四川盆地不同地区二叠系茅口组缝洞粗晶方解石碳氧同位素差异及其古岩溶环境意义  

Differences of carbon and oxygen isotopes in coarse-grained calcite from the Permian Maokou Formation in different regions of Sichuan Basin and their significance in paleokarst environment

作　　者：高兆龙 淡永 张玺华[1] 曹华 邓敏 陈聪 胡罗嘉 GAO Zhaolong;DAN Yong;ZHANG Xihua;CAO Hua;DENG Min;CHEN Cong;HU Luojia(Research Institute of Petroleum Exploration and Development,Southwest Oil and Gas Field Company,PetroChina,Chengdu,Sichuan 610041,China;Chengdu Center,China Geological Survey,Chengdu,Sichuan 610081,China;Key Laboratory of Sedimentary Basin and Oil and Gas Resources,Ministry of Natural Resources,Chengdu,Sichuan 610081,China)

机构地区：[1]中国石油西南油气田分公司勘探开发研究院,四川成都610041 [2]中国地质调查局成都地质调查中心(西南地质科技创新中心),四川成都610081 [3]自然资源部沉积盆地与油气资源重点实验室,四川成都610081

出　　处：《中国岩溶》2024年第3期684-693,共10页Carsologica Sinica

基　　金：中国石油天然气股份有限公司攻关性应用性科技专项《海相碳酸盐岩油气规模增储上产与勘探开发技术研究》(2023ZZ16)子课题《碳酸盐岩油气富集规律及有利区带研究》;中国石油西南油气田公司科学研究与技术开发项目《四川盆地二叠系规模增储关键问题攻关研究》子课题《四川盆地下二叠统资源潜力与成藏条件研究》(20220301-03);自然资源部深时地理环境重建与应用重点实验室开放基金资助项目(DGERA20231108)共同资助。

摘　　要：茅口组缝洞型储层是四川盆地重要的天然气产层。为认识这些缝洞的形成环境以及在盆地不同地区的差异,通过测试和收集缝洞方解石碳氧同位素数据,发现茅口组方解石碳氧同位素可分为4类,分别指示4种不同流体性质的古岩溶环境:第Ⅰ类缝洞方解石氧同位素值与茅口组灰岩或中二叠海水值基本一致,δ^(13)C为1.8‰~3.83‰,δ^(18)O为-8.95‰~-4.11‰,指示准同生岩溶环境;第Ⅱ类缝洞方解石具有较高负偏的δ^(13)C和δ^(18)O值,δ^(13)C<0‰,δ^(18)O为-12‰~-9‰,指示大气淡水岩溶环境;第Ⅲ类缝洞方解石具有较低的δ^(18)O值,比基岩明显负偏,而δ^(13)C值与基岩值基本一致,δ^(13)C为0‰~3.83‰,δ^(18)O为-12‰~-8.5‰,主要指示埋藏岩溶环境;第Ⅳ类缝洞方解石δ^(18)O值明显偏负(<-12‰),指示高温热液环境。区域对比发现川中、川南较川北氧同位素更负偏,而川北、川中碳同位素较川南更负偏,认为川南地区以埋藏岩溶为主、大气淡水岩溶和准同生岩溶次之,形成以裂缝型为主的储层;川中地区除准同生岩溶、大气淡水岩溶外,还发育有高温热液岩溶,热液岩溶对川中茅口组白云岩中孔洞发育具有贡献;川北地区以准同生岩溶、大气淡水岩溶为主,形成了川北以溶蚀孔洞为主的储层。Oil and gas fields in karst carbonate reservoirs are widely distributed in China.A number of karst fracturevuggy reservoirs have been found in the Tarim Basin,the Ordos Basin and the Sichuan Basin.Therefore,research of reservoirs in karst fractured caves has become one of the focuses in recent years,which indicates a promising future and huge potential for exploring karst carbonate reservoirs in China.Reservoirs in fractured caves of the Maokou Formation have always been one of the key areas for oil and gas exploration in the Sichuan Basin.Since the last century when reservoirs in fractured caves in the southern Sichuan region were discovered,breakthroughs have been made in this field in the Yuanba area of northern Sichuan,Yunjin area of southern Sichuan,and the Penglaiba area of central Sichuan,demonstrating good exploration prospects.However,there has always been controversy over the origin of fractured caves.One view suggests that the exposure of the Maokou Formation caused by the Dongwu Movement and the occurrence of freshwater karst are the main reasons for the development of fractured caves in the Maokou Formation,while another view suggests that fractured caves in the Maokou Formation are related to the tectonic fluid activity during the burial period.these two views are mostly based on research in the southern Sichuan region,and further consideration of the entire Sichuan Basin is needed to search for relevant evidence from geological phenomena to geochemistry.To understand the causes and differences of these fractured caves,we systematically sampled calcite for data of carbon and oxygen isotopes from outcrop profiles or from drilling fractured caves in different areas of the Sichuan Basin,in order to determine the paleokarst environment in which fractured caves were developed.Study results show that fractured caves of the Maokou Formation in this basin are mainly composed of small-and-medium-sized dissolution pores,fractures,and dissolution fractures.The carbon and oxygen isotopes of calcite in the Maoko

关 键 词：四川盆地茅口组 碳氧同位素 古岩溶作用 岩溶储层 热液岩溶 

分 类 号：P618.13[天文地球—矿床学]