川西坳陷中段须家河组四段砂岩中碳酸盐胶结物碳、氧同位素特征及成因探讨  

Carbon and oxygen isotope characteristics and genesis of carbonate cementsin sandstone of the 4th Member of the Xujiahe Formation in the centralwestern Sichuan depression,Sichuan basin,China

作　　者：张庄[1] 庞江 杨映涛[1] 操延辉 戚明辉 张烨毓 张玲 马森 ZHANG Zhuang;PANG Jiang;YANG Yingtao;CAO Yanhuil;QI Minghui;ZHANG Yeyu;ZHANG Ling;MA Sen(Exploration and Production Research Institute of Southwest Branch Com pany,Chengdu,Sichuan 610041,China;Sichuan Key Laboratory of Shale Gas Evaluation and Exploitation,Chengdu,Sichuan 610091,China;Technical Innovation Center for Shale Gas Exploralion and Development in Complex Structural Areas,Ministry of Natural Resources,Chengdu,Sichuan 610091,China;Sichuan Keyuan Testing Center of Engineering Technology,Chengdu,Sichuan 610091,China)

机构地区：[1]中石化西南油气分公司勘探开发研究院,四川成都610041 [2]页岩气评价与开采四川省重点实验室,四川成都610091 [3]自然资源部复杂构造区页岩气勘探开发工程技术创新中心,四川成都610091 [4]四川省科源工程技术测试中心,四川成都610091

出　　处：《地质学报》2022年第6期2094-2106,共13页Acta Geologica Sinica

基　　金：国家科技重大专项(编号2016ZX05002-004-002)资助的成果。

摘　　要：碳酸盐胶结物是川西坳陷须家河组四段砂岩中最常见的成岩矿物。应用激光微区取样碳、氧同位素测试方法,对研究区须四段砂岩中不同类型的碳酸盐胶结物的碳、氧同位素特征进行了精细分析,结合岩相学特征和流体包裹体分析,查明了不同类型碳酸盐胶结物的形成时间和成因机制。研究表明,研究区须四段砂岩中发育Ⅰ、Ⅱ、Ⅲ三期碳酸盐胶结物。第Ⅰ期方解石的δ^(13)C_(PDB)值为-0.13‰~1.53‰,δ^(13)O_(PDB)值为-9.92‰~-6.41‰;第Ⅱ期方解石的δ^(13)C_(PDB)值为-2.44‰~1.85‰,δ^(13)O_(PDB)值为-13.97‰~-10.06‰;第Ⅲ期方解石的δ^(13)C_(PDB)值为-5.34‰~0.75‰,δ^(13)O_(PDB)值为-16.55‰~-14.44‰,第Ⅲ期白云石的δ^(13)C_(PDB)值为-0.97‰~-0.81‰,δ^(13)O_(PDB)值为-13.32‰~-12.91‰。从早期到晚期,碳酸盐胶结物的碳、氧同位素均表现为逐渐变轻,说明其沉淀温度逐渐升高,受有机流体影响逐渐加深。第Ⅰ期碳酸盐胶结物形成于晚三叠世末,储层处于浅埋藏阶段,是从早期过饱和碱性孔隙流体中直接沉淀出来的,其“碳”源主要来自沉积水中溶解的CO_(3)^(2-)。第Ⅱ期碳酸盐胶结物形成于早侏罗世,沉淀温度约45~70℃,其形成有少量有机流体的参与,有机轻“碳”、原始孔隙水中溶解的“碳”以及少量溶蚀作用释放出的重“碳”共同为该期碳酸盐胶结物提供“碳”源。第Ⅲ期碳酸盐胶结物形成于晚侏罗世,沉淀温度约100~140℃,其成因与有机酸性流体关系密切,有机成因的轻“碳”和部分由溶蚀作用释放的重“碳”是该期方解石的主要“碳”源;而该期白云石的沉淀受砂岩中碳酸盐岩岩屑溶蚀的控制更明显,由溶蚀作用产生的重“碳”是其主要“碳”源。Carbonate cements are the most common diagenetic mineral in the sandstone of the 4 th Member of the Xujiahe Formation(T;x~4)in western Sichuan basin.The carbon and oxygen isotopes of different types of carbonate cements were analyzed using laser micro-sampling,in the T;x~4 in the study area.Combined with petrographic characteristics and fluid inclusion analysis,the formation periods and genetic mechanism of different types of carbonate cements have been identified.Carbonate cements developed in the sandstone of T;x~4 in three phases.Theδ^(13)C_(PDB)values of the calcite in PhaseⅠare-0.13‰~1.53‰,while theδ^(13)O_(PDB)values are-9.92‰~-6.41‰.The δ^(13)C_(PDB) values of the calcite in PhaseⅡare-2.44‰~1.85‰,and the δ^(13)O_(PDB) values are-13.97‰~-10.06‰.The δ^(13)C_(PDB) value of the calcite in PhaseⅢis-5.34‰~0.75‰,and the δ^(13)O_(PDB) value is-16.55‰~-14.44‰.The δ^(13)C_(PDB) values of dolomite in PhaseⅢare-0.97‰~-0.81‰,and the δ^(13)O_(PDB) values are-13.32‰~-12.91‰.The carbon and oxygen isotopes of carbonate cements gradually became lighter from early to late,indicating that the precipitation and temperature increased,and the influence of organic fluids becomes stronger.The Phase I carbonate cement formed at the end of the Late Triassic(in the shallow burial stageof the reservoir)was directly precipitated from the supersaturated alkaline pore fluid derived from sedimentary water,and the source of“C”mainly comes from dissolved CO_(3)^(2-)in sedimentary water.The PhaseⅡcarbonate cement precipitated in the Early Jurassic(temperature about 45~70℃).Its formation is slightly affected by organic fluid.Its“C”sources include(1)light“C”from organic fluids,(2)“C”form original pore water,and(3)heavy“C”released by weak dissolution.The PhaseⅢcarbonate cement formed in the Late Jurassic(temperature about 100~140℃),which is closely related to the injection of organic acid fluid.The main“C”sources of the PhaseⅢcalcite are organic light“C”and pa

关 键 词：碳酸盐胶结物 碳、氧同位素 成因机制 须家河组四段 川西坳陷中段 

分 类 号：P618.13[天文地球—矿床学]