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

Ji, Liming; Cong, He; Zhang, Mingzhen; Wu, Yuandong; Li, Xiangbo

doi:10.1016/j.marpetgeo.2016.02.021

Cited by 31 publications

(16 citation statements)

References 44 publications

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“…Although likely affected by the composition of the source rocks, the ratios of the drimane series compounds from different source rocks are different. Therefore, oil source analyses in the Ordos Basin commonly use the relative abundance of C 30 ‐diahopane and drimane series compounds to classify the source rocks and the crude oils types (Deng, Zhang, Bao et al, ; Deng, Zhang, Wang et al, ; Ji, He, Zhang, Wu, & Li, ; Yang, et al, ).…”

Section: Discussionmentioning

confidence: 99%

Migration and accumulation of crude oil in Upper Triassic tight sand reservoirs on the southwest margin of Ordos Basin, Central China: A case study of the Honghe Oilfield

et al. 2017

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The Upper Triassic tight sand oil in the Ordos Basin has gradually become a focus of research; however, compared to the centre of the basin, studies on the margin have been relatively weak. In this study, an integrated approach involving oil–source correlation, charge history, and pressure evolution is used to investigate the migration characteristics of each stage and to establish a migration and accumulation process model of the tight sand oil in the Yanchang Formation of Honghe Oilfield in combination with reservoir densification process. The results show that, based on the fluid inclusion analysis and authigenic illite K–Ar dating technique in combination with burial and thermal modellings, the accumulation periods were 145–130, 120–90, and 90–80 Ma, which corresponds to the Cretaceous. According to the relative content of C30‐diahopane and drimane series compounds, the crude oil from Chang 8(T3ch8) and Chang 9(T3ch9) both originated from the oil shale of Chang 7(T3ch7) in the Upper Triassic Yanchang Formation. The migration characteristics and directions are comprehensively analyzed using the maturity parameters and key elements. In the early stage of the Early Cretaceous, with east‐dipping strata, crude oil migrated from northeast to southwest. During the late Early Cretaceous, the middle‐late Yanshanian movement promoted the development of strike‐slip faults and fractures, and the oil migrated vertically downwards along them. Tectonic inversion changed the strata dip direction to west‐dipping, and lateral migration was also changed to two directions of southwest and northeast. After the Late Cretaceous, the migration dynamics weakened due to strata uplift and cessation of hydrocarbon generation. Only slight adjustments to the crude oil occurred during the Himalayan movement; therefore, the current distribution pattern of the tight sand oil is still affected primarily by the stage of late Early Cretaceous. The migration and accumulation model of the Upper Triassic in the Honghe Oilfield, Ordos Basin, provides a theoretical basis for further exploration and is of general applicability to tight sand reservoirs in the margins of various basins.

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Section: Discussionmentioning

confidence: 99%

Migration and accumulation of crude oil in Upper Triassic tight sand reservoirs on the southwest margin of Ordos Basin, Central China: A case study of the Honghe Oilfield

et al. 2017

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“…Important breakthroughs have been made in the exploration and development of the crude oil in the Ordos Basin and good achievements have been gained in the geochemical study of Mesozoic crude oil [ 2 – 7 ]. However, because of the scattered geochemical study and uneven distribution of the oil groups of source rock samples [ 8 – 11 ], a systematic study on the geochemistry with abundant samples of crude oil and source rock distributed reasonably in Yanchang Formations is necessary.…”

Section: Introductionmentioning

confidence: 99%

Geochemical Characteristics and Origins of the Crude Oil of Triassic Yanchang Formation in Southwestern Yishan Slope, Ordos Basin

Zhang

Zhao

et al. 2017

International Journal of Analytical Chemistry

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Biomarker compounds that derived from early living organisms play an important role in oil and gas geochemistry and exploration since they can record the diagenetic evolution of the parent materials of crude oil and reflect the organic geochemical characteristics of crude oil and source rocks. To offer scientific basis for oil exploration and exploitation for study area, gas chromatography-mass spectrometry method is applied to study the biomarker compounds of crude oil in Southwestern Yishan Slope of Ordos Basin, through qualitatively and quantitatively analyzing separated materials. The crude oil of Yanchang Formation and the source rocks of Yan'an and Yanchang Formation were collected in order to systematically analyze the characteristics of the biomarker compounds in saturated hydrocarbon fractions and clarify the organic geochemical characteristics of crude oil. The distribution and composition of various types of hydrocarbon biomarker compounds in crude oil suggest that the parent materials of crude oil are composed of hydrobiont and terrigenous plants, and the crude oil is mature oil which is formed in the weak reducing fresh water environment. Oil source correlation results show that the crude oil of Yanchang Formation in Yishan Slope is sourced from the source rocks of Chang 7 subformation.

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“…In 1983, the Triassic Ansai oil field was discovered, and since then, more and more oil fields have been found in Triassic strata (Li and Lu, 2002). Over the past decades, the discovery of a series of oil accumulations in stratigraphic traps of the Yanchang Formation has made the Triassic the most important and prolific petroleum play in the Ordos Basin (Jia and Chi, 2004;Zou et al, 2009;Ji et al, 2016). Many scholars have selected Yanchang organicrich lacustrine mudstones (Chang 7 Shale) as the effective source rocks for the Triassic petroleum play (Zhai, 1997;Hanson et al, 2007;Ji et al, 2007;Duan et al, 2008;Yu et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

“…These oils are predominated by long-chain n-alkanes, abundant C 29 steranes related to C 27 and C 28 homologs, as well as tetracyclic and bicyclic terpanes (Hanson et al, 2007;Duan et al, 2008;Tao et al, 2015). The Chang 7 Shale has been assigned as a principal source rock for generating the Mesozoic oils in the Ordos Basin as it contains abundant bicyclic alkanes that are traced to the most significant biological precursor B. braunii (Ji et al, 2007(Ji et al, , 2016. In order to better understand the sedimentation of the source rock, and the stack pattern of stratigraphic combination, Liu and Yang (2000) deciphered the sequence stratigraphy of the Upper Triassic -Jurassic sedimentary package based on three unconformity-bounded basin phases.…”

Section: Introductionmentioning

confidence: 99%

Statistical analysis as a tool for assisting geochemical interpretation of the Upper Triassic Yanchang Formation, Ordos Basin, Central China

Pan

Horsfield

Zou

et al. 2017

International Journal of Coal Geology

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The Yanchang Formation in the Ordos Basin is the most important petroleum play not only for conventional oil and gas accumulations, but also for newly emerging shale oil and tight gas resources. The molecular characterization of the basinwide source rocks predicts three groups of generative petroleum types: Paraffinic High Wax Oil, mixed base (Paraffinic-Naphthenic-Aromatic) Low Wax Oil, and Gas and Condensate. Supplementary to previous work, 68 samples including the crude oils, source bitumens and reservoir extracts from the Yanchang petroleum play are analyzed. The distribution of two terpane classes (eight tricyclic terpanes and eight pentacyclic terpanes) are determined with subsequent simultaneous RQ-mode factor analysis for a composite data set of these samples alongside 216 published crude oils worldwide with known facies descriptions. Thermal maturity has been evaluated as a consistent distribution at first using a combined method of a maturity-related biomarker [Ts / (Ts + Tm)] and aromatic parameters (Methyldibenzothiophene Ratios) to alleviate the maturity differences effect when discussing geochemical characterization. The R-mode factor analysis consists of the first two factors that are describing 45 present of the cumulative total variance in the data set, and presents a sample grouping pattern in Q-mode factor analysis which is determined by different contributions of terpane associations, i.e., the tricyclic C 21 coupled with pentacyclic C 26 , C 27 , C 28 and C 30 , in the same factor space. Three terpane associations, the C 26 and C 28 terpanes, the C 21 and C 30 terpanes and the C 27 pentacyclic terpenes, are respectively responsible for discriminating crude oil, reservoir extracts and source bitumens in RQ-mode factor analysis. Molecular compositions further address more detailed interrelationships among three sample groups that crude oils and reservoir extracts are sharing close genetic relationships both in depositional environment typing and C 27 -C 28 -C 29 sterane distribution. Samples from source rocks vary much significantly. A mixing process which occurs after oils has been expelled from host source rocks into carrier units during accumulation. In addition, the migration-contamination of C 29 sterols when oils are cross through the Chang 7-2 unit along migration pathways might also explain this lack of correlation between source rocks and oil-reservoir system.

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

Cited by 31 publications

References 44 publications

Migration and accumulation of crude oil in Upper Triassic tight sand reservoirs on the southwest margin of Ordos Basin, Central China: A case study of the Honghe Oilfield

Migration and accumulation of crude oil in Upper Triassic tight sand reservoirs on the southwest margin of Ordos Basin, Central China: A case study of the Honghe Oilfield

Geochemical Characteristics and Origins of the Crude Oil of Triassic Yanchang Formation in Southwestern Yishan Slope, Ordos Basin

Statistical analysis as a tool for assisting geochemical interpretation of the Upper Triassic Yanchang Formation, Ordos Basin, Central China

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