摘要
近年来,四川盆地二叠系茅口组一段不断取得天然气发现,其泥灰岩的储集空间成因机制已成为关注的问题之一。厘米级缝洞型储集空间是茅口组一段新发现的储集空间类型之一,相关研究尚未公开报道。以四川盆地A1井为例,在岩心观察描述基础上,通过显微岩石学、碳氧同位素、锶同位素与微量元素的对比分析,研究了缝洞充填物特征及成因。茅口组一段缝洞中方解石胶结物与泥灰岩基质具有相似的碳氧同位素与锶同位素分布特征,表明方解石主要来源于围岩的溶解再沉淀;与泥灰岩相比,缝洞方解石胶结物的变价元素(V、Cr、U、Mo)、稀土元素(REE)含量降低,而微营养元素(Ni、Cu、Zn)含量升高,揭示了在此过程中微量元素的差异性迁移规律;方解石与泥灰岩基质的Mn与Sr含量的差异性变化特征揭示了成岩流体的海水亲缘属性,进一步表明其与大气淡水、深部热液流体无关。晚侏罗世以来的侧向构造推覆挤压力,形成了川东南地区滑脱断层及相关褶皱体系,在此过程中可能导致了茅口组泥灰岩变形并产生了厘米级裂缝空间。泥灰岩在后续压实—压溶作用(包括侧向压溶)等形成的成岩流体为缝洞石英和方解石胶结物提供了物质来源。
In recent years,natural gas discoveries have been continuously made in the first member of the Permian Maokou Formation in the Sichuan Basin,bringing attention to the genesis mechanism of marlstone reservoir space.Centimeter-scale fracture-cavity type reservoir space is one of the newly discovered types in the first member of the Maokou Formation,and relevant research has not been publicly reported.Taking well A1 in the Sichuan Basin as an example,based on core observation and description,the characteristics and genesis of fracture-cavity fillings were studied through comparative analysis of microscopic petrology,carbon-oxygen isotopes,strontium isotopes,and trace elements.The similar distribution characteristics of carbon-oxygen isotopes and strontium isotopes between calcite cement and mudstone matrix in the fractures of the first member of the Maokou Formation indicated that calcite mainly came from the dissolution and redeposition of surrounding rocks.Compared with marlstone,the fracture calcite cement showed lower contents of valence elements(V,Cr,U,Mo)and rare earth elements(REE),while the content of micronutrient elements(Ni,Cu,Zn)increased,revealing the differential migration pattern of trace elements in this process.The differential variation characteristics of Mn and Sr contents between calcite and marl matrix revealed the marine affinity of diagenetic fluids,further indicating their independence from atmospheric freshwater and deep hydrothermal fluids.Since the Late Jurassic,lateral tectonic thrusting pres-sure has formed detachment faults and related fold systems in southeastern Sichuan,which potentially caused deformation of the Maokou Formation marlstone and the generation of centimeter-scale fracture spaces.Diagenetic fluids formed during subsequent compaction-dissolution processes(including lateral dissolution)provided material sources for quartz and calcite cement in the fractures.
作者
孟宪武
尤东华
李蓉
宋晓波
张力钰
朱兰
MENG Xianwu;YOU Donghua;LI Rong;SONG Xiaobo;ZHANG Liyu;ZHU Lan(Research Institute of Exploration and Development,SINOPEC Southwest Oil and Gas Company,Chengdu,Sichuan 610041,China;Wuxi Research Institute of Petroleum Geology,SINOPEC,Wuxi,Jiangsu 214126,China)
出处
《石油实验地质》
CAS
CSCD
北大核心
2024年第3期483-490,共8页
Petroleum Geology & Experiment
基金
国家自然科学基金项目(U19B6003)
中国石化西南油气分公司科技攻关项目(KJ-632-2102)联合资助。
