Evidence of the Middle Permian marine mixed type source rocks in the northwestern Sichuan Basin and its contribution to large gas reservoirs in Shuangyushi area
Gao Guohui1, Cao Jian1, Luo Bing2, Xiao Di1, Zhang Ya2, Chen Cong2
1. School of Earth Sciences and Engineering, Nanjing University, Jiangsu Nanjing 210023, China;
2. Research Institute of Exploration and Development, PetroChina Southwest Oil and Gas Field Company, Sichuan Chengdu 610000, China
Gas exploration has made a major breakthrough in Permian Qixia Formation of the Shuangyushi structural belt in the northwest of Sichuan basin, revealing a new exploration field. However, the geochemical characteristics of gas are not in line with the typical characteristics of oil cracking gas from the Cambrian Qiongzhusi Formation as expected. To explain this contradiction, the paper conducts a study through the geological survey of field sections and analysis of downhole core samples in combination with the geological background. The research results show that the marine mixed marls in Middle Permian Qixia Formation and Maokou Formation may be regional effective source rocks. These two sets of source rocks are widely distributed in the northwestern Sichuan Basin, with thicknesses of 0-30 m and 30-150 m, respectively. The source rocks were formed in a marine reducing environment with low salinity. The organic carbon content is 0.86%-7.15%, and the type II organic matter type is dominant. At present, the thermal evolution is mainly in the over mature stage. The equivalent vitrinite reflectance of laser Raman spectroscopy is 1.94%-3.39%. Generally, they are medium-high quality source rocks with good hydrocarbon generation potential, and as the major source rocks, have made substantial contributions to the development of large gas reservoirs in Qixia Formation of the Shuangyushi structural belt. The connectivity between faults and underlying hydrocarbon sources is the key factor determining the differences between Cambrian and Permian hydrocarbon sources. The stable maintenance of traps and good preservation conditions of oil and gas are the key to natural gas accumulation on a large scale.
高国辉, 曹剑, 罗冰, 肖笛, 张亚, 陈聪. 四川盆地西北部中二叠统海相混合型烃源岩的证据及对双鱼石大气藏的成藏贡献[J]. 石油学报, 2020, 41(4): 433-445.
Gao Guohui, Cao Jian, Luo Bing, Xiao Di, Zhang Ya, Chen Cong. Evidence of the Middle Permian marine mixed type source rocks in the northwestern Sichuan Basin and its contribution to large gas reservoirs in Shuangyushi area[J]. Acta Petrolei Sinica, 2020, 41(4): 433-445.
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