Molecular geochemical characteristics of gas source rocks from the Upper Triassic Xujiahe Formation indicate transgression events in the Sichuan Basin

The geochemical characteristics of saturated and aromatic hydrocarbons from different formations and lithologies provide ob-vious evidence for transgressions that occurred during Upper Triassic Xujiahe stage in Sichuan Basin with a great impact on the source input and depositional environment.A clear dual peak distribution for normal alkanes and obvious abundant com-pounds sourced from bacteria and algae in whole oil gas chromatogram indicates the abundance of lower organisms input.The ratio of Pr/Ph is low,ranging from 0.33 to 0.86 with an average of 0.60,quite different from Pr/Ph >2.0 for coal measures in swamp environment,representing source rocks from saline lake or marine facies.In the gas source rocks extracts,abundant β-carotane,-carotane,and their degradated series were detected in the whole oil chromatogram,indicating a reducing envi-ronment.The concentrations of methyl steranes and dinosteranes are high.The content of polycyclic aromatic sulfur heterocy-cles(PASH) is relatively higher in aromatic fraction and the assemblage of fluorene,dibenzofuran,and dibenzothiophene is different from the typical saline lake and the regular swamp facies source rocks,manifesting the transgression effects on gas source rocks.

Sinian gas sources and effectiveness of primary gas-bearing system in Sichuan Basin, SW China

Based on correlation between geochemical characteristics of Sinian and Cambrian source rocks and discovered gas reservoirs,paleoand the analysis on geological conditions of reservoir formation,the sources of natural gas in the Sinian of Sichuan Basin have been discussed to sort out the contribution of Sinian source rocks to the gas reservoirs and effectiveness of Sinian primary gas-bearing system.Through the analysis of natural gas composition,carbon and hydrogen isotopes and effectiveness of Sinian accumulation assemblages,it is concluded that:(1)The natural gas derived from the Sinian source rock is characterized by low ethane content,heavy ethane carbon isotope and light methane hydrogen isotope,and obviously different from the gas generated by the Cambrian source rock.(2)The gas reservoirs discovered in Sinian Dengying Formation are sourced by Sinian and Cambrian source rocks,and the Sinian source rock contributes different proportions to the gas in the 4th member and the 2nd member of the Dengying Formation,specifically,39%and 55%to the 4th member in marginal zone and intra-platform,54%and 68%to the 2th member in the marginal zone and intra-platform respectively.(3)The effectiveness of the Sinian primary gas-bearing system depends on the gas generating effectiveness of the source kitchen,reservoir and combination of gas accumulation elements.For high-over mature marine source rocks at the Ro of less than 3.5%,besides gas generated from the thermal cracking of liquid hydrocarbon,the kerogen still has some gas generation potential by thermal degradation.In addition,the Sinian microbial dolomite still preserves relatively good-quality reservoirs despite large burial depths,which match well with other basic conditions for gas accumulation in central Sichuan paleo-uplift,increasing the possibility of Sinian primary gas-bearing system.The research results confirm that the Sinian primary gas-bearing system is likely to form large-scale accumulation.

“Exploring petroleum inside source kitchen”: Shale oil and gas in Sichuan Basin

The Sichuan Basin is rich in shale oil and gas resources,with favorable geological conditions that the other shale reservoirs in China cannot match.Thus,the basin is an ideal option for fully"exploring petroleum inside source kitchen"with respect to onshore shale oil and gas in China.This paper analyzes the characteristics of shale oil and gas resources in the United States and China,and points out that maturity plays an important role in controlling shale oil and gas composition.US shale oil and gas exhibit high proportions of light hydrocarbon and wet gas,whereas Chinese marine and transitional shale gas is mainly dry gas and continental shale oil is generally heavy.A comprehensive geological study of shale oil and gas in the Sichuan Basin reveals findings with respect to the following three aspects.First,there are multiple sets of organic-rich shale reservoirs of three types in the basin,such as the Cambrian Qiongzhusi Formation and Ordovician Wufeng Formation-Silurian Longmaxi Formation marine shale,Permian Longtan Formation transitional shale,Triassic Xujiahe Formation lake-swamp shale,and Jurassic lacustrine shale.Marine shale gas enrichment is mainly controlled by four elements:Deep-water shelf facies,moderate thermal evolution,calcium-rich and silicon-rich rock association,and closed roof/floor.Second,the"sweet section"is generally characterized by high total organic carbon,high gas content,large porosity,high brittle minerals content,high formation pressure,and the presence of lamellation/bedding and natural microfractures.Moreover,the"sweet area"is generally characterized by very thick organic-rich shale,moderate thermal evolution,good preservation conditions,and shallow burial depth,which are exemplified by the shale oil and gas in the Wufeng-Longmaxi Formation,Longtan Formation,and Daanzhai Member of the Ziliujing Formation.Third,the marine,transitional,and continental shale oil and gas resources in the Sichuan Basin account for 50%,25%,and 30%of the respective types of shale oil and gas geological resources in China,with great potential to become the cradle of the shale oil and gas industrial revolution in China.Following the"Conventional Daqing-Oil"(i.e.,the Daqing oilfield in the Songliao Basin)and the"Western Daqing-Oil&Gas"(i.e.,the Changqing oilfield in the Ordos Basin),the Southwest oil and gas field in the Sichuan Basin is expected to be built into a"Sichuan-Chongqing Daqing-Gas"in China.

Theory, Technology and Practice of Unconventional Petroleum Geology

0 INTRODUCTION The breakthroughs in unconventional petroleum have a great impact on world petroleum industry and innovation in petroleum geology(Dou et al,2022;Jia,2017;Zou et al.,2015b,2014a;Yerkin,2012;Pollastro,2007;Schmoker,1995).The exploration and development evolution from conventional petroleum to unconventional petroleum and more and more frequent industrial activities of exploring petroleum inside sources kitchen have deepened theoretical understanding of unconventional petroleum geology and promoted technical research and development(Jia et al.,2021,2017;Jin et al.,2021;Zhao W Z et al.,2020;Ma Y S et al.,2018,2012;Zou et al.,2018b,2016,2009;Dai et al.,2012).We have introduced and extended the theory of continuous hydrocarbon accumulation since 2008 and published several papers/books(in Chinese and English)with respect to unconventional petroleum geology since 2009,basically forming the theoretical framework for this discipline(Yang et al.,2022a,2021a,2019a,,2015a;Zou et al.,2019c,2017b,2014a,,2013a).In this paper,we present the background of unconventional petroleum geology,review the latest theoretical and technological progress in unconventional petroleum geology,introduce relevant thinking and practices in China,and explore the pathway of unconventional petroleum revolution and multi-energy coordinated development in super energy basins,hopefully to promote the unconventional petroleum geology and industry development.