Oil-source Correlation Research Articles

Bicyclic alkanes in source rocks of the Triassic Yanchang Formation in the Ordos Basin and their inconsistency in oil-source correlation

The Triassic Yanchang Formation is the main source rocks for Mesozoic oil in Ordos Basin. The formation includes 10 oil-bearing beds (Ch 1–Ch 10), that each can be further divided into two to three intervals. Abundant C12–C14 and C15–C16 bicyclic alkanes have been detected in the formation in the Xifeng oilfield, Ordos Basin. The C12–C14 group is dominated by C12 and C13, and the C15–C16 group contains abundant C15. The groups show three distribution patterns: A) the C12–C14 group is the major component in the non-source rocks of the Ch 7-1 and Ch 8-1 intervals; B) both groups are abundant and are common in source rocks of the Ch 7-3 interval; and C) the C15–C16 group is the major component in source rocks of the Ch 7-3 interval and also in sediments that contain type Ⅰ or partial sapropel type Ⅱ1 organic matter (OM) in the Ch 7-2 and Ch 8-1 intervals. Although thermal maturities of the source rocks in the Ch 7 section are similar, they show significant differences with respect to the drimane isomerisation index, which indicates that the drimane rearrangement is controlled by thermal evolution of the sediments, but may also be closely related to the depositional environment. This study determined that reducing environments are more conducive to preservation of drimane than oxic environments. The drimane isomerisation index and the value of the hopane parameter Tm/Ts are positively correlated. The parameter Tm/Ts varies over a wide range within the sequence, and the large variations may be a result of terrigenous OM input by turbidity currents and/or gravity flows, mixed with the autochthonous sediments. Abundant homodrimane in both source rocks may reflect reducing environments in deep lakes and major input of higher plant OM. Organic-rich shale and oil shale in the Ch 7-3 interval of the Yanchang Formation are the primary sources of oil in reservoirs in the Xifeng area. The crude oil is rich in bicyclic alkanes that are dominated by C15–C16 as source rocks with pattern C for bicyclic alkanes, which indicates an origin mainly from the Ch 7-3 interval. The main peaks in all of the crude oils are associated with 8β(H)-drimane and lower abundance of rearranged drimane. However, most of the source rocks have a main peak associated with 8β(H)-homodrimane or rearranged drimane. Weak microbial action, selective degradation and water washing may be the cause of the significant difference in bicyclic sesquiterpane composition between the crude oil and the source rocks. The result suggests that oil-source correlations based on the bicyclic sesquiterpanes are questionable.

Secondary migration of hydrocarbons in the Zhujiang Formation in the Huixi half-graben, Pearl River Mouth Basin, South China Sea

The process and mechanisms of secondary hydrocarbon migration in the Huixi half-graben, Pearl River Mouth Basin, were investigated on the basis of geological analysis of the strata and study of the porosity and permeability of the reservoir rocks, fluid potential, oil properties, and geochemistry of oil–source correlation. The results suggest that the hydrocarbons of the Zhujiang Formation in the Huixi half-graben were derived from source rocks of the Eocene Wenchang Formation and the Eocene–Oligocene Enping Formation in the Huizhou Sag. The hydrocarbons migrated laterally from northeast to southwest. The sandstone in the upper member of the Zhujiang Formation exhibited superior physical properties (porosity and permeability) and connectivity than the lower member. Thin sandstone beds with good physical properties and stable distribution in the upper member of the Zhujiang Formation were the main carrier beds for lateral hydrocarbon migration.

Geochemical characteristics and oil-source correlation in offshore regions

ABSTRACTTraditional geochemical methods to correlate oil and source are not quite fit for too many layers in steep offshore regions. Therefore, more biomarkers and new methods are needed to finish more complicated correlations. Resources in Chengbei Beach zone are generally shallow and high-quality light oil. There are two hydrocarbon source sags and many oil-source layers, and the sources are still disputed. More parameters are used to correlate oil source (i.e., relative group compositions, δ13C, steroids, hopanes, and terpenoids). Some special methods are found, such as the triangular chart of aromatic, asphalt, and saturated hydrocarbon, and the comprehensive use of gammacerane, hopance, and tricyclic terpanes. It is found that there are mainly three oil types. The first type mainly derives from source rocks in Es3, the second type from Es1, and the third type is their mixture. These three oil types are found to have regional features.

Oil–source rock correlation for tight oil in tuffaceous reservoirs in the Permian Tiaohu Formation, Santanghu Basin, northwest China

Tight oil in the Permian Tiaohu Formation in the Santanghu Basin, northwest China, has a peculiar property such that the reservoir is sedimentary organic matter-bearing tuff characterized by high porosity (10%–25%) and very low permeability, mainly in the range of 0.01–0.50 mD. Biomarker and stable carbon isotope compositions of selected crude oils and source-rock extracts were analyzed to determine the source rock of the tight oil. Source rocks in the Lucaogou Formation consist of various rock types dominated by mudstones containing organic matter with intense yellow–green fluorescence. Mudstones in the Lucaogou Formation have total organic carbon (TOC) values mainly in the range of 1.0–8.0 wt%, hydrocarbon generation potential (S1+ S2) mostly >6 mg/g, and chloroform extractable bitumen “A” generally >0.1%. The maceral composition is predominantly fluorescing amorphinite. The hydrogen index (HI) varies from 300 to 900 mg HC/g TOC, indicating dominant Type I and Type II kerogen. Compared with the mudstones and tuffs in the Tiaohu Formation, the mudstones in the Lucaogou Formation are the best source rocks. The biomarker characteristics of mudstone extracts in the Lucaogou Formation differ from those in the Tiaohu Formation, based on the gammacerane index, β-carotane content, and the relative contents of C27, C28, and C29regular steranes. Crude oil samples in the tuff show low pristane/phytane (Pr/Ph) ratios, high gammacerane indices, high β-carotane, and a dominance of the C29regular sterane followed by C28and C27steranes, as well as depleted stable carbon isotope compositions. Oil–source correlation with biomarkers and δ13C values shows that the crude oil in the tuffs mainly originates from underlying source rocks in the Lucaogou Formation. The sedimentary organic matter in the tuffs also makes a small contribution to the tuffaceous reservoir. Therefore, the tuffaceous tight reservoir in the Tiaohu Formation is unusual in that the oil is not indigenous; rather, it migrates a long distance to accumulate in the upper reservoir.

Oil-source correlation of Lower-Triassic oil seepages in Ni’erguan village, Southern Guizhou Depression, China

There are abundant bitumens and oil seepages stored in vugs in a Lower-Triassic Daye formation (T1d) marlite in Ni’erguan village in the Southern Guizhou Depression. However, the source of those oil seepages has not been determined to date. Multiple suites of source rocks of different ages exist in the depression. Both the oil seepages and potential source rocks have undergone complicated secondary alterations, which have added to the difficulty of an oil-source correlation. For example, the main source rock, a Lower-Cambrian Niutitang Formation (Є1n) mudstone, is over mature, and other potential source rocks, both from the Permian and the Triassic, are still in the oil window. In addition, the T1d oil seepages underwent a large amount of biodegradation. To minimize the influence of biodegradation and thermal maturation, special methods were employed in this oil-source correlation study. These methods included catalytic hydropyrolysis, to release covalently bound biomarkers from the over mature kerogen of Є1n mudstone, sequential extraction, to obtain chloroform bitumen A and chloroform bitumen C from the T1d marlite, and anhydrous pyrolysis, to release pyrolysates from the kerogen of T1d marlite. Using the methods above, the biomarkers and n-alkanes released from the oil samples and source rocks were analysed by GC–MS and GC-C-IRMS. The oil-source correlation indicated that the T1d oil seepage primarily originated from the Є1n mudstone and was partially mixed with oil generated from the T1d marlite. Furthermore, the seepage also demonstrated that the above methods were effective for the complicated oil-source correlation in the Southern Guizhou Depression.

Geochemical significance of 17α(H)-diahopane and its application in oil-source correlation of Yanchang formation in Longdong area, Ordos basin, China

Relatively high abundance of 17α(H)–C30 rearranged hopane has been detected in some oils and rock extracts from Yanchang Formation of Longdong area, southwestern Ordos basin. Oil shale, silty mudstone and carbonaceous mudstone extracts from Yanchang Formation all have low abundance of C30 rearranged hopane, while high concentrations of C30 rearranged hopane were observed in the dark mudstone extracts. Analysis on the geochemical parameters of the organic matter origin, thermal maturity, and sedimentary organic facies were carried out. The result showed that the depositional-redox environment and lithology may be the critical factors for the rearrangement of hopanes which usually occurred in suboxic condition with clay-catalyzed reactions, as is consistent with the viewpoint of Peters and Moldowan (1993). According to the relative abundance of diahopane, three oil classes can be identified. Class 1 oil with low abundance of diahopanes was originated from oil shale of Chang 7 member, while Class 2 oil and Class 3 oil with middle to high abundance of diahopanes were derived from dark mudstones of Chang 4 + 5 to Chang 9 members of Yanchang Formation. Of the 151 analyzed oil and extracts samples from different stratigraphic intervals, 105 samples belong to Class 1 oil coming from oil shale, while 46 samples belong to Class 2 and Class 3 oil derived from mudstones. So oil shale of Chang 7 member is the main effective source rock of Longdong area, and dark mudstones of Chang 4 + 5 to Chang 9 member are also important source rocks.

Pyrolytically Derived Polycyclic Aromatic Hydrocarbons in Marine Oils from the Tarim Basin, NW China

Polycyclic aromatic hydrocarbons (PAHs) in oils from the cratonic region of the Tarim Basin have been characterized by gas chromatography–mass spectroscopy to investigate their origins and geochemical applications. PAHs dominated by unsubstituted components together with pyrolytically derived components such as anthracene, fluoranthene, benzoanthracene, benzofluoranthenes and benzopyrenes occur in some oils represented by those from well TD2. The widespread spatial and temporal occurrence of igneous activity within the Palaeozoic succession in the Tarim Basin makes the derivation of the latter PAHs from pyrolytic sources probable. Exposure to high temperatures results in the pyrolysis of the oil reservoir, adding high-temperature aromatic artifacts to the oil. Geochemical measurements show the wide occurrence of mixing processes between pyrolytically derived PAHs and diagenetically derived hydrocarbons. Good preservation of pyrolytic PAHs in oils from well TD2 and a few other wells is because they are less affected by late charge and dilution processes. However, these pyrolytically derived PAHs in conjunction with the bulk carbon isotopic compositions have been commonly misinterpreted in oil-source correlations. Only oils from well TD2 and a few other wells have been correlated to the Cambrian source rocks because of the wrong selection of end members. When the effects from the rapid heating of organic material by magmatic intrusions and/or hydrothermal fluid activity are properly accounted for, confusion in oil-source correlations may potentially be resolved and the contribution from the Cambrian strata can appropriately be assessed.

The origin and distribution of crude oil in Zhu III sub-basin, Pearl River Mouth Basin, China

The origin of thirteen major oil fields in Zhu III sub-basin, Pearl River Mouth Basin, was studied by using the results of Rock-Eval pyrolysis on 340 samples and biomarker analysis on 18 source rock samples and 33 oil samples. The two possible source rock intervals have different biomarker assemblages and were deposited in different environments. The Eocene Wenchang Formation (E2w, 49.5–35 Ma) is characterized by high hopane/sterane ratio (>37.84), high 4-methyl sterane index (0.28–1.06), low gammacerane index (<0.09), low extended tricyclic terpane ratio [ETR=(C28 + C29)/(C28+C29 + Ts), 0.13–0.20] and bicadinane/C30 hopane (<0.02), which was deposited in fresh-brackish water and dominated by algae. On the contrary, Oligocene Eenping Formation (E3e, 35–30 Ma) has high gammacerane index (>0.10), high bicadinane/C30 hopane (up to 73.62) but low hopane/sterane ratio (<12.50), and it was deposited in relative saline water environment with significant high terrestrial plant debris input. Because of complex geologic settings, oils have different distribution. By using oil-source correlation analysis and hierarchical cluster analysis, two source-related oil groups were identified. Oils found in the Wenchang A depression and Yangjiang uplift, which are classified to oil group 1, were derived from E3e. Oils found in the Wenchang B depression and Shenhu uplift, which are classified to oil group 2, were derived from both E2w and E3e source rocks. But the Qionghai uplift received supply from both the Wenchang A and B depression. This distribution pattern is also proven by using a simple three-dimensional model called PathWay™. An explanation was put forward in this paper about the oils in Zhu III sub-basin and four potential petroleum accumulations were roughly predicted where no well drilled.

Evaluating rare earth elements as a proxy for oil–source correlation. A case study from Aer Sag, Erlian Basin, northern China

The use of rare earth elements (REE) for oil–source correlation has not yet been established. In order to evaluate the potential of REE as proxies for oil–source correlation, we used traditional correlation approaches, including biomarkers and trace elemental ratios (V/Ni and Ni/Co), to identify the source rock of oil sands using isolated organic extracts of mudstones and oil sands, and by analyzing the organic extracts and their corresponding whole rock material for REE compositions by inductively coupled plasma-mass spectrometry (ICP-MS). Oil–source correlations using REE were not consistent with conclusions based on biomarker data and trace element ratios. Only one pair of oil–source rock relationship was successfully established using REE. REE concentrations of crude oils could possibly be controlled by the quantities of metal complexes and functional groups that provide complexing sites for V and REE as well as secondary alteration processes (e.g., thermal alteration and biodegradation). REE patterns might be linked to the organic matter types of source rocks. Although an accurate oil–source relationship failed to be established using REE in this study, REE could potentially be a novel complementary proxy for oil–oil and/or oil–source correlations when supplemented by traditional correlation approaches, including biomarkers.

Oil/gas–source rock correlations in the Dniepr-Donets Basin (Ukraine): New insights into the petroleum system

The Dniepr-Donets Basin (DDB) hosts a multi-source petroleum system with more than 200 oil and gas fields, mainly in Carboniferous clastic rocks. Main aim of the present study was to correlate accumulated hydrocarbons with the most important source rocks and to verify their potential to generate oil and gas. Therefore, molecular and isotopic composition as well as biomarker data obtained from 12 oil and condensate samples and 48 source rock extracts was used together with USGS data for a geological interpretation of hydrocarbon charging history.Within the central DDB, results point to a significant contribution from (Upper) Visean black shales, highly oil-prone as well as mixed oil- and gas-prone Serpukhovian rocks and minor contribution from an additional Tournaisian source. Devonian rocks, an important hydrocarbon source within the Pripyat Trough, have not been identified as a major source within the central DDB. Additional input from Bashkirian to Moscovian (?) (Shebelinka Field) as well as Tournaisian to Lower Visean rocks (e.g. Dovgal Field) with higher contents of terrestrial organic matter is indicated in the SE and NW part, respectively.Whereas oil–source correlation contradicts major hydrocarbon migration in many cases for Tournaisian to Middle Carboniferous reservoir horizons, accumulations within Upper Carboniferous to Permian reservoirs require vertical migration up to 4000 m along faults related to Devonian salt domes.1-D thermal models indicate hydrocarbon generation during Permo-Carboniferous time. However, generation in coal-bearing Middle Carboniferous horizons in the SE part of the basin may have occurred during the Mesozoic.

Key elements controlling oil accumulation within the tight sandstones

Tight oil sandstone reservoirs with low porosity and permeability, which are an unconventional petroleum resource, have been discovered in the Jurassic intervals of the central Junggar Basin, the northwestern China. To reveal the accumulation mechanism, a relatively comprehensive research was conducted, including oil-source correlation, porosity evolution, and hydrocarbon charging history. The results show that crude oil of these tight sandstone reservoirs were mainly from Permian source rocks with some contribution from Jurassic source rocks. The reservoirs were buried at shallow depth ( 5%). In contrast, the sandstone reservoir had already become tight and did not provide available space to accumulate oil due to severe compaction and cementation when hydrocarbon from Jurassic source rock filled, evidenced by low GOI values (<5%). Therefore, reservoir porosity controls the oil accumulation within tight sandstone. Whether tight sandstone reservoirs accumulate oil depends on the reservoir quality when hydrocarbons charge. Before the exploration of tight oil sandstone reservoirs, it should be required to investigate the relationship between oil charging history and porosity evolution to reduce the exploration risk and figure out the available targets.

Insight into unresolved complex mixtures of aromatic hydrocarbons in heavy oil via two-dimensional gas chromatography coupled with time-of-flight mass spectrometry analysis

The aromatic hydrocarbon fractions of five crude oils representing a natural sequence of increasing degree of biodegradation from the Liaohe Basin, NE, China, were analyzed using conventional gas chromatography–mass spectrometry (GC–MS) and comprehensive two-dimensional gas chromatography (GC×GC). Because of the limited peak capability and low resolution, compounds in the aromatic fraction of a heavily biodegraded crude oil that were analyzed by GC–MS appeared as unresolved complex mixtures (UCMs) or GC “humps”. They could be separated based on their polarity by GC×GC. UCMs are composed mainly of aromatic biomarkers and aromatic hydrocarbons with branched alkanes or cycloalkanes substituents. The quantitative results achieved by GC×GC-FID were shown that monoaromatic hydrocarbons account for the largest number and mass of UCMs in the aromatic hydrocarbon fraction of heavily biodegraded crude oil, at 45% by mass. The number and mass of diaromatic hydrocarbons ranks second at 33% by mass, followed by the aromatic biomarker compounds, triaromatic, tetraaromatic, and pentaaromatic hydrocarbons, that account for 10%, 6%, 1.5%, and 0.01% of all aromatic compounds by mass, respectively. In the heavily biodegraded oil, compounds with monocyclic cycloalkane substituents account for the largest proportion of mono- and diaromatic hydrocarbons, respectively. The C4-substituted compounds account for the largest proportion of naphthalenes and the C3-substituted compounds account for the largest proportion of phenanthrenes, which is very different from non-biodegraded, slightly biodegraded, and moderately biodegraded crude oil. It is inferred that compounds of monoaromatic, diaromatic and triaromatic hydrocarbons are affected by biodegradation, that compounds with C1-, C2-substituents are affected by the increase in degree of biodegradation, and that their relative content decreased, whereas compounds with C3-substituents or more were affected slightly or unaffected, and their relative content also increased. The varying regularity of relative content of substituted compounds may be used to reflect the degree of degradation of heavy oil. Moreover, biomarkers for the aromatic hydrocarbons of heavily biodegraded crude oil are mainly aromatic steranes, aromatic secohopanes, aromatic pentacyclotriterpanes, and benzohopanes. According to resultant data, aromatic secohopanes could be used as a specific marker because of their relatively high concentration. This aromatic compound analysis of a series of biodegraded crude oil is useful for future research on the quantitative characterization of the degree of biodegradation of heavy oil, unconventional oil maturity evaluation, oil source correlation, depositional environment, and any other geochemical problems.

利用三环萜烷对比泌阳凹陷生物降解油油源

Abstract Biodegraded oils from the northern slope of the Biyang Sag were analyzed to examine the application of tricyclic terpanes to biodegraded oil-source correlation. Tricyclic terpanes are resistant to biodegradation ( biodegradation rank 8) . New tricyclic terpane parameters, such as (C23-C26/Cl9-C22)-tricyclic terpanes, (Cl9-C26/ C28-C29)-tricyclic terpanes and (C19-C26)-tricyclic terpanes/C29-Ts are effective oil-source correlation parameters. Correlation results suggested that the biodegraded oils in the lower member of Eh 3 on the northern slope of the Biyang Sag came from the mudstones in the lower member of Eh 3 of the central sag, and the oils in the upper member of Eh 3 mainly came from the mudstones in the upper member of Eh 3 of the central sag. The correlation results of oils and source rocks in the Zhu I Depression of the Pearl River Mouth Basin determined by the three tricyclic terpane parameters were consistant with previous results, further supporting the effectiveness of the parameters.

Correlation of Oils and Source Rocks in Marun Oil Field in the South West of Iran: Using Biomarkers

Biomarkers study is one useful tool for oil-oil and oil-source correlations in any petroleum field. Molecular markers were used together with stable carbon isotopes to constrain genetic relationships between oils and potential source rocks in the Marun oil field. The Marun oil field is one of the giant oil fields in south west of Iran. It consists of two oil reservoirs named Asmari and Bangestan. This article presents the correlation of Asmari and Bangestan oil reservoirs with probable source rocks named Pabdeh, Kazhdomi, and Garau formations. Distribution patterns of different biomarkers, such as Hopanes and Steranes (obtained by gas chromatography-mass spectrometry), were used to correlate oils and source rocks. The results show that there is an obvious similarity in distribution patterns of all biomarkers between Kazhdomi formation and oil samples as compared with Pabdeh and Garau formations. Furthermore, stable carbon isotope shows that in contrast to Pabdeh and Garau formations, the carbon isotope range of Kazhdomi formation had a good overlaying with Asmari and Bangestan oil reservoirs. The result of this study shows Kazhdomi formation as a proper source rock of oil in the Marun oil field.

Evidence of Oil Sources and Migration in Triassic-Jurassic Reservoirs in the South Tianhuan Depression of the Ordos Basin, China Based on Analysis of Biomarkers and Nitrogen-Bearing Compounds

The Ordos Basin is an important intracontinental sedimentary basin in western China for its abundant Mesozoic crude oil resources. The southern part of the Tianhuan Depression is located in the southwestern marginal area of this Basin, in which the Jurassic and Triassic Chang-3 are the main oil-bearing strata. Currently, no consensus has been reached regarding oil source and oil migration in the area, and an assessment of oil accumulation patterns is thus challenging. In this paper, the oil source, migration direction, charging site and migration pathways are investigated through analysis of pyrrolic nitrogen compounds and hydrocarbon biomarkers. Oil source correlations show that the oils trapped in the Jurassic and Chang-3 reservoirs were derived from the Triassic Chang-7 source rocks. The Jurassic and Chang-3 crude oils both underwent distinct vertical migration from deep to shallow strata, indicating that the oils generated by Chang-7 source rocks may have migrated upward to the shallower Chang-3 and Jurassic strata under abnormally high pressures, to accumulate along the sand bodies of the ancient rivers and the unconformity surface. The charging direction of the Jurassic and Chang-3 crude oils is primarily derived from Mubo, Chenhao, and Shangliyuan, which are located northeast of the southern Tianhuan Depression, with oils moving toward the west, southwest, and south. The results show that an integration of biomarker and nitrogen-bearing compound analyses can provide useful information about oil source, migration, and accumulation.

Origin and occurrence of crude oils in the Zhu1 sub-basin, Pearl River Mouth Basin, China

The origin of the seventeen major oil fields in the Zhu1 sub-basin, Pearl River Mouth Basin (PRMB) was studied based on the results of Rock–Eval pyrolysis on more than 370 samples and biomarker analysis on 31 source rock samples and 63 oil samples. The two possible source rock intervals have different biomarker assemblages and were deposited in different environments. The Wenchang Formation (E2w, 56.5–32Ma) is characterized mainly by low C19/C23 tricyclic terpane (<2.0), low C24 tetracyclic terpane/αβC30 hopane (<0.06), low bicadinane-T/αβC30 hopane (<2.0) and high 4-methyl steranes/∑C29 steranes (most >0.4) ratios, and were deposited in anoxic to suboxic environments with important contribution from Pediastrum and Dinoflagellates. The Enping Formation (E3e, 32–30Ma) has high C19/C23 tricyclic terpane, high C24 tetracyclic terpane/αβC30 hopane, widely variable yet overally high bicadinane-T/αβC30 hopane and low 4-methyl steranes/∑C29 steranes ratios, and were deposited in freshwater lacustrine to swamp conditions with significant terrigenous organic matter input. According to oil-source correlation, three oil classes can be identified in the Zhu1 sub-basin. Class 1 oil is E2w-derived and occurs widely. Class 2 oil is E3e-derived and refers to oils from F field in the north of the Huizhou depression. Class 3 oil is a mixture of oils generated from E2w and E3e, only distributed in the Huizhou depression and on its southern margin. The petroleum distribution pattern is mainly controlled by the distribution of source rocks and the migration pathways of oils. This research has important implications for future exploration.

Hydrocarbon potential of Sargelu Formation and oil-source correlation, Iraqi Kurdistan

Sargelu Formation is one of the major petroleum source rocks in Iraq and the Middle East. In an effort to build on the previous work and add new interpretations, this investigates selected outcrops, bore holes, and crude oil samples from different localities in Iraqi Kurdistan. Sargelu Formation has rather uniform lithology with variable thickness throughout Iraqi Kurdistan. The thickness progressively decreases from about 485 m west of the Tigris River in the Mosul area toward north where it is 20–30 m thick and northeastern Iraq where it is about 50 m thick. Results of the studied samples show that the total organic carbon of Sargelu Formation decreases toward the north and northeastern parts of Iraq. The mean of total organic carbon (TOC) wt% is 11.1 in northwestern part in Tawke-15, and it is only 0.5 wt% in eastern part in Hanjeera locality. The organic material is characterized by type II and III kerogens. The thermal maturity increases to the east of the studied area. The organic matter is within the dry gas zone in the eastern part of the study area and is mature and immature in both the western and northwestern parts of the study area. Various diagrams and relationships between bulk properties and biomarkers help recognize different oil families in Iraqi Kurdistan. Four main oil families are recognized: (1) the Upper Jurassic Taq Taq; (2) the Lower Jurassic Tawke; (3) the Upper Jurassic Kirkuk; and (4) the Tertiary Kirkuk. The geochemical parameters suggest carbonate source deposited in reducing environments for the oils. The biomarker parameters show no evidence of molecular contribution from Sargelu Formation to the oils in Taq Taq, but Tawke and Kirkuk oils show a molecular contribution from Sargelu Formation.

Hydrocarbon migration and accumulation in the Upper Cretaceous Qingshankou Formation, Changling Sag, southern Songliao Basin: Insights from integrated analyses of fluid inclusion, oil source correlation and basin modelling

The Upper Cretaceous Qingshankou Formation acts as both the source and reservoir sequence in the Changling Sag, situated in the southern end of the Songliao Basin, northeast China. An integrated approach involving determination of hydrocarbon charging history, oil source correlation and hydrocarbon generation dynamic modeling was used to investigate hydrocarbon migration processes and further predict the favorable targets of hydrocarbon accumulations in the Qingshankou Formation. The hydrocarbon generation and charge history was investigated using fluid inclusion analysis, in combination with stratigraphic burial and thermal modeling. The source rocks began to generate hydrocarbons at around 82Ma and the hydrocarbon charge event occurred from approximately 78Ma to the end of Cretaceous (65.5Ma) when a large tectonic uplift took place. Correlation of stable carbon isotopes of oils and extracts of source rocks indicates that oil was generated mainly from the first member of Qingshankou Formation (K2qn1), suggesting that hydrocarbon may have migrated vertically. Three dimensional (3D) petroleum system modeling was used to evaluate the processes of secondary hydrocarbon migration in the Qingshankou Formation since the latest Cretaceous. During the Late Cretaceous, hydrocarbon, mainly originated from the Qianan depression, migrated laterally to adjacent structural highs. Subsequent tectonic inversion, defined as the late Yanshan Orogeny, significantly changed hydrocarbon migration patterns, probably causing redistribution of primary hydrocarbon reservoirs. In the Tertiary, the Heidimiao depression was buried much deeper than the Qianan depression and became the main source kitchen. Hydrocarbon migration was primarily controlled by fluid potential and generally migrated from relatively high potential areas to low potential areas. Structural highs and lithologic transitions are potential traps for current oil and gas exploration. Finally, several preferred hydrocarbon accumulation sites have been identified by this work, like Western Slope, Southern uplift, and Eastern Slope, helping reduce the risk on targeting hydrocarbon potential reservoirs in Changling Sag.

The origin of solid bitumen in the Honghuayuan Formation (O1h) of the Majiang paleo-reservoir—Evidence from catalytic hydropyrolysates

Large amounts of solid bitumen occur in the Honghuayuan Formation of the Lower Ordovician (O1h) within the Majiang paleo-reservoir. Most of the potential source rocks and solid bitumens in the Southern Guizhou Depression are of high maturity (%Ro>2). Consequently, the yields of extractable organic matter (EOM) from the potential source rocks and solid bitumens are too low to satisfy the requirement of instrumental analysis. Moreover, the reliability of oil–source correlations based on biomarkers in EOM may be questionable because the routine biomarkers obtained by Soxhlet extraction may have been severely altered by secondary alterations. In this research, catalytic hydropyrolysis (HyPy) is used to release covalently bound biomarkers from highly overmature kerogens and solid bitumens. We analyzed the covalently bound biomarkers and n-alkanes released from the O1h solid bitumens and potential source rock kerogens via catalytic hydropyrolysis by using gas chromatography–mass spectrometry and gas chromatography–isotope ratio mass spectrometry to clarify the oil–source correlation of the Majiang paleo-reservoir. Compared with free biomarkers in EOM, the covalently bound biomarkers released by HyPy exhibit low-maturity characteristics and they retain inherited geochemical information. The oil–source correlation indicates that the Lower Cambrian marine mudstones are the main source for the O1h solid bitumens of the Majiang paleo-reservoir. Furthermore, this research also suggests that some of the O1h solid bitumens had suffered severe biodegradation ahead of thermal alteration.

Lateral Migration of Petroleum in the Jurassic Toutunhe Formation in the Fudong Slope, Junggar Basin, China

AbstractNew oil reservoirs have been discovered recently in the Jurassic Toutunhe Formation in the Fudong slope, Junggar basin in China. The process and mechanism of lateral petroleum migration in the Jurassic System in the Fudong slope was investigated based on the geological analysis of the strata, porosity and permeability of the reservoir rocks and geochemistry on oil–source correlation and oil–oil correlation. The results indicate that hydrocarbons of the Toutunhe Formation were primarily derived from the Middle–Lower Jurassic and Middle Permian source rocks of the western Fukang Depression and migrated along the axis from west to east. The thickness, sand/strata ratio, porosity and permeability of the Toutunhe 2 member are all better than that of the Toutunhe 1 member, making it the main carrier bed of the hydrocarbons lateral migration.