川东南地区二叠系—三叠系碳酸盐岩气藏气源及成因类型

Gas source and genetic types of Permian-Triassic carbonate gas reservoirs in Southeast Sichuan

潘磊,秦华,张文睿,李炳弢

PAN Lei, QIN Hua, ZHANG Wenrui, LI Bingtao

中国石化勘探分公司研究院，四川 成都 610041

Research Institute of SINOPEC Exploration Company, Chengdu 610041, China

通过分析天然气组分、碳、氢同位素组成、储层薄片、包裹体等资料，结合烃源岩沉积背景，与邻区对比分析，研究了川东南地区长兴组、飞仙关组、茅口组气藏气源及成因类型。结果表明：飞仙关组、长兴组烷烃气体积分数为51.35%~85.98%，平均74.79%，茅三段烷烃气体积分数为46.71%~99.31%，平均81.68%，均为干气；飞仙关组气藏的甲烷碳同位素值（δ13C1）较轻，平均-34.7‰，长兴组和茅三段岩溶缝洞气藏的δ13C1较重，平均-31.0‰；非烃气以CO2和H2S为主。飞仙关组及部分长兴组储层中见少量沥青，次生矿物中含烃包裹体主要为含气态烃包裹体与气液（水）两相包裹体，未见含油包裹体，与其伴生的盐水包裹体均一温度多高于160 ℃。研究认为，川东南涪陵地区主要为吴家坪组油型气（个别井混有龙马溪组气），以干酪根裂解气为主（飞仙关组和部分长兴组混有少量原油裂解气），綦江地区为龙潭组煤型气。非烃气中H2S来自硫酸盐热化学还原（TSR）反应，CO2来自TSR反应及储层改造时的酸岩反应。

The source gas and genetic types of natural gas in Changxing Formation, Feixianguan Formation and Maokou Formation in Southeast Sichuan are studied through the data of natural gas composition, rock thin section, inclusion and hydrocarbon isotopic composition, combined with the sedimentary background of source rock and comparative analysis with adjacent areas. The results show that alkane gas in Changxing Formation and Feixianguan Formation account for 51.35%￣85.98% with an average of 74.79%, and alkane gas in the third Member of Maokou Formation account for 46.71%￣99.31% with an average of 81.68%, which are all dry gas. Carbon isotope (δ13C1) of methane in Feixianguan Formation is lighter with an average of -34.7‰, that of methane in Changxing Formation and the third Member of Maokou Formation is heavier with an average of -31.0‰. Non hydrocarbons are mainly CO2 and H2S. Only a small amount of asphalt is found in Feixianguan Formation and some Changxing Formation reservoirs. Hydrocarbon inclusions in secondary mineral are mainly gaseous hydrocarbon and gas-liquid (water). No oil-bearing inclusions are found. The homogenization temperature of associated brine inclusions is mostly higher than 160 ℃. The gas type in Fuling area of Southeast Sichuan is mainly oil-based gas of Wujiaping Formation (only some wells are mixed with Longmaxi Formation gas) , and which is mainly kerogen cracked gas (only Feixianguan Formation and some Changxing Formation are mixed with a small amount of crude oil cracked gas) , and gas type in Qijiang area is coal-based gas of Longtan Formation. H2S in non hydrocarbon comes from thermochemical sulfate reduction (TSR) reaction, and CO2 is produced by TSR reaction and acid rock reaction when reservior stimulation.

10.6056/dkyqt202202018