排烃效率对页岩气形成与富集的影响

Effect of hydrocarbon expulsion efficiency on shale gas formation and enrichment

腾格尔 陶成 胡广 申宝剑 马中良 潘安阳 王杰 王向华 徐二社

BORJIGIN Tenger TAO Cheng HU Guang SHEN Baojian MA Zhongliang PAN Anyang WANG Jie WANG Xianghua XU Ershe

中国地质调查局 油气资源调查中心, 北京 100083 中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126 西南石油大学, 成都 610500

Oil and Gas Survey, China Geological Survey, Beijing 100083, China Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China Southwest Petroleum University, Chengdu, Sichuan 610500, China

页岩气富集既需要充足气源，又受后期构造改造强度控制。气源受制于烃源品质和排烃效率，滞留烃量是页岩气生成量的必要条件。通过固体沥青识别和统计，结合氦、碳同位素分析，研究了上奥陶统五峰组-下志留统龙马溪组烃源岩在四川盆地焦石坝、彭水地区的排烃效率、原地生气量及其对页岩气富集的影响。结果表明，五峰组-龙马溪组富有机质层段在焦石坝排烃效率为23%，滞留油量为27.67 kg/t，原地生气量为21.23 m3/t；而在彭水地区的排烃效率为65%，滞留油量为11.0 kg/t，原地生气量为18.99 m3/t，显示差异化生排烃作用，这与印支运动的影响程度有关。4He同位素测年表明，涪陵页岩气开始被封存聚集的时间为231 Ma，处于生油高峰期初期阶段，既气源充足，又利于有机孔隙发育；而彭水页岩气封闭体系形成的起始时间为183 Ma，晚于生气高峰期，气源不足。涪陵页岩气δ13C2为-35.8‰，δ13C1-δ13C2为4.8‰，而彭水页岩气δ13C2为-33.0‰，δ13C1-δ13C2为3.3‰，不同的δ13C分馏效应归因于生烃体系状态的差异性。烃源岩埋藏生烃演化过程中生烃高峰期与关键构造变革期的匹配，最大埋藏期的滞留烃量和抬升剥蚀过程中构造改造强度，联合控制着页岩气的生成、富集和保存。

Shale gas enrichment is not only controlled by sufficient gas source but also by the intensity of later structural transformation.Gas volume is related to source rock quality and hydrocarbon expulsion efficiency, and the amount of shale gas generation depends on remaining hydrocarbon.Based on the identification and statistics of solid bitumen and the analysis of helium and carbon isotopes, the hydrocarbon expulsion efficiency, the in situ gas production of the Upper Ordovician Wufeng and Lower Silurian Longmaxi shales in Jiaoshiba and Pengshui exploration areas and its influence on shale gas enrichment were investigated. The hydrocarbon expulsion efficiency, residual oil volume and in situ gas volume for Jiaoshiba were 23%, 27.67 kg/t and 21.23 m3/t, while those values for Pengshui were 65%, 11.0 kg/t, and 18.99 m3/t, respectively, indicating differential hydrocarbon generation and expulsion related to various influence of the Indosinian Movement.According to the results of 4He isotope dating, Fuling shale gas began to be stored and accumulated at the initial stage (231 Ma) of the oil generation peak period with sufficient gas sources, while the closed system for Pengshui shale gas was formed at the later stage (183 Ma) than the gas generation peak with insufficient gas source. The δ13C2 and δ13C1-δ13C2 for Fuling shale gas were -35.8‰ and 4.8‰, while those values for Pengshui shale gas were -33.0‰ and 3.3‰, respectively.The different δ13C fractionation effects might be attributed to the distinct state of the hydrocarbon generation system. Therefore, the matching of the hydrocarbon generation peak period with the key structural transformation period in the process of hydrocarbon generation and evolution, the hydrocarbon retention amount in the maximum burial period and the structural transformation intensity in the process of uplift and denudation jointly controlled the generation, enrichment and preservation of shale gas.

国家科技重大专项 2017ZX05036-002;国家自然科学基金 41690133

https://doi.org/10.11781/sysydz202003325