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Origin of conventional and shale gas in Sinian-lower Paleozoic strata in the Sichuan Basin; relayed gas generation from liquid hydrocarbon cracking

Zhao Wenzhi, Zhang Shuichang, He Kun, Hongliu Zeng, Hu Guoyi, Zhang Bin, Wang Zhaoyun and Li Yongxin
Origin of conventional and shale gas in Sinian-lower Paleozoic strata in the Sichuan Basin; relayed gas generation from liquid hydrocarbon cracking
AAPG Bulletin (June 2019) 103 (6): 1265-1296

Abstract

Large amounts of natural gas have been discovered recently, both in carbonate reservoirs and in shales in the Sinian-Silurian strata of the Sichuan Basin, southern China. Although numerous studies have been conducted to learn about the accumulation of conventional and shale gas, the gas generation history, the origins of the two types of gas, and gas resources in the basin remain unclear. In this study, the hydrocarbon generation histories of Cambrian and Silurian source rocks were reconstructed on the basis of thermal history and hydrocarbon generation kinetic parameters. Intensive cracking of crude oil to generate considerable amounts of secondary cracking gas in Silurian and Cambrian formations occurred during deep burial. The high abundance of overmature pyrobitumen in carbonate reservoirs and shale demonstrates the occurrence of large-scale in situ cracking of liquid hydrocarbons. A mixing model was proposed to quantitatively determine the contribution of kerogen and oil-cracking gas in shale gas accumulations. The mixing of two thermogenic gases with different maturities resulted in a reversal and a rollover of the carbon isotope compositions of shale gas. Moreover, gas resources from the cracking of three occurrence states of liquid hydrocarbons--including dispersed residual bitumen in source rocks, dispersed oil outside the source, and accumulated oil in reservoirs--were evaluated in Sinian-Cambrian and Silurian petroleum systems in the Sichuan Basin, providing a guide for future deep gas exploration of similar formations in China and elsewhere.


ISSN: 0149-1423
EISSN: 1558-9153
Coden: AABUD2
Serial Title: AAPG Bulletin
Serial Volume: 103
Serial Issue: 6
Title: Origin of conventional and shale gas in Sinian-lower Paleozoic strata in the Sichuan Basin; relayed gas generation from liquid hydrocarbon cracking
Affiliation: PetroChina, Research Institute of Petroleum Exploration and Development, Beijing, China
Pages: 1265-1296
Published: 20190615
Text Language: English
Publisher: American Association of Petroleum Geologists, Tulsa, OK, United States
References: 87
Accession Number: 2019-062095
Categories: Economic geology, geology of energy sources
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sects., strat. col., 1 table, geol. sketch maps
N31°00'00" - N36°00'00", E103°00'00" - E109°00'00"
Secondary Affiliation: University of Texas at Austin, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by American Association of Petroleum Geologists, Tulsa, OK, United States
Update Code: 201932
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