Organic-geochemical-characteristics-of-crude-oils-and-oil-source-rock-correlation-in-the-Sunah

Organic geochemical characteristics of crude oils and oil-source rock correlation in the Sunah oil ?eld,Masila Region,Eastern Yemen

Nabil M.Al-Areeq a ,*,Abubakr F.Maky b

a Department of Geology and Environment,Faculty of Science,University of Thamar,Yemen b

Egyptian Petroleum Research Institute (EPRI),Nasr City,Cairo,Egypt

a r t i c l e i n f o

Article history:

Received 8October 2014Received in revised form 27December 2014

Accepted 6January 2015

Available online 17February 2015Keywords:Crude oil Biomarker

Depositional environment Source inputs Sunah oil ?eld Masila Region

a b s t r a c t

The objective of this study is to provide information on source organic matter input,depositional conditions and the correlation between crude oils recovered from Sunah oil ?eld and Upper Jurassic Madbi Formation.A suite of twenty-six crude oils from the Lower Cretaceous reservoirs (Qishn clastic)of the Masila Region (Eastern Yemen)were analysed and geochemically compared with extracts from source rock of the Upper Jurassic (Madbi Formation).The investigated biomarkers indicated that the Sunah oils were derived from mixed marine and terrigenous organic matter and deposited under suboxic conditions.This has been ach-ieved from normal alkane and acyclic isoprenoids distributions,terpane and sterane biomarkers.These oils were also generated from source rock with a wide range of thermal maturity and ranging from early-mature to peak oil window.Based on molecular indicators of organic source input and depositional environment diagnostic biomarkers,one petroleum system operates in the Masila Region;this derived from Upper Jurassic Madbi organic-rich shales as source rock.Therefore,the hydrocarbon exploration processes should be focused on the known location of the Upper Jurassic Madbi strata for predicting the source kitchen.

?2015Elsevier Ltd.All rights reserved.

1.Introduction

The Masila Region,an oil-rich area and has become the biggest oil producing part of the Syun-Masila Basin in Eastern Yemen (Fig.1).The dataset used in this study are taken from the most productive Sunah oil ?eld in the Masila Region,which it is located onshore and occupy the northeast part of the Masila Region (Fig.1).The Masila Region is situated within the Upper Jurassic-Lower Cretaceous Sayun-Masila rift basin and contains several produc-ing oil ?elds of various sizes,the largest of which are the Cammal,Haijah and Tawilah oil ?elds (Fig.1).In 1990,the Canadian Oxy Oil Company discovered oil in the sandstone intervals of the Qishn Formation in the Masila Region,which the Sunah e 1well was the ?rst exploration well drilled in the Masila Region.The next prospect drilled was Haijah ?eld,25km to the south of Masila Region (Fig.1).Haijah e 1well was reached a total depth to the basement rocks into oil bearing sand of Lower Cretaceous Qishn Formation (Al-Areeq,2008).Canadian Oxy Company declared the Masila Region as commercial area in 1991and started production began in July 1993.The total known oil-in-place exceeds 1.6billion STB,with proved

ultimate recoverable oil reserve approaching 900million STB and the reserve estimates (Proved,Probable and Possible)are in excess of one billion of recoverable oil.The main producing reservoirs in the Masila oil ?elds occur in the Lower Cretaceous Qishn Formation.Oil also is found in another Lower Cretaceous and Middle to Upper Jurassic clastic and carbonate reservoir rocks,as well as fractured granitic basement rocks.The geochemistry and hydrocarbon po-tential of the Masila oil ?elds have previously been studied by a number of researchers (e.g.,Mills,1992;King et al.,2003;Hakimi et al.,2011a,b;Al Areeq et al.,2011).The present paper reports the results of an investigation on crude oils and the potential source rock recovered from the Sunah oil ?eld.The objective was to use biomarker distributions to characterize the oil types and to assess the respective depositional environment,age and thermal maturity of their potential source rocks.Furthermore,the molecular composition results from both the oil and source rock samples allowed for an oil e source rock correlation.2.Geologic setting

The Masila oil ?elds are situated within the Sayun-Masila rift Basin,which are the most productive oil ?elds in the Sayun-Masila Basin (Fig.1).The stratigraphic section in the Sayun-Masila Basin

*Corresponding author.

E-mail address:nabilalareeq@befca13281c758f5f71f6704 (N.M.

Al-Areeq).Contents lists available at ScienceDirect

Marine and Petroleum Geology

journal h omepage:ww befca13281c758f5f71f6704/l ocate/marp

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Marine and Petroleum Geology 63(2015)17e 27

ranges in age from Proterozoic to Tertiary and can be subdivided into three megasequences:pre-rift (Proterozoic to mid-Jurassic),synrift (mid-Jurassic to earliest Cretaceous)and post-rift (earliest Cretaceous and Tertiary;Fig.2).Pre-rift megasequence ranges in age from Proterozoic to mid-Jurassic (Fig.2).The basement of the Sayun-Masila Basin consists mostly of igneous and metamorphic complex rocks of Proterozoic to early Cambrian age.Pre-rift sedi-mentation is represented by mostly continental deposits of the Kuhlan Formation (Fig.2);this formation includes ?uviatile and arkosic red beds that grade upward into a shallow-marine facies and represents the early transgressive phases of the Late Jurassic seas (Beydoun et al.,1998).These continental rocks are overlain by shallow marine fossiliferous carbonates such as the Shuqra For-mation of the Amran Group (Fig.2).The Upper Jurassic Shuqra Formation conformably overlies the Kuhlan Formation with a gradational contact.It conformably underlies the Madbi Formation (Fig.2).The Shuqra Formation is a neritic limestone with richly fossiliferous marls and does not contain potential source beds (Beydoun et al.,1998).

The syn-rift sequence is characterized by horsts and nested fault blocks that were developed during Late Jurassic to Lower Creta-ceous time (Redfern and Jones,1995).Syn-rift sections of the Madbi and Naifa formations were deposited during the Jurassic in marine settings in the structurally lowest areas (Smewing,1997;Smewing et al.,1998).During the Late Jurassic commencing in the Kimmer-idgian,syn-rift sediments of the Madbi Formation were deposited (Beydoun et al.,1998).The Madbi Formation is composed of porous lime grainstone to argillaceous lime mudstone (Beydoun et

al.,

Figure 1.Main sedimentary basins of Yemen and regional tectonic elements (modi ?ed after Beydoun et al.,1998),showing the Masila oil ?elds including ten exploration wells presented and provide core and well log data of the Qishn clastic.

N.M.Al-Areeq,A.F.Maky /Marine and Petroleum Geology 63(2015)17e 27

18

1998).The lithofacies of this unit re ?ects an open marine envi-

ronment (Beydoun et al.,1998;Hakimi et al.,2012a,b ).The upper

part of Madbi Formation is composed of laminated organic rich

shale,which is considered to be a proli ?c source rock in the Syun-

Masila Basin (Mills,1992;King et al.,2003;Hakimi et al.,2010,

2011a,b;Al Areeq et al.,2011).During latest Jurassic to Early

Cretaceous time,the rifting system of the Syun-Masila Basin

continued,but the subsidence became slower.It was accompanied

by the accumulation of carbonates in shallow marine shelf deposits

(Naifa Formation).In Early Cretaceous time,sea level rose on

relatively ?at ground,resulting in marine transgression and sedimentation of widespread shallow marine carbonates (Saar Formation).The Saar Formation is composed mainly of limestone,dolomitic limestone with some mudstone,and sandstone.Oil companies classi ?ed this formation into lower Saar carbonate and upper Saar clastic.The lower unit of the Saar is characterized by the predominance of limestone,dolomite,mudstone and marl.Mean-while,the upper part is mainly sandstone and dolomitic limestone facies (Canadian Oil Company,“personal communication ”).The post-rift represents late Early Cretaceous to Tertiary time and rests unconformably on the syn-rift befca13281c758f5f71f6704te Early Creta-ceous sediments,known as the Qishn Formation,consist of

braided Figure 2.Lithostratigraphic section of the Sayun-Masila Basin (Compiled and modi ?ed after Beydoun et al.,1998;King et al.,2003).

N.M.Al-Areeq,A.F.Maky /Marine and Petroleum Geology 63(2015)17e 2719

plain to?uvial and shallow marine sediments deposited in the Syun-Masila Basin.The Qishn Formation is divided into two members,upper Qishn carbonate and lower Qishn clastic members. The lower Qishn clastic member is considered the main reservoir in the Syun-Masila Basin and comprises over90%of recoverable oil in the basin(Canadian Oil Company,“personal communication”).The upper Qishn carbonate member constitutes an excellent seal to the underling lower Qishn member reservoir and consists of laminated to burrowed lime-mudstone and wackestone interbedded with terrigenous mudstone and black?ssile shales.These sediments were deposited in deep water under alternating open and closed marine conditions(Beydoun et al.,1998).

During the late Early Cretaceous,alternating regression and transgression occurred.This pattern developed clastic(Harshiyat Formation)and carbonate rocks(Fartaq Formation)interbedded with each other.A similar pattern of sedimentation occurred in Upper Cretaceous time,where?uvial systems(Mukulla Formation) prograded southeast ward in the basin.The Late Cretaceous Shar-wayn Formation deposits are composed mainly of shale.In the Late Paleocene,sea level rose and resulted in the formation of trans-gressive shale deposits(Shammer Member)at the base of the Umm Er Radhuma carbonate formation.The Umm Er Radhuma Forma-tion consists of limestone(hard to medium)interbedded with thin layers of white to brown microcrystalline dolomite and is in?u-enced by the unconformity between the Cretaceous and Tertiary sequences.It is overlain by shale(Jiza’Formation).Jiza’deposits are widespread in the Early Eocene followed by the deposits of the anhydrite rocks(Rus Formation).

3.Pervious source rock studies

The Madbi Formation(Kimmeridgian age)was identi?ed as the major source rock unit and its source rock character was expected to be regionally extensive throughout the Syun-Masila Basin (Hakimi et al.,2010,2011a,b).Madbi shale(organic-rich shale) sequence was established as the dominant source sequence for the northern as well as southern oil?elds of Masila Region(Al-Areeq et al.,2011).These studies showed that good oil-source rock po-tential of the Madbi shales as suggested by high values of total organic carbon content(TOC>3.0wt%).The kerogen typically has a relatively high hydrogen index(HI),ranging from302to834mg HC/g TOC,and low oxygen index,ranging from5to52mg CO2/g TOC,indicating predominantly type II with minor type I,derived from algal marine organic matter(Hakimi et al.,2011a,b;Al-Areeq et al.,2011).This is in agreement with the petrographic results discussed in Hakimi et al.,2012a.Madbi shale strata penetrated in the most wells throughout the oil?elds in the Syun-Masila Basin with signi?cant of thickness in the range of30e100m.The Madbi shales have entered early-mature to peak mature and oil genera-tion began during the Late Cretaceous and Middle Miocene (68.17e15.12Ma),and reached a maximum during the Paleocene (15.12Ma)(Al-Areeq et al.,2011).The Madbi Formation,therefore, contains an effective source rock that has the greatest source po-tential within the Syun-Masila Basin based on thermal maturity, TOC content,thickness,and widespread distribution.

4.Materials and methods

The present study evaluates a detailed geochemical investiga-tion of twenty six crude oils represented different petroleum res-ervoirs and four selected samples from source rock of Upper Jurassic Madbi Formation(Tables1e3).The geochemical data on the crude oils and the source rock were interpreted in order to classify the oils genetic families and oil-source rock correlation.The oil-source rock correlation is essential to de?ne the petroleum system present in the Masila Region.Sample preparation and an-alyses were performed at Egyptian petroleum research institute (EPRI)-Cairo,Egypt.Details on analytical methods and compound identi?cations are described in Peters and Moldowan(1993).

Asphaltenes were precipitated from the crude oils by adding a 40fold excess of n-hexane.The precipitated asphaltenes were ?ltered.The hexane soluble material was separated by liquid chromatography into saturated hydrocarbons,aromatic hydrocar-bons and resins on an alumina and silica(both activated for2h at 200 C).The saturate and aromatic fractions were subjected to GC-FID and GC e MS analyses for biomarkers.A standard oil sample was analysed to ensure quality control and as a reference index for compound identi?cation and for absolute quanti?cation of steranes (Seifert and Moldowan,1979).

After initial screening by Rock-Eval Pyrolysis and total organic carbon determination,four organic-rich samples were selected for further detailed studies.The rock samples were selected from organic-rich shale intervals within the Madbi Formation(Fig.2). Rock samples were crushed to a?ne powder and then extracted with an azeotropic mixture of dichloromethane and methanol (93:7v/v).The total organic extracts were fractionated using open-column liquid chromatography to separate saturates,aromatics and polar compounds.Further GC-FID,GC e MS analyses were used as for the oil samples.For the analysis of biomarkers,the fragmento-grams for steranes(m/z217)and triterpanes(m/z191)were recorded.Individual components were identi?ed by comparison of their retention times and mass spectra with published data(Philp, 1985;Peters and Moldowan,1993;Hakimi et al.,2011b;Hakimi et al.,2012b).Relative abundances of triterpanes and steranes were calculated by measuring peak heights in the m/z191and m/z 217fragmentograms,respectively.

5.Results and discussion

Geochemical characteristics were used to identify groups of genetically related oils,to correlate oils with source rocks and to describe the probable source rock organic facies and depositional environment conditions.Based on these geochemical characteris-tics,the investigated oils were classi?ed into one genetic oil family. The source rock of this oil family contains a mixture of aquatic(algal and bacterial)and terrigenous organic matter that were deposited in a marine environment and were preserved under suboxic con-ditions.The depositional environment and organic facies were examined based on normal alkanes,isoprenoids,sterane,and tri-terpane distributions(Fig.3).The geochemical parameters or ratios used are pristane/phytane,pristane/n-C17,phytane/n-C18,waxiness index,homohopane index,C27/C29regular sterane,C27,C28,C29 regular steranes,dibenzothiophene/phenanthrene,presence or absence of tricyclic terpanes(Tables1and2).A number of cross plots or triangular plots using these ratios have also been con-structed(Figs.4e9).A description of the geochemical characteris-tics of the oil family follows.

5.1.Bulk properties of crude oils

The bulk crude oil properties and compositions for the studied oils are presented in Table1.The crude oils from Sunah oil?eld have API gravity values in the range of24.4e35.6 (Table1).The crude oils have high saturated and aromatic fractions and ranging from 40.0%to65.9%and28.0%e46.5%,respectively(Table1).The high saturated and aromatic fractions with low amount of asphaltene and resin components(Table1)indicating that these oils are naphthenic oils and no sign of biodegradation.The similar of bulk property and composition of the analysed crude oils indicates that only one oil type is present.

N.M.Al-Areeq,A.F.Maky/Marine and Petroleum Geology63(2015)17e27 20

Biodegradation process may occur in an oil reservoir,and the process dramatically affects the?uid properties of the hydrocar-bons(e.g.,Miiller et al.,1987).The early stages of oil biodegradation are characterized by the loss of n-alkanes or normal alkanes fol-lowed by loss of acyclic isoprenoids(e.g.,pristane and phytane). Compared with those compound groups,other compound classes (e.g.,highly branched and cyclic saturated hydrocarbons as well as aromatic compounds)are more resistant to biodegradation(Larter et al.,2005).In this respect,there is no sign of biodegradation among the studied oil samples,where the analysed oils contain a complete suite of n-alkanes in the low-molecular weight region and acyclic isoprenoids(e.g.,pristane and phytane;Fig.3).This is also indicated by the analysed oil samples generally contain more saturated hydrocarbons than aromatic hydrocarbons with gener-ally saturate/aromatic ratios>1(Table1).

The degree of waxiness is used to categorize the amount of land derived organic material in oil,assuming that terrigenous material contributes a high molecular weight normal paraf?n component to the oil(Hedberg,1968;Connan and Cassou,1980;Johns,1986). Recent studies about oil classi?cation by source input have relied heavily on waxiness as an environmental source input parameter (Connan and Cassou,1980).The degree of waxiness in this study is expressed by the S(n-C21e n-C31)/S(n-C15e n-C20)(Table1).The calculated ratio of waxiness degree ranges from0.53to 1.27 (Table1),suggesting that these oils have been derived from algal and/or bacterial and lower terrigenous organic matter contribution (Brooks et al.,1969;Tissot and Welte,1984).

5.2.Biomarker characteristics as indication for organic matter

input and depositional conditions

5.2.1.n-alkanes and isoprenoids

The gas chromatograms of saturated hydrocarbon fractions from representative two oil samples are shown in Figure3and derived parameters are listed in Table1.The saturated gas chromatograms of the oil samples display a full suite of saturated hydrocarbons between C10e C36n-alkanes and isoprenoids pristane(Pr)and phytane(Ph)(Fig.3).The similarity in the distribution patterns of n-alkanes with most abundant constituents(extending to C35)sug-gests that the studied oils are derived from one source and that no biodegradation has been occurred.The n-alkane distribution of the oils also show a predominance of low to medium molecular weight compounds(n-C10e n-C20)with the presence of signi?cant waxy alkanes(tn-C25),suggesting a signi?cant high contribution of marine organic matter with minor terrigenous organic matter contribution(Brooks et al.,1969;Powell and McKirdy,1973;Tissot et al.,1978;Ebukanson and Kinghorn,1986;Murray and Boreham, 1992).

Acyclic isoprenoids occur in a signi?cant amount in all studied oil samples(Fig.3)and diagnostic biomarker ratios are listed in Table1.The pristane/phytane(Pr/Ph)ratio is one of the most commonly used geochemical parameters and has been widely invoked as an indicator of the redox conditions in the depositional environment and source of organic matter(Didyk et al.,1978; Powell,1988;Chandra et al.,1994;Large and Gize,1996).High Pr/ Ph(>3.0)indicates oxic conditions often associated with terrige-nous organic matter input,while low values(<1.0)typify anoxic conditions,commonly hypersaline or carbonate environments (Peters et al.,1995,2005)and values between1.0and3.0suggest intermediate conditions(suboxic conditions)(Philp,1985;Amane and Hideki,1997).In the present study,pristane,occur in high relative concentrations,possessing pristane/phytane(Pr/Ph)ratios in the range of1.55e2.05suggest that the studied oils considered to be derived from source rock contain mixed organic facies and suboxic depositional conditions(Peters and Moldowan,1993; Hakimi et al.,2012b).Furthermore,lower amounts of acyclic iso-prenoids compared to n-alkanes(Fig.3),thus giving distinctively low pristane/n-C17and phytane/n-C18ratios in the range of

Table1

Bulk organic geochemical of crude oil samples from Sunah oil?eld,Masila Region.

Crude oils Depths(m)Reservoir rocks API gravity(o)Hydrocarbons Non-hydrocarbons Saturate/

aromatic Waxiness

degree

n-alkane and isoprenoids

Saturate Aromatic Asphaltenes Resins Pr/Ph Pr/n-C17Ph/n-C18CPI

CO-12088S1A Unit27.947.439.68.2 4.8 1.20.82 1.810.620.400.99 CO-22225S1A Unit29.350.437.37.4 4.9 1.40.94 1.850.570.360.98 CO-32195S1A Unit24.743.243.97.9 5.0 1.00.53 1.770.760.480.97 CO-412140S2Unit24.74146.5 6.4 6.10.90.68 1.760.640.420.99 CO-422165S2Unit24.642.744.57.3 5.5 1.00.63 1.800.670.430.96 CO-432183S2Unit24.444.740.49.0 5.9 1.10.68 1.790.650.420.98 CO-442206S2Unit25.847.142.6 5.3 5.0 1.10.64 1.710.770.520.97 CO-452240S3Unit26.547.440.67.4 4.6 1.20.69 1.760.720.460.98 CO-462258S3Unit29.949.736.610.3 3.4 1.4 1.03 1.780.560.370.99 CO-472285S3Unit29.949.537.010.8 2.7 1.30.79 1.900.620.40 1.00 CO-512157S2Unit31.853.237.0 6.7 3.1 1.4 1.01 1.850.570.370.98 CO-522188S2Unit32.353.137.37.4 2.2 1.4 1.06 1.810.560.370.98 CO-532208S2Unit31.957.734.7 5.3 2.3 1.7 1.05 1.770.550.370.98 CO-542230S2Unit27.746.039.010.1 4.9 1.20.92 1.700.610.420.98 CO-552258S3Unit30.152.437.17.1 3.4 1.40.99 1.820.570.370.99 CO-612207S2Unit30.351.637.18.2 3.1 1.40.83 1.780.590.390.99 CO-622218S2Unit31.451.738.3 6.3 3.7 1.30.99 1.760.570.390.98 CO-6322340S2Unit28.840.043.99.07.10.9 1.03 1.640.510.370.99 CO-642265S3Unit28.446.038.810.1 5.1 1.2 1.04 1.610.510.38 1.00 CO-712119S1A Unit28.143.637.514.6 4.3 1.2104 1.580.520.380.98 CO-722173S2Unit N.D.47.041.87.0 4.2 1.1 1.01 1.620.510.370.98 CO-732193S2Unit33.756.337.8 4.6 1.3 1.5 1.27 1.670.420.300.99 CO-812045S1A Unit33.560.232.4 3.4 4.0 1.9 1.09 1.990.480.270.98 CO-822105S2Unit33.865.928.0 3.6 2.5 2.4 1.12 2.050.480.270.96 CO-832112S2Unit33.853.333.5 4.88.4 1.6 1.03 1.680.460.310.98 CO-842195S2Unit35.650.731.515.3 2.5 1.6 1.21 1.550.410.310.97

Pr:pristane.

Ph:phytane.

CPI:carbon preference index(2[C23tC25tC27tC29]/[C22t2{C24tC26tC28}tC30]).

Waxiness degree:S(n-C21e n-C31)/S(n-C15e n-C20).

N.M.Al-Areeq,A.F.Maky/Marine and Petroleum Geology63(2015)17e2721

0.41e 0.77and 0.27e 0.52,respectively,corresponding to mixed organic matter deposited under suboxic conditions (Fig.4).This is supported by Pr/Ph vs.degree of waxiness,indicate one oil type generated from mixed marine organic matter deposited in suboxic conditions (Fig.5).

5.2.2.Triterpanes and steranes

The distributions of steranes and triterpanes are commonly studied using GC e MS by monitoring the ions m/z 217and m/z 191,respectively (Brooks et al.,1969;Peters et al.,2005).The distribu-tions of triterpanes and steroidal saturate biomarkers are very similar in the studied oils (Fig.3).The assignment of the peaks of steranes and triterpanes labelled in Figure 3are listed in Appendix 1.The similarity in the distribution patterns of m/z 191and m/z 217mass fragmentograms suggest that the studied oils are classi ?ed into one oil family (Fig.3).

The m/z 191mass fragmentograms of the saturated hydrocar-bon fractions of all the oil samples analysed display high pro-portions of hopanes relative to tricyclic terpanes as shown in Figure 3.The relative abundance of C 29norhopane is generally half or less than that of C 30hopane in most of the studied oil samples (Fig.3),with C 29/C 3017a (H)hopane ratios in the range of 0.36e 0.47(Table 2),indicating that these oil generated from clay-rich source rock (Gürgey,1999).The oils possess Ts/Tm ratio in the range of 1.09e 1.92(Table 2).However,Values of Tm (C 2717a (H)-22,29,30-trisnorhopane)and Ts (C 2718a (H)-22,29,30-trisnorneohopane)are well known to be in ?uenced by maturation,type of organic matter,and lithology (Moldowan et.al.,1985).The studied oil samples contain a mixture of land and marine derived organic matter;thus,the variation of Ts/Tm ratios appear to be more strongly in ?uenced by maturity instead of source input.Extended hopanes are dominated by the C 31homohopane and generally decreasing towards the C 35homohopane (Fig.3).The distribution of the extended hopanes or homohopanes (C 31e C 35)has been used to evaluate redox conditions based on homohopanes index (Peters et al.,2005).This,in turn,suggests that the studied oils were derived from source rock deposited under suboxic conditions.In support,relatively lower homohopanes index were obtained for the studied oils in the range of 0.08e 0.13(Table 2).Typically,such a distribution of homohopanes also commonly represents clastic facies (Waples and Machihara,1991)or a clay-rich character (Obermajer et al.,1999)as indicated by the predominance of C 30hopane in the m/z 191mass fragmentograms (Fig.3).Tricyclic terpane concentrations are also present in signi ?cant quantities (Fig.3).The tricyclic terpane concentrations detected in the studied oils supports contribution from marine-derived organic matter to the source rocks (Aquino Neto et al.,1983;Philp,1985;Waples and Machihara,1991).

The distributions of diasterane and the sterane (C 27,C 28and C 29)are characterized by the m/z 217ion chromatograms (Fig.3).Relative abundances of C 27,C 28and C 29regular steranes are calcu-lated and the results are given in Table 2.The distributions of C 27/

Table 2

Biomarker parameters of the crude oil samples dependent on source organic matter,depositional conditions and thermal maturity.Crude oils Saturated biomarker distributions

Aromatic biomarker distributions Triterpanes and terpanes (m/z191)

Steranes (m/z217)

Phen

Steroids Phenanthrene VRc (%)VRm

(%)

C 3222S/(22S t22R)

C 29/C 30Ts/Tm MC 30/HC 30C 29TS/C 29H Index C 2920S/(20S t20R)C 29bb /

(bb taa )C 27/C 29regular steranes

Regular steranes (%)DBT Phen MDR MPI

C 27C 28C 29

CO-1

0.570.41 1.170.120.530.100.540.540.8836.921.441.7

0.24 1.680.510.710.63CO-20.580.40 1.250.150.620.100.550.540.8735.922.841.30.23 1.610.590.750.63CO-30.570.42 1.330.130.570.100.550.530.8435.522.042.50.28 1.610.620.770.63CO-410.580.42 1.090.130.540.100.520.530.8536.221.442.40.28 1.810.620.770.64CO-420.580.42 1.180.120.560.100.510.540.8736.222.141.60.29 1.600.620.770.63CO-430.570.41 1.140.110.610.100.520.540.8235.122.142.80.27 1.530.620.770.62CO-440.570.42 1.260.130.560.100.510.550.8836.322.641.10.26 1.510.600.760.62CO-450.570.41 1.120.130.600.100.550.550.8536.121.642.30.25 1.610.610.770.63CO-460.570.40 1.310.090.610.090.540.560.8335.621642.70.22 1.580.560.740.63CO-470.560.41 1.390.100.600.090580.560.8335.521.742.80.23 1.590.560.740.63CO-510.570.39 1.410.100.630.090530.560.8636.022.042.00.22 1.560.540.720.62CO-520.570.41 1.370.100.590.080.54056

0.8135.620.444.00.22 1.520.550.730.62CO-530.570.40 1.250.100.620.080550.570.8435.921.642.50.40 1.520.540.720.62CO-540.570.45 1.240.090.520.090

540.510.8535.722.441.90.46 1.420.570.740.61CO-550.570.42 1.570.100.60.090.550.530.8435.222.841.90.40 1.510.560.740.62CO-610.580.42 1.340.090.580.080.530.530.9336.424.639.00.45 1.430.550.730.61CO-620.570.41 1.680.100.610.090.520.510.8435.422.342.30.44 1.480.540.720.62CO-630.570.46 1.310.070.520.090.510.520.8034.222.942.90.69 1.410.50.700.61CO-640.570.47 1.230.060.530.090.510.510.8235.421.243.40.74 1.470.510.710.62CO-710.570.46 1.340.060.510.090.510.520.8636.121.742.20.76 1.460.500.700.62CO-720.570.46 1.420.060.540.090.520.520.8334.923.241.90.74 1.480.510.710.62CO-730.560.46 1.560.110.640.090.530.560.9036.823.340.8 1.04 1.960.520.710.65CO-810.570.36 1.920.220.790.100.560.550.9236.723.340.00.26 2.060.580.750.66CO-820.570.37 1.650.230.800.100.510.540.9341.613.944.60.25 2.250.570.740.67CO-830.580.63 1.120.080.400.130.500.540.8134.622.642.90.57 1.610.570.740.63CO-84

0.58

0.46

1.17

0.09

0.58

0.10

0.52

0.57

0.83

35.821.0

43.2

0.67 2.110.520.710.66

Ts:(C 2718a (H)-22,29,30-trisnorneohopane).Tm:(C 2717a (H)-22,29,30-trisnorhopane).C 29/C 30:C 29norhopane/C 30hopane.

MC 30/HC 30:C 30moretane/C 30hopane H Index:(C 35/(C 31e C 35)homohopane.DBT/Phen:dibenzothiophene/phenanthrene.MDR:MDR,4-MDBT/1-MDBT.MPI:Methylphenanthrene Index.VRc (%):0.60*MPI t0.40.VRm (%):0.073*MDR t0.51.

N.M.Al-Areeq,A.F.Maky /Marine and Petroleum Geology 63(2015)17e 27

22

C 28/C 29regular steranes for all oil samples are very similar (C 29>C 27>C 28)as are the ratios of C 27/C 29regular steranes and the thermal maturity indicators C 2920S/(20S t20R)and bb /(bb taa )(Table 2).The relative distribution of C 27e C 29regular steranes is used to indicate source of organic matter input (Huang and Meinschein,1979;Waples and Machihara,1991).Based on this classi ?cation,the studied oil samples derived from similar types of organic matter (Fig.6).The oil samples display a composed of C 27e C 29steranes which is an indicator of the mixed marine/terrigenous organic matter (Fig.6)as indicated by Pr/n -C 17and Ph/n -C 18ratios (Fig.4).This is also suggested by values of C 27/C 29regular steranes ratio (Fig.7)and the presence of tricyclic terpane in the m/z 191mass fragmentograms (Fig.3).

5.2.3.Dibenzothiophenes

The two molecular indicators,the ratio of dibenzothiophene/phenanthrene and the ratio of pristane/phytane,can be also used to infer crude oil source rock depositional environments and lithol-ogies (Hughes et al.,1995).The dibenzothiophene/phenanthrene ratio of Sunah oils ranges from 0.22to 1.04(Table 2)such a range indicates that these oils have been derived from paralic/clastic source input (Sivan et al.,2008).Furthermore,the ratio of diben-zothiophene/phenanthrene is plotted against pristane/phytane ratio,the values fall in a typical pattern.The cross plot of diben-zothiophene/phenanthrene versus pristane/phytane indicates that Sunah oils are derived from marine shales (Fig.8).5.3.Thermal maturity of crude oils

In this study,a variety of biomarker maturity indicators have been used to evaluate the level of thermal maturity of the Sunah oils;these include pentacyclic triterpanes and sterane isomer ra-tios,methyl phenanthrene index (MPI)and methyl dibenzothio-phene ratio (MDR)(Table 2).In gas chromatography e mass spectrometry (GC e MS),biomarker maturation parameters such as C 3222S/(22S t22R)homohopane,moretane/hopane and 20S/(20S t20R)and bb /(bb taa )C 29sterane ratios,were used as maturity indicators (Mackenzie et al.,1980;Waples and Machihara,1991;Peters and Moldowan,1993;Peters et al.,2005).The ratios of 22S/(22R t22S)for C 3217a (H),21b (H)-hopanes and 20S/(20S t20R)and bb /(bb taa )C 29sterane are ranging from 0.56to 0.58,0.50to 0.56and 0.51to 0.57,respectively (Table 2)suggesting that they have reached equilibrium (Seifert and Moldowan,1986)and that the oil window has been reached.Furthermore,the maturity ratios of bb /(bb taa )and 20S/(20S t20R)for C 29sterane are plotted against ratio.This correlation re ?ects that the oils are early mature to peak oil window (Fig.9).The relationship between isoprenoids Pr/n -C 17and Ph/n -C 18ratios (Fig.4)re ?ects the same interpretation as do the moretane/hopane ratios consistent with low relative abundance of C 30moretane (Waples and Machihara,1991).Moretane converts to C 30hopane with increasing thermal maturity (Seifert and Moldowan,1986),and thus,moretane de-creases as thermal maturity increases.The ratio of moretane to their corresponding hopanes decreases with increasing thermal maturity,from about 0.8in immature sediments to about 0.15e 0.05in mature source rocks and oils (Mackenzie et al.,1980;Seifert and Moldowan,1986).The studied oils have moretane/hopane ratio in the range of 0.07e 0.23,suggests the oils samples generated from early to peak mature source rock.

The methyl phenanthrene index (MPI)and methyl dibenzo-thiophene ratio (MDR)were also used as thermal maturity in-dicators.The methyl phenanthrene index (MPI)(Radke and Welte,1983)yields calculated vitrinite re ?ectance (VRc %),whereas the maturity parameter equivalent to vitrinite re ?ectance (VRm %)calculated based on methyl dibenzothiophene ratio (Table 2).The

T a b l e 3S u m m a r y o f t y p i c a l g e o c h e m i c a l p a r a m e t e r d i s t r i b u t i o n s f o r S u n a h c r u d e o i l s a n d p o t e n t i a l M a d b i s o u r c e r o c k e x t r a c t s .

S a m p l e s

R e s e r v o i r /s o u r c e r o c k a g e

n -a l k a n e a n d i s o p r e n o i d s

T r i t e r p a n e s a n d t e r p a n e s (m /z 191)

S t e r a n e s a n d d i a s t e r a n e s (m /z 217)

P r /P h

P r /C 17P h /C 18

C P I

W a x i n e s s d e g r e e

C 3222S /(22S t22R )C 29/C 30

M C 30/H C 30

H I n d e x

C 2920S /(20S t20R )

C 29b b /(b b ta a )

C 27/C 29

r e g u l a r s t e r a n e s

R e g u l a r s t e r a n e s (%)

C 27

C 28

C 29

S u n a h o i l s

L o w e r C r e t a c e o u s 1.55e 2.050.41e 0.770.27e 0.52

0.96e 1.00

0.53e 1.27

0.56e 0.580.36e 0.630.06e 0.23

0.08e 0.130.50e 0.580.51e 0.570.80e 0.93

34.2e 41.613.9e 24.639.0e 44.6M a d b i S h a l e s U p p e r J u r a s s i c

1.990.980.621.001.010.590.370.150.090.540.510.9338.021.240.8

2.020.920.570.991.030.580.400.130.090.520.521.0240.020.639.31.990.900.621.011.030.590.420.150.080.530.500.9839.719.640.71.821.050.751.041.06

0.58

0.39

0.140.080.510.501.0943.6

16.3

40.1

P r :p r i s t a n e .P h :p h y t a n e .C P I :c a r b o n p r e f e r e n c e i n d e x (2[C 23tC 25tC 27tC 29]/[C 22t2{C 24tC 26tC 28}tC 30]).W a x i n e s s d e g r e e :S (n -C 21e n -C 31)/S (n -C 15e n -C 20).C 29/C 30:C 29n o r h o p a n e /C 30h o p a n e .M C 30/H C 30:C 30m o r e t a n e /C 30h o p a n e .H I n d e x :(C 35/(C 31àC 35)h o m o h o p a n e .

N.M.Al-Areeq,A.F.Maky /Marine and Petroleum Geology 63(2015)17e 2723

Sunah oils have vitrinite re ?ectances VRc %and VRm %values in the

range of 0.70e 0.77and 0.61e 0.66,respectively,indicating that the

oils are thermally mature.

5.4.Inferred oil-source correlation

The Upper Jurassic marine Madbi Formation is a recognized

source rock in the Syun-Masila Basin and has generated oil that has

been found in lower Cretaceous and Jurassic as well as fractured basements reservoirs.The objective of this part in this study is to investigate the genetic link between the oils recovered from Sunah oil ?eld in the Masila Region and Upper Jurassic Madbi Formation.In an attempt to develop an oil-source rock correlation,we extracted soluble bitumens from four samples of the Madbi shale and analysed their biomarkers using GC and GC e MS analyses.Overall,the oil data closely match the Upper Jurassic source rock data.Key factors include biomarker parameters (Table 3)and the similar positions on the cross-plots (Figs.4e 9

).Figure 3.Gas chromatography traces and m/z 191,m/z 217mass fragmentograms for representative two oil

samples.

Figure 4.Phytane to n -C 18alkane (Ph/n -C 18)versus pristane to n -C 17alkane (Pr/n -C 17)

ratios for Sunah crude oils and source rock

extracts.Figure 5.Relationship between isoprenoid ratios and degree of waxiness S (n -C 21e n -C 31)/S (n -C 15e n -C 20)for investigated crude oils from Sunah oil ?eld and source rock

extracts in the Masila Region.N.M.Al-Areeq,A.F.Maky /Marine and Petroleum Geology 63(2015)17e 27

24

Extract from the Madbi shale has nearly equal quantity of tC 25n-alkane waxy component to the oil samples (Table 3).Pristane/phytane and Pr/n-C 17vs.Ph/n-C 18ratios suggest a mixed organic matter input deposited under suboxic conditions and relatively mature source rock extract (Fig.4).The Carbon Preference Index (CPI)value is in the range of 0.99e 1.04,which also indicates a mixed input of terrestrial and marine organic matter and slightly mature samples (Bray and Evans,1961).

In the terpane distributions of the Madbi shale extract,presence tricyclic terpanes,low C 29-norhopane/C 30-hopane ratios and rela-tively low homohopanes index (Table 3),suggest clay-rich marine source rock and suboxic conditions prevailed during the deposition as suggested by dibenzothiophene/phenanthrene ratios (Fig.8).The steranes distribution shows composed of C 27e C 29regular steranes and relatively low C 27/C 29regular steranes ratios (Figs.6and 7;Table 3),suggest a combination of marine and terrestrial organic matter input (Moldowan et al.,1985;Peters and Moldowan,1993).

On a plot of ratios 22S/(22S t22R)and bb /(bb taa )for C 29steranes,the Madbi Formation is considered thermally mature and the oil window has been reached (Fig.9).Therefore the Upper Jurassic Madbi source for the crude oil can be suggested.The C 30moretane/C 30hopane ratios are also consistent with the level of thermal maturity (Table 3).6.Conclusions

Geochemical characterization based upon biomarker compo-nents coupled with the bulk geochemical parameters were used to arrive at a clear characterization and classi ?cation of the Sunah crude oils in the Masila Region.The ?ngerprints have been achieved from the acyclic isoprenoids,triterpane and sterane biomarkers.One oil family is observed and represented in the suite of Sunah oil samples according to their source.The investigated biomarkers of Sunah oils are characterized by a dominance of low to medium molecular weight n -alkane compounds with the presence of waxy alkanes (tn-C 25),moderately high Pr/Ph ratio (1.55e 2.05),rela-tively low C 35homohopane index,composed of C 27e C 29regular steranes,relatively low C 27/C 29regular steranes,and the

presence

Figure 6.Ternary diagram of regular steranes (C 27e C 29)showing the relationship between sterane compositions,source organic matter input (modi ?ed after Huang and Meinschein,1979

).

Figure 7.A plot of pristane/phytane versus C 27/C 29regular steranes,indicating organic matter input and depositional

conditions.

Figure 8.Cross plot of dibenzothiophene/phenanthrene (DBT/Phe)versus pristane/phytane (Pr/Ph)ratios provides a novel,convenient and powerful way to infer crude oil source rock depositional environments and lithologies (Hughes et al.,1995

).

Figure 9.A range of thermal maturity based on two maturity related biomarker pa-rameters [C 2922S/(22S t22R)and C 29bb /(bb taa )]for the studied oil samples and source rock extracts.

N.M.Al-Areeq,A.F.Maky /Marine and Petroleum Geology 63(2015)17e 2725

of tricyclic terpanes as well as relatively low dibenzothiophene/phenanthrene ratios.These data indicate that the oils were gener-ated from source rock contain a mixture of aquatic (algal and bacterial)and terrigenous organic matter that were deposited in a suboxic marine conditions.Maturity estimates based on biomarker maturity parameters indicate that all oils had reached and/or sur-passed the peak of the oil window.Previous studies suggested that the Upper Jurassic Madbi Formation is the major source for the oil in the Masila Region.Only four organic-rich samples of the Madbi Formation were available in this study.The geochemical charac-teristics obtained from the solvent extracts of these samples are generally similar and seems the best candidate to those oils.The similarity of the geochemical characteristics further corroborates the possibility suggested that the Madbi Formation is the best source rock for the oil in the Sunah oil ?eld in the Masila Region.Acknowledgements

The authors thank the Petroleum Exploration and Production Authority (PEPA),Yemen for supplying the data and samples for this study.Appendix 1

References

Al-Areeq,N.,2008.Sedimentological Evolution and Petroleum System in the Cen-tral Part of Sayun-masila Basin,Republic of Yemen (PhD thesis).Faculty of Science-Assiut University,341pp .

Al-Areeq,N.M.,Abu El Ata,A.S.,Maky,A.F.,Omran,A.A.,2011.Hydrocarbon Po-tentialities of some upper Jurassic Rock units in Masila block,Sayun-Masila Basin,Yemen.National research Center,Cairo.J.Appl.Geophys.10(2),147e 168.Amane,W.,Hideki,N.,1997.Geochemical characteristics of terrigenous and marine

sourced oils in Hokkaido,befca13281c758f5f71f6704.Geochem.28,27e 41.

Aquino Neto,F.R.,Trendel,J.M.,Restle,A.,Connan,J.,Albrecht,P.A.,1983.Occurrence

and formation of tricyclic and tetracyclic terpanes in sediments and petro-leums.In:Bjor?y,M.,et al.(Eds.),Advances in Organic Geochemistry,1981.John Wiley and Sons,pp.659e 667.

Beydoun,Z.R.,Al-Saruri,M.,El-Nakhal,H.,Al-Ganad,I.N.,Baraba,R.S.,Nani,A.S.O.,

Al-Aawah,M.H.,1998.International Lexicon of Stratigraphy In:International Union of Geological Sciences and Ministry of Oil and Mineral Resources,second ed.,vol.III.Republic of Yemen Publication 34,Republic of Yemen,p.245.

Bray,E.E.,Evans,E.D.,1961.Distribution of n-paraf ?ns as a clue to recognition of

source beds.Geochim.Cosmochim.Acta 22,2e15.

Brooks,J.D.,Gould,K.,Smith,J.W.,1969.Isoprenoid hydrocarbons in coal and pe-troleum.Nature 222,257e 259.

Chandra,K.,Mishra,C.S.,Samanta,U.,Gupta,A.,Mehrotra,K.L.,1994.Correlation of

different maturity parameters in the Ahmedabad e Mehsana block of the Cam-bay befca13281c758f5f71f6704.Geochem.21,313e 321.

Connan,J.,Cassou,A.M.,1980.Properties of gases and petroleum liquids derived

from terrestrial kerogen at various maturation levels.Geochim.Cosmochim.Acta 44,1e 23.

Didyk,B.M.,Simoneit,B.R.T.,Brassell,S.C.,Eglinton,G.,befca13281c758f5f71f6704anic geochemical

indicators of palaeoenvironmental conditions of sedimentation.Nature 272,216e 222.

Ebukanson,E.J.,Kinghorn,R.R.F.,1986.Maturity of organic matter in the Jurassic of

southern England and its relation to the burial history of the sediments.J.Pet.Geol.93,259e 280.

Gürgey,K.,1999.Geochemical characteristics and thermal maturity of oils from the

Thrace Basin (western Turkey)and western Turkmenistan.J.Pet.Geol.22,167e 189.

Hakimi,M.H.,Abdullah,W.H.,Shalaby,M.R.,2012a.Geochemical and petrographic

characterization of organic matter in the Upper Jurassic Madbi shale succession (Masila Basin,Yemen):origin,type and befca13281c758f5f71f6704.Geochem.49,18e 29.Hakimi,M.H.,Abdullah,W.H.,Shalaby,M.R.,2012b.Molecular composition and

organic petrographic characterization of Madbi source rocks from the Kharir oil ?eld of the Masila Basin (Yemen):palaeoenvironmental and maturity inter-pretation.Arab.J.Geosci.5,817e 831.

Hakimi,M.H.,Abdullah,W.H.,Shalaby,M.R.,befca13281c758f5f71f6704anic geochemical charac-teristics and depositional environments of the Jurassic shales in the Masila Basin of Eastern Yemen.GeoArabia 16(1),47e 64.

Hakimi,M.H.,Abdullah,W.H.,Shalaby,M.R.,befca13281c758f5f71f6704anic geochemical charac-teristics of crude oils from the Masila Basin,eastern befca13281c758f5f71f6704.Geochem 42,465e 476.

Hakimi,M.H.,Abdullah,W.H.,Shalaby,M.R.,2010.Source rock characterization and

oil generating potential of the Jurassic Madbi Formation,onshore East Shabo-wah oil ?elds,Republic of befca13281c758f5f71f6704.Geochem.41,513e 521.

Hedberg,H.D.,1968.Signi ?cance of high-wax oil with respect to genesis of petro-leum.Am.Assoc.Pet.Geol.Bull.52,736e 750.

Huang,W.Y.,Meinschein,W.G.,1979.Sterols as ecological indicators.Geochim.

Cosmochim.Acta 43,739e 745.

Hughes,W.B.,Holba,A.G.,Dzou,L.I.P.,1995.The ratios of dibenzothiophene to

phenanthrene and pristane to phytane as indicators of depositional environ-ment and lithology of petroleum source rocks.Geochim.Cosmochim.Acta 59,3581e 3598.

Johns,R.B.,1986.Biological Markers in the Sedimentary Record.Elsevier,

Amsterdam .

King,W.A.,Mills,B.R.,Gardiner,S.,Abdillah,A.A.,2003.The Masila ?elds,Republic

of Yemen.In:Halbouty,M.T.(Ed.),Giant Oil and Gas Fields of the Decade 1990e 1999,American Association of Petroleum Geologists Memoir,vol.78,pp.275e 295.

Large, D.J.,Gize, A.P.,1996.Pristane/phytane ratios in the mineralized Kupfer-schiefer of the Fore-Sudetic Monocline,southwest Poland.Ore Geol.Rev.11,89e 103.

Larter,S.R.,Head,I.M.,Huang,H.,Bennett,B.,Jones,M.,Aplin,A.C.,Murray,A.,

Erdmann,M.,Wilhelms,A.,di Primio,R.,2005.Biodegradation,Gas destruction and methane generation in deep subsurface petroleum reservoirs:an overview.In:Dore,A.G.,Vining,B.(Eds.),Petroleum Geology:Northwest Europe and Global Perspectives:Proceedings of the 6th Petroleum Geology Conference.Geological Society,London,pp.633e 640.

Mackenzie,A.S.,Patience,R.L.,Maxwell,J.R.,Vandenbroucke,M.,Durand,B.,1980.

Molecular parameters of maturation in the Toarcian shales,Paris Basin,France.Changes in the con ?guration of acyclic isoprenoids alkanes,steranes and tri-terpanes.Geochim.Cosmochim.Acta 44,1709e 1721.

Miiller,D.E.,Holba,A.G.,Huges,W.B.,1987.Effects of biodegradation on crude oils.

In:Meyer,R.F.(Ed.),Exploration for Heavy Crude Oil and Natural Bitumen.American Association of Petroleum Geologists Studies,pp.233e 241.

Mills,S.J.,1992.Oil discoveries in the Hadramaut:how Canadian oxy scored in

Yemen.Oil Gas J.49,52(9March).

Moldowan,J.M.,Seifert,W.K.,Gallegos,E.J.,1985.Relationship between petroleum

composition and depositional environment of petroleum source rocks.Am.Assoc.Pet.Geol.Bull.69,1255e 1268.

Murray,A.P.,Boreham,C.J.,befca13281c758f5f71f6704anic Geochemistry in Petroleum Exploration.

Australian Geological Survey Organization,Canberra,p.230.

Obermajer,M.,Fowler,M.G.,Snowdon,L.R.,1999.Depositional environment and oil

generation in Ordovician source rocks from southwestern Ontario,Canada:organic geochemical and petrological approach.Am.Assoc.Pet.Geol.Bull.83,1426e 1453.

Peters,K.E.,Walters,C.C.,Moldowan,J.M.,2005.The Biomarker Guide.Cambridge

University Press,UK,p.1155.

Peters,K.E.,Clark,M.E.,Das Gupta,U.,McCaffrey,M.A.,Lee,C.Y.,1995.Recognition of

an Infracambrian source rock based on biomarkers in the Baghewala-1oil,In-dia.Am.Assoc.Pet.Geol.Bull.79,1481e 1494.

Peters,K.E.,Moldowan,J.M.,1993.The Biomarker Guide:Interpreting Molecular

Fossils,Petroleum and Ancient Sediments.Prentice Hall,New Jersey,p.363.Philp,R.P.,1985.Biological markers in fossil fuel production.Mass Spectrom.Rev.4,

1e 54.

Peak assignments for alkane hydrocarbons in the gas chromatograms of aliphatic fractions in the m /z 191(I)and 217(II)mass fragmentograms compound abbreviation (I)Peak no.Ts 18a (H),22,29,30-trisnorneohopane Ts Tm 17a (H),22,29,30-trisnorhopane Tm

2917a ,21b (H)-nor-hopane C29hop 3017a ,21b (H)-hopane Hopane 3M 17b ,21a (H)-Moretane

C 30Mor 31S 17a ,21b (H)-homohopane (22S)C 31(22S)31R 17a ,21b (H)-homohopane (22R)C 31(22R)32S 17a ,21b (H)-homohopane (22S)C 32(22S)32R 17a ,21b (H)-homohopane (22R)C 32(22R)33S 17a ,21b (H)-homohopane (22S)C 33(22S)33R 17a ,21b (H)-homohopane (22R)C 33(22R)34S 17a ,21b (H)-homohopane (22S)C 34(22S)34R 17a ,21b (H)-homohopane (22R)C 34(22R)35S 17a ,21b (H)-homohopane (22S)C 35(22S)35R

17a ,21b (H)-homohopane (22R)C 35(22R)(II)Peak no.a 13b ,17a (H)-diasteranes 20S Diasteranes b 13b ,17a (H)-diasteranes 20R Diasteranes c 13a ,17b (H)-diasteranes 20S Diasteranes d 13a ,17b (H)-diasteranes 20R Diasteranes e 5a ,14a (H),17a (H)-steranes 20S aaa 20S f 5a ,14b (H),17b (H)-steranes 20R abb 20R g 5a ,14b (H),17b (H)-steranes 20S abb 20S h

5a ,14a (H),17a (H)-steranes 20R

aaa 20R

N.M.Al-Areeq,A.F.Maky /Marine and Petroleum Geology 63(2015)17e 27

26

Powell,T.G.,1988.Pristane/phytane ratio as environmental indicator.Nature333, 604.

Powell,T.G.,McKirdy,D.M.,1973.Relationship between ratio of pristane to phytane, crude oil composition and geological environment in Australia.Nat.Phys.Sci.

243,37e39.

Redfern,P.,Jones,J.A.,1995.The interior basins of Yemen-analysis of basin structure and stratigraphy in a regional plate tectonic context.Basin Res.7,337e356. Radke,M.,Welte,D.H.,1983.The methylphenanthrene index(MPI):a maturity parameter based on aromatic hydrocarbons.In:Bjoroy,M.(Ed.),Advances in Organic Geochemistry1981.Wiley,Chichester,pp.504e512.

Seifert,W.K.,Moldowan,J.M.,1979.The effect of biodegradation on steranes and terpanes in crude oils.Geochim.Cosmochim.Acta43,111e126.

Seifert,W.K.,Moldowan,J.M.,befca13281c758f5f71f6704e of biological markers in petroleum explo-ration.In:Johns,R.B.(Ed.),Methods in Geochemistry and Geophysics24, pp.261e290.

Sivan,P.,Datta,G.C.,Singh,R.R.,2008.Aromatic biomarkers as indicators of source, depositional environment,maturity and secondary migration in the oils of Cambay Basin,befca13281c758f5f71f6704.Geochem.39,1620e1630.Smewing,J.D.,1997.A High Resolution Sequence Stratigraphic Study of the Shuqra Formation in the Aden e ahwar Area of Coastal South Yemen.Earth Resources Institute,Swansea,Wales unpublished proprietary consultant study to Nexen, 29pp.

Smewing,J.D.,Saeed,A.R.,Ahmed,A.M.,1998.A high resolution sequence strati-graphic study of the Callovian to Early Kimmeridgian Shuqra formation in the Aden e Ahwar area of coastal South Yemen.In:Geo'98Conference Program with Abstracts,Manama,Bahrain,April20e22,1998,GeoArabia3,p.154.

Tissot,B.P.,Welte,D.H.,1984.Petroleum Formation and Occurrence.Springer-Ver-lag,Berlin,p.699.

Tissot,B.P.,Deroo,G.,Hood,A.,1978.Geochemical study of the Uinta Basin:for-mation of petroleum from Green river formation.Geochim.Cosmochim.Acta 42,1469e1485.

Waples,D.W.,Machihara,T.,1991.Biomarkers for Geologists e a Practical Guide to the Application of Steranes and Triterpanes in Petroleum Geology.In:Associ-ation of Petroleum Geologists Methods in Exploration Series9,p.91.

N.M.Al-Areeq,A.F.Maky/Marine and Petroleum Geology63(2015)17e2727

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