川南威远地区二叠系茅口组一段泥灰岩储层特征及其发育主控因素

Characteristics and main controlling factors of the marlstone reservoirs of the first member of Permian Maokou Formatin in Weiyuan area,southern Sichuan Basin

四川盆地南部威远地区的二叠系茅口组一段(下文简称茅一段)勘探程度较低,根据早期的钻井资料所进行的铸体薄片和氩离子电镜分析认为,滑石孔缝为最主要储集空间,滑石化作用对储层贡献最大。而最新钻井实物资料显示,茅一段泥灰岩储层的储集空间类型及储层成因与前期的认识有较大偏差,因此,需要进一步明确该区茅一段泥灰岩储层发育主控因素。通过岩心观察、薄片鉴定、物性分析、氮气吸附—脱附、氩离子抛光扫描电镜和孔隙定量表征,从定性和定量的角度剖析了茅一段泥灰岩主要储集空间和储层类型,结合总有机碳(TOC)含量测定、稀土元素分析以及全岩X衍射等手段,明确了该套储层发育的主控因素。川南威远地区茅一段优质储层发育在泥灰岩中,为一套低孔、低渗裂缝—孔隙型泥灰岩储层,主要发育Ⅲ类储层,少量为Ⅱ类储层;储集空间以溶蚀孔、有机质孔和滑石孔缝为主,孔隙发育与TOC含量具有较好相关性,滑石化作用、白云岩化作用和硅化作用并未产生明显的次生储集空间,对孔隙贡献不明显;泥灰岩储层受早期溶蚀作用、沉积相和有机质丰度共同控制,早期溶蚀作用是泥灰岩溶蚀孔缝形成的关键,内缓坡浅水环境的高初级生产力和高有机质沉降率为有机质孔形成提供了物质基础。该认识可为盆地内相似油气储层的勘探部署提供理论支撑。

The exploration of the first member of Permian Maokou Formation(Maokou 1)in the Weiyuan area of southern Sichuan Basin has been limited.Previous analyses of cast thin sections and argon ion electron microscopy based on earlier drilling data suggested that talc pores were the primary reservoir spaces,with talc formation signifi⁃cantly contributing to the reservoir.However,the latest drilling data shows substantial differences in the types of reservoir spaces and the genesis of the Maokou 1 marlstone reservoirs compared to earlier understanding.It is necessary to further clarify the main controlling factors for the development of these reservoirs in the Maokou 1 member.Through core observation,thin section identification,physical property analysis,nitrogen adsorption,argon ion polishing scanning electron microscopy,and quantitative pore characterization,the primary reservoir spaces and types of the Maokou 1 marlstone were analyzed from both qualitative and quantitative perspectives.The main controlling factors for the development of these reservoirs were identified by combining total organic carbon(TOC)content determination,rare earth element analysis,and whole rock X⁃ray diffraction.High⁃quality reser⁃voirs in the Maokou 1 member of the Weiyuan area are developed in marlstone,characterized by low porosity and permeability fractures and pore⁃type reservoirs,predominantly TypeⅢwith some TypeⅡreservoirs.The main reservoir spaces include corroded pores,organic matter pores,and talc pores and fractures,with pore develop⁃ment closely related to TOC content.Talc formation,dolomitization,and silicification did not significantly contribute to secondary reservoir spaces,and their contribution to porosity is minimal.The development of marlstone reservoirs is jointly controlled by early dissolution,sedimentary facies,and organic matter abundance.Early dissolution is the key to the formation of corroded pores and fractures,while high primary productivity and high organic matter settling rate of the inner gentle slope shallow water environment provided the material basis for the formation of organic matter pores.This understanding provides theoretical support for the exploration of similar oil and gas reservoirs in the basin.