene depositingTarapur shale (regional seal rock) over the high.

The episodic upliftment imparted a sort of tectonic barrierfor the westerly major paleo run-offs during later part of earlyEocene

10, 9

. Evidently the parallel stratal configuration of con-siderable thickness (primarily sandstone-shale-coal facies oflater part of early Eocene) in the east of Mehsana high isclearly seen where as it is poorly present to the west. The prin-ciple fluvial system mainly got restricted to the eastern part byMehsana Horst. Thus it created a two apparently marked tec-tono-sedimentary environment on either side of the horst. Itwas only during later part of middle Eocene (near dormantstage of Mehsana high reactivation) the fluvial system corre-sponding to the upper part of Kalol formation could prevail oneither side of the high depositing sandstone-shale and minorcoal.

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Cambay-Kalol(!) Petroleum System

Occurrence of heavy oil is confined to Kalol formation alongthe linear belt close to the east of Mehsana horst and Bechrajified. Cambay Shale of Paleocene -early Eocene represents theprimary source rock (Figure 5), deposited during synrift stageof basin evoluation. Based on an identified unconformitymarker and geochemical characteristics of sediments CambayShale is divided into two members: Older Cambay Shale andYounger Cambay Shale, the latter is characterized by threeprominent deltaic sequences (sandstone-shale-coal) separatedby marine shale. In Mehsana block the thickness of OlderCambay Shale ranges from 200–800m. The organic matter ismainly type-III kerogen and organo facies deposited towardsbasinal axis is characterized by type-II kerogen. TOC in Cam-bay Shale ranges from 2–4%. The burial history analysis (Fig-ure 6) shows onset of oil generation took place since earlyMiocene time. The associated events/processes are depicted inFigure 7. The carbon isotope of aromatics and saturates plot(Figure 8) infers high proportion input of terrestrial organicmatters in the source rock. Hopane and sterane biomarker dis-tribution indicates that the heavy oil belt of Lanwa - Balol —Santhal is abundant of C29 sterane (Figure 9). High ratio ofhopane to sterane (11–24) indicates terrestrial sourceorganics

11,12

and in contrast, predominance of C30 steranehomologues in heavy oil of Becharji field (Figure 9) inferslacustrine algal input in the source facies deposited in Bechrajilow. Biomarker fingerprints (Figure 10) of heavy oils showcharacteristics of similar terrestrial source organics. Paleogeothermal gradient of North Cambay basin is 35–50° C/km.The average TOC, S2 and HI value of Cambay shale sectionmet in the well drilled in the basinal part is 3.95, 5.6 and 116,and that of in Bechraji field is 0.9, 0.34, and 35. In the northCambay basin the maximum hydrocarbon generated (HCG) inCambay shale is of the order of 4 million MT/Km.

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Kadi and Kalol formations represent the principle clasticreservoir facies in Mehsana block. The litho assemblage ischaracterized by sandstone — coal — carbonaceous shalesuite deposited under paludal environment.The heavy oiloccurs at a relatively shallow depth (-800 to -1050mts) and isconfined to the upper part of Kalol formation (Kalol sand-Iand II, Upper Suraj Pay of Wavel member which pinch-outsagainst the Mehsana Horst. The thickness of each payzoneranges from 4–20 mts., porosity and permeability are of theorder of 20–30% and 3–5 darcy.

The level of certainty infers the confidence level in oil to aparticular active source rock. GC-MS, carbon isotopic andbiomarker data of oils and source rock extracts

11, 12, 14

fairlyshow presence of good correlation between oil and Cambayshale source rock. Carbon isotopic composition of aromatics(ranges from - 29.4 to -31.6) of heavy oil indicates goodmatch with the value of Cambay source sediments (-26.1 to -29.8) and carbon isotopic ratios saturates versus of aromaticsof heavy oil and rock extracts of Cambay shale show nearsimilarity (Figure 8). The C29R/C30R sterane ratio (1.0-2.3)

is well correlated with the higher sterane rich (0.98 - 2.03) ofCambay shale.

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Also hopane/sterane ratio (11.0-23.4) ofheavy oil exhibit close correlation with that of sedimentextracts (8.5-28.3) of Cambay shale.

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Petroleum Geochemistry of Heavy Oil: A Degradational Model

Oils from the fields (Lanwa, Balol, Santhal, and N. Kadi andBechraji) are asphaltic, heavy (0.93–0.97) and aromatic (Satu-rate: aromatic ratio = 0.57-1.53) in contrast to the oils of thesurrounding fields. The oil occurs at a shallower depth withinthe Kalol formation. Chromatographic signature of these oilsare distinguished by complete absence of n-alkanes (Figure11) with partial absence in the oil of North Kadi field situatedsouth of the elongated homoclinal linear heavy oil belt.

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Devoid of n-alkanes, reduced isoprenoids and absence ofalkylcyclohexanes (Figure 12) indicate the oil might haveundergone biodegradation.

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Carbon isotopic composition ofsaturate and aromatic fractions of heavy oil ranges from -31.0to -33.0 and -29.4 to -31.6 respectively.

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The associated gas,rich in methane (95–99%) and with high ic4/nc4 ratio (4–6), ischaracteristics of thermogenic in nature.

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The lighter

d

13c saturates support low maturity of sourcerock. Biomarker study reveals that hopane isomerisation hasreached equilibrium stage

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inferring generation of oil hasentered the oil window (Ro > 0.55). The low value of C29sterane isomers viz, 20S/20R and

b/a+b

shows comparativelylow maturation level of heavy oils

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and generation of oil froman early catagenetic stage.

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Absence of n-alkanes does not mean always immaturity.The Kalol oils close to Mehsana Horst is heavy, viscous andasphaltic in nature and GC of the heavy oil pyrolysates resem-bles with that of well preserved oils of the surroundingfields.

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Hence absence of n-alkanes could be due to biodegra-dation/water-washing.

Interestingly the synchronous horsting continues uptoMiocene, predating/contemporaneous with the hydrocarbonmigration time. The uplifted structure slopes southward withgradual diminishing of horsting and it has been observed thatthe degree of alteration of oil increases towards north alongthe linear belt (Figure 13). It has been observed that oil viscos-ity also increases towards north (60 cp in Santhal, 150 cp inBalol and 600 cp Lanwa field). Possibly the upliftment hasestablished an hydrostatic head to drive meteoric water andthere by altering the oil. Presence of thermophillic micro-organisms in the formation water has also been observed

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Structurally controlled high relief is characterized by heavyoil in this region. The hydrogeochemistry study

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has alsoindicated the recharge of meteoric water causing alteration ofoil.

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Tectono-Stratigraphy of Bikaner-Nagaur

Bikaner-Nagaur basin constitutes a late Riphean-Vendianbasin in the north western part of peninsular Indian shield.The tectonic tract of Rajasthan shelf comprises Bikaner-Nagaur, Jaisalmer, and Barmer basins. Structurally ikaner-Nagaur basin is bounded in the east by Delhi- Aravalli foldingand in the south, south-west by Pokra -Nachna high, separat-ing Jaisalmer basin and to the north-east lies the Delhi-Sar-goda ridge (Figure 14). The basin slopes to north and north-west and merges with the Indus shelf. The north-westernshield (Rajasthan craton) had undergone proto-plate tectonics:a complex process of a Proterozoic accretionary collisionaltectonics starting from 1300–700 ma

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. This accretionary pro-cess, with the development of trench-arc-marginal sea pro-grading westward, continued and the remnants are representedby suite of ophiolite melange. The collided subduction tecto-gen caused wide spread volcanic suite (Malani lgneous suite)of calc-alkaline

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which constitutes the basement of Rajasthanshelf. The Pan-African extensional tectonism witnessed depo-sition of synrift evaporite along the late Proterozoic rift (Ara-bian Infracambrian salt basin set up).

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The Bikaner-Nagaurbasin could probably an extension of the Infracambrian tec-tono-depositional system (Figure 15) of Arabian platform

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.The major tectonic element is represented by basement highstrending meridional to submeridional direction, the prominentbeing the Pokran-Nachna high to the south-west. These couldbe related to basement block faulting with langitudinal basinallows depositing maximum sediment thickness of around2,000 mts. The prominent east-west basement high trend actsas a structural trap for heavy oil accumulation (Figure 14).

Broadly two sedimentary systems (a) clastic-carbonate sys-tem (Infracambrian-Cambrian) (b) Clastic dominant system(Post Devonian). have been observed in this basin (Figure 16).The synrift clastic-carbonate system is correlated to the Saltrange of Punjab basin and Harmuz of Gulf.

Early Synrift Fluvio-Clastic Cycle: comprises of conglomer-ate, arkosic sandstone with minor shale and volcano-clasticfragments of Vendian age. The Jodhpur formation is uncon-formably underlain by Malani lgneous Suite and overlain byBilara formation.

Synrift Carbonate-Evaporite Cycle: The carbonate sedimenta-tion corresponding to Bilara formation is deposited undershallow marine transgressive phase. The limestone is oftenstromatolitic in nature. It is overlain by evaporite sequence(Hanseran Evaporite formation)

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, and laterally it can be cor-related to Ara evaporite of Oman.

Postrift Clastic Cycle: During lower Cambrian time, thereseems sharp change in facies from carbonates to clastics (con-glomerate, sandstone) deposited under high energy shallowwater condition. The clastic dominated Nagaur formationgrades upward to second cycle of carbonate-evaporite sedi-mentation.

Permo-Triassic Fluvio-Glacial Cycle: The basin experienced astrong regional upliftment during post-Cambrian and it

remained emergent and non-depositional during Ordovician,Silurian and Devonian periods. The basin bound fault systemgot reactivated during Permo-Triassic time with deposition ofconglomerate, gritty sandstone, chert with minor cherty dolo-mite (Bap and Badhaura formations). The faunal assemblagesis correlated with Eury desma and Conularia beds of Saltrange.

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The basin floor underwent north westerly tilting withthe development of prominent Pokran-Nachna high. The basinremained uplifted for a considerable time during Mesozoic.

Jurassic — Cretaceous Fluvio-Deltaic Cycle: The subsurfacegeological data from the drilled well infers the Jurassic sedi-ments (red brittle sandstone, pinkish ferruginous sandstone)unconformably overlies the Bap and Badhaura formation. TheJurassic sediments are overlain by a thin sequence of darkgrey claystone with minor sandstone of Maestrichtian age sed-iments.

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Tertiary Cycle: Consequent to the upliftment during upperCretaceous — lower Paleocene time (initiation of Himalayancollision phase), the western Rajasthan shelf had a widespreadmarine regression during Paleocene with deposition of con-glomerate, sandstone (Palana, Marh formations). EarlyEocene marine transgression occurred with advancement ofthe sea in Bikaner-Nagaur basin depositing Jogira limestone.The Quaternary deposit mainly constitutes clay, claystone,sandstone.

Bilara — Jodhpur (.) Petroleum System

Scope of prevalence of Proterozoic petroleum and petroleumsystem in Indian sedimentary basins

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has remained as anenigma in exploration history. Occurrence of asphaltene richoil has been discovered from late Riphean-Vendian-Cambriansequence in the newly explored Bikaner-Nagaur basin.

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Geochemically the oil characteristics fairly match with theInfracambrian oil of Huqf group of central Oman and Saltrange of Pakistan.

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The GCMSMS data

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infers origin of oil from Vendian -Cambrian carbonate source deposited under marine environ-ment. Limestone of Bilara formation and Upper Carbonatesequence (Cambrian age) are generally massive and dolomiticin nature. Thickness of Bilara formation ranges from 50–55mts. The dolostone is deposited under shallow marine envi-ronment and is associated with minor amount of chert andanhydrite nodules.

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The TOC content of Bilara dolostone ismoderate to high (up to 400 mg HC/ of TOC) and the hydro-gen indices is of typical oil prone algal rich organic matter.

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Low sterane / hopane ratio (0.38) and highly negative stablecarbon isotope ratio infer oil originated mainly from phy-toplanktonic organic matter deposited under restricted marinewith significant bacterial input.

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Low diasteranes/ diaster-anes+steranes), low Ts/Tm and moderately high gammacer-ane (Figure 17) suggest carbonate-evaporite source.

26

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The oil is nonbiodegraded as evident from the abundantpresence of n-paraffins and acyclic isoprenoids (Figure 18).Low aromatic steroid (22%), low gravity oil (17.6 API), highsulfur rich (1.2 wt%), high Pr/nc17 (0.91) and Ph/n18 (1.0)ratio of oil indicate that it originated from a low thermal matu-rity source rock within the early oil window.

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Within Infracambrian sequence, heavy oil occurs in sand-stone reservoir of Jodhpur formation at a shallower depth(1,100m). Patches of heavy oil occurrence is also observed insiltstone of Hanseran evaporite sequence and within vugs andfractures of carbonate reservoir of Cambrian age.

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The oil isasphaltic in nature (asphaltene content is 42%) and is viscous(6,667 cp at 30°C). Jodhpur sandstone is arkosic, course tofine grained with small scale cross bedding and depositedunder braided river environment. Porosity of sandstone reser-voir ranges from 16–25%.

Entrapment style is mainly structural controlled basementhighs and it is envisaged that the heavy oil is accumulatedmainly in the reservoir rocks deposited on these highs. Asthere is a prolonged hiatus in post Cambrian (Ordovician-Sil-urian-Devonian) time, it is presumed that trap might haveformed during synrift stage with critical moment taking placearound mid Cambrian time21 (Figure 19). The evaporitesequence, deposited under restricted environment, (supratidal)acts as an effective seal and this can be regionally correlatedwith the evaporite sequence of Salt range of north Pakistan,Harmuz of Gulf basin and Rezu-Desu-Ravan series of Kermanbasin of central Iran.

Presence of Infracambrian heavy oil has been inferred fromone well in this basin, and based on regional correlation of theoil of Arabian platform, it is inferred that the source could beVendian / Cambrian carbonates. Moreover age — diagnosticbiomarkers (high 24–isopropyl/ n-propylcholestane ratio > 1)infer oil sourced from Vendian to early Cambrian rock.

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Conclusion

Heavy oil fairways of Mehsana block of Cambay basin isbasically controlled by episodic rejuvenation of intrabasinalstructural high (Mehsana horst). The habitat of heavy oilpetroleum system of Eocene age has both geographical andstratigraphic limitations. Geochemical analysis infers terres-trial inputs in source organics. Absence of n-alkanes andreduced isoprenoids in oil indicates that it might have under-gone biodegradation/waterwashing. The synchronous uplift-ment with rejuvenation of conjugate fault systems possiblydrived meteoric water, thus altering the reservoir oil.

The discovery of upper Proterozoic petroleum system ofBikaner-Nagaur basin establishes the possible continuation oftectono-depositional salt basin set up of Arabian plate. Thesedimentary system is primarily classified as synrift carbonate— evaporite cycle and post rift — clastic dominant cycle. Theheavy, low thermal maturity, nonbiodegraded oil occurs inearly synrift clastics and it is generated from carbonate source

rock deposited in anoxic marine environment. The evaporitesequence acts as an ideal cap rock for entrapment of oil. It isenvisaged that the basement high trends along the evaporitedepositional locales could be the possible geographic exten-sion of prevalence of Infracambrian petroleum system in thenorth western basinal part of the Indian shield.

Acknowledgment

The authors record their gratefulness to the Director (Explora-tion) for according permission for publication of the paper.

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Figure 1A: Location Map of Cambay Basin

Figure 1B: Location Map of Heavy Oil Fields of Mehsana Block

Figure 2: Techno-Stratigraphy of North Cambay Basin

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Figure 3: Seismic Section Showing Major Tectono-Depositional Elements

Figure 4: Seismic Paleotectonic Evolution of Mehsana Horst and Mild Basin Inversion

9

Figure 5: Schematic Geological Cross Section of Cambay-Kalol Petroleum System

Figure 6: Burial and Thermal history of a Well close to Wardsan Low

10

Figure 7: Events Chart for Cambay-Kalol Petroleum System of North Cambay System

Figure 8: Carbon Isotopic Ratio of Saturate versus

Aromatic Hydrocarbons in Heavy Oils and

Rock Extracts from Cambay Shale

Figure 9: Predominance of C

29

Sterane Homologues in Heavy Oil

Belt: Bechraji Well Oil (BX-6) Shews Abundance of C

3011

11

Figure 10: Triterpane Distribution of Heavy Oil

From M/Z 191 Mass Fragmentograms

11

Figure 11: G C Fingerprints of Heavy Oil

15, 11

Figure 12: Mass Fragmentograms of

Alkylcyclohexanes (M/e 83) of Heavy Oils

15

Figure 13: Oil Gravity (Kalol Formation) Against Depth

Figure 14: Sedimentary Basins and

Tectonic Elements of Rajasthan

Figure 15: Paleogeography of proterozoic

Sediments of Indian Plate

21

12

Figure 16: Tectono-Stratigraphy of Bikaner-Nagaur Basin

Figure 17: Terpane Mass Chromatogram for Saturate Fraction of Well-A Oil Bikaner-Nahgaur Basin

26

13

Figure 18: Gas Chromatogram of Well-A Oil, Bikaner-Nagaur Basin

26

Figure 19: The Events Chart for Bilara-Jodhpur Petroleum System of Bikaner-Nagaur Basin

21