API gravities,vanadium, nickel,sulfur, and their relation to gross composition: Implications for the origin and maturation of crude oils in Western Desert,Egypt

In the present study, the geochemical analyses of API gravities, vanadium, nickel, sulfur, and bulk composition were performed on eight samples from productive wells in Gindi, South Deep Abu-gharadig, Abu-gharadig, Dahab-Merier, and Faghure basins locates in the North Western Desert. The results were used to describe the source organic matter input, depositional environment, assess the degree of thermal maturity, and to correlate between crude oils to determine the genetic relationship between hydrocarbon generation and their source rock for the studied oil samples. The results showed that a wide range of crude oil parameters exists in this data, indicating that a variety of oil types is represented. Crude oils range from unaltered to altered by vanadium, nickel, and sulfur concentrations, V/Ni and saturate fraction were used to classify the oils. Oils are classified into two groups. Group I contains oil samples from Gindi, South deep Abu-gharadig and Abu-gharadig, and Dahab-Merier that are generated from organic matter input deposited in marine environment under anoxic to suboxic conditions. Group II from Faghur basin possess high Pr/Ph ratios suggesting high contribution of terreginous organic matter deposited under relatively oxic conditions.     

RELATIONSHIP BETWEEN PETROLEUM COMPOSITION AND DEPOSITIONAL ENVIRONMENT OF PETROLEUM SOURCE ROCKS FROM THE GULF OF SUEZ AND THE WESTERN DESERT OF EGYPT

Crude oils from the Gulf of Suez and the North Western Desert of Egypt have been analyzed for geochemical biomarkers using GC and GC-MS techniques. The biomarker compositions of the crude oils have been used to differentiate crude oils of non-marine, normal marine and marine carbonate sources. The geochemical features of Zaafarana crude oil from the Gulf of Suez Basin indicate a marine carbonate depositional setting. One crude oil from Budran however, possesses geochemical characteristics consistent with an origin from source rock deposited in normal marine conditions. Bahar and Morgan show normal marine source rock deposition environment with terrigenous organic matter input. On the other hand, the crude oils from the North Western Desert have bulk and biomarker characteristics cosistent with non-marine depositional setting, with the exception of one oil sample which appears to have a mixed marine/terrestrial sources. The presence of oleanane in some of these oils suggests source rocks deposited in deltaic or near shore environment in Post Cretaceous Basin.     

RELATIONSHIP BETWEEN PETROLEUM COMPOSITION AND DEPOSITIONAL ENVIRONMENT OF PETROLEUM SOURCE ROCKS FROM THE GULF OF SUEZ AND THE WESTERN DESERT OF EGYPT

ABSTRACT

Crude oils from the Gulf of Suez and the North Western Desert of Egypt have been analyzed for geochemical biomarkers using GC and GC-MS techniques. The biomarker compositions of the crude oils have been used to differentiate crude oils of non-marine, normal marine and marine carbonate sources. The geochemical features of Zaafarana crude oil from the Gulf of Suez Basin indicate a marine carbonate depositional setting. One crude oil from Budran however, possesses geochemical characteristics consistent with an origin from source rock deposited in normal marine conditions. Bahar and Morgan show normal marine source rock deposition environment with terrigenous organic matter input. On the other hand, the crude oils from the North Western Desert have bulk and biomarker characteristics cosistent with non-marine depositional setting, with the exception of one oil sample which appears to have a mixed marine/terrestrial sources. The presence of oleanane in some of these oils suggests source rocks deposited in deltaic or near shore environment in Post Cretaceous Basin.     

Characterization and correlation of crude oils from some wells in the North Western Desert,Egypt

Characterization and correlation of crude oils from some wells in the North Western Desert, based on six crude oil samples, were studied by different analytical techniques, including API gravity, sulfur content, nickel and vanadium, bulk compositions and saturated fraction obtained from gas chromatography have been studied. The results show that the crude oils are normal to medium aromatic oils, with high API gravity and high sulfur content. V, Ni, V/Ni and V/(V + Ni) reflecting oils might be sourced from non-clastic source rocks, possibly carbonates, deposited under anoxic-suboxic conditions. Bulk compositions revealing that the crude oils were derived from marine organic sources. While, the paraffins and naphthenes percent indicates that the oils belong to paraffinic to naphthenic oil types, deposited in slightly anoxic to suboxic conditions and contained marine organic matter. Thermal maturity data showed that the oil samples were generated from mature source rocks. This indicates the studied oil samples are well correlated with each other, where they are similar in their oil type maturation and source depositional environments.     

BIOMARKER GEOCHEMISTRY OF PALEOGENE CRUDE OILS AND SOURCE ROCKS FROM THE RAOYANG SAG,BOHAI BAY BASIN,NE CHINA: AN OIL – SOURCE ROCK CORRELATION STUDY

This study presents a systematic geochemical analysis of Paleogene crude oils and source rocks from the Raoyang Sag in the Jizhong sub-basin of the Bohai Bay Basin (NE China). The geochemical characteristics of fifty-three oil samples from wells in four sub-sags were analysed using gas chromatography (GC) and gas chromatography – mass spectrometry (GC-MS). Twenty core samples of mudstones from Members 1 and 3 of the Eocene-Oligocene Shahejie Formation were investigated for total organic carbon (TOC) content and by Rock-Eval pyrolysis and GC-MS to study their geochemistry and hydrocarbon generation potential. The oils were tentatively correlated to the source rocks. The results show that three groups of crude oils can be identified. Group I oils are characterized by high values of the gammacerane index and low values of the ratios of Pr/Ph, Ts/Tm, 20S/(20S+20R) C₂₉ steranes, ββ/(ββ+αα) C₂₉ steranes, C₂₇ diasteranes/ C₂₇ regular steranes and C₂₇/C₂₉ steranes. These oils have the lowest maturity and are interpreted to have originated from a source rock containing mixed organic matter deposited in an anoxic saline lacustrine environment. The biomarker parameter values of Group III oils are the opposite to those in Group I, and are interpreted to indicate a highly mature, terrigenous organic matter input into source rocks which were deposited in suboxic to anoxic freshwater lacustrine conditions. The parameter values of Group II oils are between those of the oils in Groups I and III, and are interpreted to indicate that the oils were generated from mixed organic matter in source rocks deposited in an anoxic brackish–saline or saline lacustrine environment. The results of the source rock analyses show that samples from Member 1 of the Shahejie Formation were deposited in an anoxic, brackish – saline or saline lacustrine environment with mixed organic matter input and are of low maturity. Source rocks in Member 3 of the Shahejie Formation were deposited in a suboxic to anoxic, brackish – saline or freshwater lacustrine environment with a terrigenous organic matter input and are of higher maturity. Correlation between rock samples and crude oils indicates that Group I oils were probably derived from Member 1 source rocks, while Group III oils were more likely generated by Member 3 source rocks. The Group II oils with transitional characteristics are likely to have a mixed source from both sets of source rocks.     

Distribution of triterpanes and steranes biomarkers as indication of organic matters input and depositional environments of crude oils of oilfields in Gulf of Suez,Egypt

Eight crude oils collected from different oilfields distributed within the northern, central and southern Gulf of Suez basin to detect the distribution of triterpanes and steranes biomarkers as indication of organic matter input and depositional environments of crude oils and lithology of organic matters. This achieved throughout the application of gas chromatography mass spectrometry analysis. The results revealed that the Gulf of Suez samples are believed to be of marine organic matter input deposited under anoxic depositional environment. Off shore samples S3 and S4 from Central Province of Gulf of Suez basin show low maturity levels, while the other samples which were of higher maturity levels.     

Oil Families and Their Potential Sources in the Southern Gulf of Suez,Egypt

Abstract

Four oil families are identified in the southern Gulf of Suez, through high-resolution geochemical studies including gas chromatography, gas chromatography–mass spectrometry, and carbon isotope analyses. Biological features characterize oils in family 1a, suggesting tertiary carbonate source rocks for these oils, rich in type II organic matter and deposited under anoxic depositional environment. Family 1b oil shows minor variations in the source of organic matter and the depositional environment, as it was derived from carbonate source rock with more algal and bacterial contribution and minor input of terrestrial organic sources, deposited under less saline condition compared to family 1a oil. Family 2 oil, although genetically related to family 1a oil, has some distinctive features, such as diasterane to sterane and pristane to phytane ratios, which suggest clay-rich source rocks and a more oxic depositional environment. Also, the lack of oleanane indicates pre-tertiary source rocks for this oil. In contrast, family 3 oil is of mixed sources (marine and non-marine), generated from low sulfur and clay-rich source rock of tertiary and/or younger age. Family 4 oil seems to be mixed from family 1b and family 3 oils, sourced mainly from carbonate source rocks rich in clay minerals with algal and bacterial contributions. Family 4 oil is highly mature, family 1b oil lies within equilibrium values (peak oil generation stage), while the other families are more or less near equilibrium.     

Oil Families and Their Potential Sources in the Southern Gulf of Suez, Egypt

Four oil families are identified in the southern Gulf of Suez, through high-resolution geochemical studies including gas chromatography, gas chromatography-mass spectrometry, and carbon isotope analyses. Biological features characterize oils in family 1a, suggesting tertiary carbonate source rocks for these oils, rich in type II organic matter and deposited under anoxic depositional environment. Family 1b oil shows minor variations in the source of organic matter and the depositional environment, as it was derived from carbonate source rock with more algal and bacterial contribution and minor input of terrestrial organic sources, deposited under less saline condition compared to family 1a oil. Family 2 oil, although genetically related to family 1a oil, has some distinctive features, such as diasterane to sterane and pristane to phytane ratios, which suggest clay-rich source rocks and a more oxic depositional environment. Also, the lack of oleanane indicates pre-tertiary source rocks for this oil. In contrast, family 3 oil is of mixed sources (marine and non-marine), generated from low sulfur and clay-rich source rock of tertiary and/or younger age. Family 4 oil seems to be mixed from family 1b and family 3 oils, sourced mainly from carbonate source rocks rich in clay minerals with algal and bacterial contributions. Family 4 oil is highly mature, family 1b oil lies within equilibrium values (peak oil generation stage), while the other families are more or less near equilibrium.     

BULK COMPOSITION OF SOME SAUDI ARABIAN CRUDE OILS IN RELATION TO MATURATION, ORIGIN AND DEPOSITIONAL ENVIRONMENTS

Ten crude oil samples, covering wide range of maturity (API = 18.5-36.1), were assembled from Safaniya, Abqiq, Ain-Dar, Wafra, Marjan, and Zulf oil fields in the area of Arabian Gulf. Different analytical techniques, including liquid chromatographic separation, gas chromatography, and nuclear magnetic resonance spectroscopy, were used to characterize the oil samples. Some bulk and specific compositional parameters were used for oil-oil correlations in order to evaluate thermal maturation, origin, biodegradation and depositional environments of the crude oils. Considering the maturity relationships, it was suggested that the bulk composition of Wafra/Iucene crude oil was altered due to biodegradation and vertical migration. Correlation between API gravity and PAP of aromatic fraction indicated two maturity levels of onshore and offshore oil fields. The distribution of n-alkanes reflected the marine origin of the crude oils. Isoprenoids/n-alkanes and pristane/phytane ratios were determined by capillary GC of a middle distillate of the crude oil samples. The correlations showed that the oil samples, except for those collected from Wafra oil field, are normal mature crude oils which were deposited under oxidizing environments. The much lower Pr/Ph ratio of Wafra/Iucene oil field could be considered as an indicator of reducing depositional environments.     

BULK COMPOSITION OF SOME SAUDI ARABIAN CRUDE OILS IN RELATION TO MATURATION,ORIGIN AND DEPOSITIONAL ENVIRONMENTS

ABSTRACT

Ten crude oil samples, covering wide range of maturity (API = 18.5?36.1), were assembled from Safaniya, Abqiq, Ain-Dar, Wafra, Marjan, and Zulf oil fields in the area of Arabian Gulf. Different analytical techniques, including liquid chromatographic separation, gas chromatography, and nuclear magnetic resonance spectroscopy, were used to characterize the oil samples. Some bulk and specific compositional parameters were used for oil-oil correlations in order to evaluate thermal maturation, origin, biodegradation and depositional environments of the crude oils. Considering the maturity relationships, it was suggested that the bulk composition of Wafra/Iucene crude oil was altered due to biodegradation and vertical migration. Correlation between API gravity and PAP of aromatic fraction indicated two maturity levels of onshore and offshore oil fields. The distribution of n-alkanes reflected the marine origin of the crude oils. Isoprenoids/n-alkanes and pristane/phytane ratios were determined by capillary GC of a middle distillate of the crude oil samples. The correlations showed that the oil samples, except for those collected from Wafra oil field, are normal mature crude oils which were deposited under oxidizing environments. The much lower Pr/Ph ratio of Wafra/Iucene oil field could be considered as an indicator of reducing depositional environments.     

BIOMARKER GEOCHEMISTRY OF CRUDE OILS FROM THE QAIDAM BASIN, NW CHINA

A suite of 16 crude oil samples from 13 oilfields in the Qaidam Basin were analyzed using techniques including gas chromatography and gas chromatography - mass spectrometry. Biomarker compositions and parameters were used to investigate the palaeoenvironmental and depositional conditions and to correlate the oils with eachother. Oils from the western Qaidam Basin have pristane/phytane (Pr/Ph) ratios of less than 0.7, and contain abundant gammacerane, C₂₇ steranes, 4-methyl steranes and long-chain tricyclic terpanes. C₂₉ sterane 20S/(20S+20R) and ββ/(ββ+αα) ratios show that the western Qaidam oils have variable maturities ranging from immature to mature. Oils from the northern Qaidam Basin, by contrast, have Pr/Ph ratios greater than 3, low gammacerane contents, and relatively abundant C₂₉ steranes, bicyclic terpanes and alkylcyclohexanes. C₂₉ sterane 20S/(20S+20R) and ββ/(ββ+αα) ratios indicate that the northern Qaidam oils are mature.
δ¹³C values, which range from -25.4‰ to -28.3‰ with the exception of one oil from the north (-3l.6‰), are similar for oils from both the northern and western parts of the Qaidam Basin. The oils'carbon isotope compositions are similar to those of the organic matter in potential source rocks.
The western Qaidam oils are inferred to have originated from Tertiary source rocks deposited under anoxic and saline-hypersaline lacustrine conditions with dominant algal organic matter. The northern Qaidam oils are interpreted to be derived from Jurassic source rocks which were deposited in a freshwater lacustrine environment and which are dominated by terrigenous organic matter.     

Significance of thiophenic compounds distribution in correlating crude oils into source related types

Gas chromatography and combined gas chromatography/mass spectrometry were used to characterize different thiophenic compounds in representative petroleum from the Gulf of Suez. An evaluation of the distribution patterns of these compounds has been used to infer depositional environment and lithology of crude oil source rock and maturity. Ratios involving dibenzothiophenes (DBT) such as DBT/phenanthrene (Phen) and methyldibenzothiophenes (MDBT)/methylphenanthrenes (MPhen) correlated with other biological markers and were used to classify the oils into different source-related types. Type 1 oils with relatively high (DBT/Phen) and (MDBT/MPhen) ratios show marine carbonate depositional setting. Type 2 oils show low (DBT/Phen) and (MDBT/MPhen) ratios and other biomarker features consistent with marine siliciclastic source rocks. On the other hand, type 3 oils have geochemical characteristics intermediate between those of types 1 and 2.     

塔河油田原油生物标志物定量特征研究

通过对塔河地区22个原油样品的饱和烃色质、芳烃色质和饱和烃色谱的定量分析研究表明,塔河地区中南部和东部原油的二苯并噻吩和姥鲛烷含量高于中北部地区的原油,说明前者代表碳酸盐沉积环境,而后者的缺氧程度更大;中北部地区原油的C35升藿烷含量高于东南部地区的原油,说明水体分层更明显,其还原程度更强;C29S构型甾烷含量越低,二苯并噻吩含量和2-甲基菲+3-甲基菲含量越高,原油的成熟度越高;中北部地区原油的25-降藿烷和二降藿烷含量高,为生物降解原油。     

烃源岩和油气中有机含硫化合物的生成、分布及应用

有机含硫化合物在烃源岩和原油中广泛分布,包含丰富的地球化学信息。综述了有机含硫化合物的分析测试,成岩作用阶段有机含硫化合物的生成,以及有机含硫化合物在烃源岩和油气中的来源和分布规律。有机含硫化合物在判识沉积环境和有机质的成熟度,示踪油气充注路径,应用于油源对比以及指示硫酸盐热化学还原作用（TSR）过程等方面具有广泛的应用价值。有机含硫化合物结构种类复杂,不同沉积环境和岩相以及成熟度的沉积有机质和原油中组成有很大差异。油气形成和不同演化阶段中新有机含硫化合物结构的准确鉴定和单体有机硫同位素的测定,将有助于更好地认识和理解有机含硫化合物在烃源岩和原油中的分布特征及作用,建立新的地球化学指标或指示剂。另外,不同地质条件下有机硫与无机硫之间的相互作用对有机含硫化合物硫同位素组成的影响是未来研究工作的重点方向之一。     

MATURATION AND DEPOSITIONAL ENVIRONMENTS OF CRUDE OILS FROM GULF OF SUEZ

Crude oil samples from the major producing fields in the Gulf of Suez were geochemically assessed to evaluate maturity, origin and depositional environmental trends. Multiple analytical parameters used to charactrizethe petroleum samples included asphaltene content, sulfur content, liquid chromatographic separation, and gas chromatography of the saturated hydrocarbons fraction. From the results obtained, it was suggested that the crude oils are mature. Also, no strong evidence of biodegradation has been observed. Distribution of n-alkanes indicated that the crude oils are derived mainly from marine sedmentary source rocks. Pristane/phytane ratio of the crude oils seemed to be mostly below unity, indicating reducing depositional environments.     

塔里木原油含硫化合物的地球化学意义

塔里木盆地30余个代表性原油芳烃组分的色质和色谱－原子发射光谱分析资料表明,不同成因原油的含硫化合物含量和分布明显不同。与陆相原油相比,海相原油以高二苯并噻吩系列(>20%)、高DBT/P(>0.35)为特征,其中,塔中局限性海湾相原油以这两参数值更高而与塔北台地相原油形成区别；在二苯并噻吩系列内分布上,它们的DBT少而DMDBT丰富,反映出成油母质沉积环境性质的差别。来源于不同岩性源岩的原油中苯并噻吩系列相对于二苯并噻吩系列的含量不同,在碳酸盐岩原油中较高。      

Geochemical investigation of trace elements in crude oils from two different depobelts in the Niger Delta basin,Nigeria

The concentrations of trace elements in crude oil samples from the Northern and Central swamps depobelts in the Niger Delta basin were investigated using Flame Atomic Absorption Spectrometer. The origin, source facies, and depositional environment of organic matter that produced the oils were determined based on the trace elements concentrations. The concentrations of the trace elements (Cr, Cu, Fe, Mn, Ni and V) ranged from 0.04 to 5.71 ppm. Iron is the most abundant element in the samples while Cr has the least concentration. The results from trace metal geochemistry showed that the Niger Delta oils were derived predominantly from terrestrial organic matter deposited in the oxic depositional environment. The concentrations and ratios of nickel and vanadium grouped the oils into two distinct families reflecting the depobelt the oils belong. This observation indicates that the source rocks in the two depobelts were formed from organic matter of different source facies.     

Origin of Bahariya oil in Salam oil field,Western Desert- Egypt

The origin of Bahariya oil is a debatable issue. Bahariya Formation produces oil from the Lower sandstone unit by normal pressure mechanism, while the Upper Bahariya shale produces oil by fracking mechanism. The main question is: is there any genetic relationship between the two oils.To answer this question, “50” ditch samples, “12” extract samples and “2” oil samples represent Khatatba and Bahariya formations and Abu Roash ‘G’ Member, collected from six wells drilled in Salam oil field, have been geochemicaly analyzed, using LECO SC632, Rock–Eval- 6 pyrolysis, GC and GC/MS techniques.The analysis shows that the Total Organic Carbon content (TOC) for the studied formations ranges from fair to v.good, with poor to good hydrocarbon potentiality. The maturity evaluation using Tmax, and calculated Vitrinite reflectance (R_o) showed that the studied samples have good thermal maturation reaching the stage of oil generation. Also the analysis revealed that the kerogen is a mixture of type II/III kerogen, reflecting the potential generation of oil and gas. The GC and GC/MS data showed that the organic matter is a mixed marine/terrestrial input deposited in transitional environment under prevailing reducing conditions. The oil samples fingerprint of the saturated hydrocarbons fraction from Baharyia reservoir (Lower and Upper) members suggest that the oil samples have a mixed organic source with significant terrestrial organic matter input deposited under saline to hypersaline environment with slightly oxidizing environment.Based on the obtained results, it is suggested that the Bahariya oil has been sourced mainly from deeper horizons (Khatatba Formation) with some contribution from upper and lower Bahariya source rocks.     

OILS FROM CENOZOIC RIFT-BASINS IN CENTRAL AND NORTHERN THAILAND: SOURCE AND THERMAL MATURITY

Oil is produced from the Suphan Buri, Phitsanulok and Fang Basins onshore central and northern Thailand. Most of the Cenozoic rift‐basins onshore Thailand are 2–4 km deep, but the Phitsanulok Basin is the deepest with a basin‐fill up to 8 km thick. In this basin, the Sirikit field produces ～18,000–24,000 bbl/day of crude oil. In the Suphan Buri Basin, about 400 bbl/day of crude oil is produced from the U Thong and Sang Kajai fields. Approximately 800 bbl/day of crude oil is produced from the Fang field (Fang Basin), which in reality consists of a number of minor structures including Ban Thi, Pong Nok, San Sai, Nong Yao and Mae Soon. A total of eight oil samples were collected from these structures and from the Sirikit, U Thong and Sang Kajai fields. The oils were subjected to MPLC and HPLC separation and were analysed by gas chromatography (GC) and gas chromatography‐mass spectrometry (GC‐MS and GC‐MS‐MS). The U Thong oil was investigated in more detail by separating the oil into a number of fractions suited for the analysis of various specific compounds. The Sirikit oil appears to be the most mature, whereas the Suphan Buri oils and the oil from the San Sai structure (Fang Basin) are the least mature. Apart from the San Sai oil, the other oils in the Fang Basin are of similar maturity. The oils contain small amounts of asphaltenes and the asphaltene‐free fractions are completely dominated by saturated hydrocarbons (generally >60%). Long‐chain n‐alkanes extend to at least C₄₀ and the oils are thus highly waxy. In general the oils were generated from freshwater lacustrine source rocks containing a large proportion of algal material, as indicated by the presence of long‐chain n‐alkanes, low C₃₁22R/C₃₀ hopane ratios, the presence of 28‐Nor‐spergulane, T26/T25 (tricyclic triterpanes) ratios of 1.07–1.57 and tetracyclic polyprenoid (TTP) ratios close to 1. Occasional saline conditions may have occurred during deposition of the Sirikit, Ban Thi and Pong Nok source rocks. The Fang Basin oils were sourced from two different kitchens, one feeding the Ban Thi and Pong Nok structures and one feeding the Mae Soon, Nong Yao and San Sai structures. The presence ofcadalene, tetracyclic C₂₄ compounds, oleanane, lupane, bicadinane and trace amounts ofnorpimarane or norisopimarane indicate a contribution from higher land plant organic matter to the oils. The terrestrial organic matter may occur disseminated in the lacustrine facies or concentrated in coal seams associated with the lacustrine mudstones. Thermally immature oil shales (lacustrine mudstones) and coals exposed in numerous basins in central and northern Thailand could upon maturation generate oils with a composition comparable to the investigated oils.     

SOURCE ROCK–DEPENDENT BIOMARKER PROPERTIES AND STABLE CARBON ISOTOPE COMPOSITION OF CRUDE OILS FROM WEST BAKR FIELDS,ONSHORE GULF OF SUEZ,EGYPT: A CASE STUDY

Four representative crude oil samples from three different pay zones (Ayun, Yusr and Bakr members) of Lower Miocene age from West Bakr Fields K, H and M, Gulf of Suez, Egypt were analyzed to evaluate the source rocks and their depositional environments. The saturate and aromatic fractions were subjected to a variety of organic geochemical analyses including Gas Chromatography (GC), Gas Chromatography-Mass Spectrometry (GC-MS), trace element analyses (V, Ni, Co, Cr, Fe, Mg, Mn, Ca and Zn) and stable carbon isotopic composition δ¹³C. The geochemical characteristics and biomarker properties of the studied crude oils show no obvious variations. All the studied crude oil samples are of naphthenic base and possess similar values of V/Ni ratio, suggest that the studied crude oils might be derived from the same source rocks. Moreover the ratios of Ts/Tm (< 1), Oleanane index (> 30%) and gammacerane index (> 20%) reflect a marine environment with minor terrestrial higher plants input from Tertiary source rocks deposited in high salinity waters with less reducing conditions. The enrichment of stable carbon isotopic composition δ¹³C to the saturate fraction ranges from (?29.1 to?29.35‰ PDB); and to the aromatic fraction ranges from (?28.35 to?28.60‰ PDB) is observed. The isotopic values together with the calculated canonical variable (CV) of the studied crude oil samples < 0.47, which further support that the crude oils of West Bakr Fields were generated from marine source environment. The achieved results obtained from the geochemical characteristics of the studied crude oils suggest marine environment with minor terrestrial higher plants input from source rocks of Tertiary age. These are likely to be interval within the Lower Miocene Rudeis shale and Eocene Thebes Formation carbonate rocks where the vertical and horizontal migration caused the oil to be entrapped within the sandstone of Lower Miocene age.