四川盆地北部灯影组四段台内地区油气来源及成藏过程

Hydrocarbon sources and accumulation processes in intra-platform of the fourth member of Dengying Formation in northern Sichuan Basin

杨毅 朱祥 张雷 徐祖新 代林呈

YANG Yi ZHU Xiang ZHANG Lei XU Zuxin DAI Lincheng

1. 深层油气全国重点实验室, 成都 610041; 2. 中国石化 勘探分公司, 成都 610041

1. State Key Laboratory of Deep Oil and Gas, Chengdu, Sichuan 610041, China; 2. SINOPEC Exploration Company, Chengdu, Sichuan 610041, China

四川盆地上震旦统灯影组四段台内地区是天然气勘探的重要接替领域。为落实川北灯四段台内地区油气成藏富集规律及分布特征，基于台内和台缘地区天然气和沥青地球化学特征、薄片鉴定以及流体包裹体等分析化验资料，开展了川北灯四段台内地区油气来源与成藏过程研究。研究表明：(1)与台缘地区相比，川北灯四段台内地区具有储层沥青碳同位素重，天然气甲烷、乙烷碳同位素重，甲烷氢同位素轻的特征，说明台内地区油气主要来源于筇竹寺组和震旦系烃源岩的混源，且震旦系烃源岩贡献较大；(2)川北灯四段台内地区油气藏存在2期油充注和2期天然气充注，第一期低熟油充注发生在加里东晚期，第二期规模原油充注发生在晚二叠世—中三叠世，第三期原油裂解气充注发生在中侏罗世—晚侏罗世，第四期天然气调整充注发生在白垩纪；(3)通南巴地区从油藏期到气藏期长期处于古构造低部位，古油气藏原油和天然气持续向米仓山前高部位调整运移，导致通南巴地区古气藏调整散失，现今含气性较差。南江地区源储配置关系好，在主要生油生气期均处于古构造高部位，能持续接受天然气充注，且断层封闭性好，有利于气藏保存与油气富集，是川北灯四段台内地区下一步有利勘探区。

The intra-platform of the fourth member of the Dengying Formation in the Upper Sinian of the Sichuan Basin is an important area for gas exploration. To clarify the hydrocarbon accumulation and enrichment patterns and distribution characteristics in this region, a study was conducted on the hydrocarbon sources and accumulation processes based on geochemical characteristics of natural gas and bitumen, thin-section observation, and fluid inclusion analysis of the intra-platform and platform margin areas. The results indicated that: (1) Compared to the platform margin areas in the fourth member of the Dengying Formation in northern Sichuan Basin, the intra-platform exhibited higher amounts of carbon isotopes in bitumen and natural gas methane and ethane, with smaller amounts of isotopes in hydrogen. This indicated that the oil and gas in the intra-platform mainly originated from a mixed source of the Qiongzhusi Formation and Sinian hydrocarbon source rocks, with a larger contribution from the Sinian source rocks. (2) There were two phases of oil charging and two phases of natural gas charging in the oil and gas reservoirs in the intra-platform of the fourth member of the Dengying Formation in northern Sichuan Basin. The first phase of low-maturity oil charging occurred in the Late Caledonian, the second phase of large-scale crude oil charging took place from the Late Permian to the Middle Triassic, the third phase involved crude oil pyrolysis gas charging during the Middle to Late Jurassic, and the fourth phase was natural gas adjustment charging in the Cretaceous. (3) The Tongnanba area has long been located in the lower part of the paleostructure from the oil accumulation to the gas accumulation period. The crude oil and natural gas from the paleo-oil and gas reservoirs continuously adjusted and migrated towards a higher position in the front of Micang Mountain, resulting in the loss of paleo-gas reservoirs in the Tongnanba area, which now has relatively poor gas content. The Nanjiang area had a more favorable source and reservoir configuration, remaining in the higher part of the paleostructure during the main oil and gas generation periods. It continuously received natural gas charging, and the fault sealing was good, which was conducive to gas reservoir preservation and oil and gas accumulation. Therefore, the Nanjiang area in the intra-platform is the next favorable exploration zone in the fourth member of the Dengying Formation in northern Sichuan Basin.

深层油气全国重点实验室开放课题(SKLDOG2024-KFYB-04)和中国石化科技部项目(P23221)联合资助。

https://doi.org/10.11781/sysydz2025020384