川中地区营山构造侏罗系自流井组页岩油储层孔隙结构特征及其影响因素OA

This study discusses the characteristics and influencing factors of pore structures for shale oil reservoirs with various lithologies in the Lower Jurassic Ziliujing Formation in the Yingshan structure of central Sichuan Basin.The shale pore structures of the Dongyuemiao and Da'anzhai Members of the Ziliujing Formation were characterized in full scale by means of organic geochemistry,X-ray diffraction(XRD),scanning electron microscopy(SEM),liquid nitrogen adsorption,and high-pressure mercury intrusion.Then,the fractal dimensions of different pore size distributions were calculated based on CO2 adsorption,N2 adsorption,and high-pressure mercury intrusion.Finally,the relationships of fractal dimension with total organic carbon(TOC)content and mineral compositions were discussed,revealing the influences of TOC,clay minerals and brittle minerals on pore structures.The following results are obtained.(i)The mineral compositions of shales in the Dongyuemiao and Da'anzhai Members are dominated by clay minerals and quartzs.The primary lithologies mainly consist of shales and mixed rocks,followed by limestones and siltstones,and the secondary lithologies are mainly composed of silty shales and silty-clayey shales.(ii)Reservoir space development varies with lithology.Silty shales and silty-clayey shales primarily develop clay mineral intergranular pores and grain boundary fractures,with pore size distribution showing a bimodal pattern,peaking mainly at 20-60 nm and＞100 nm.The reservoir spaces in limestones are mainly calcite intergranular pores,calcite intracrystalline pores,and grain boundary fractures,with pore sizes concentrated at 20-60 nm and＜5 nm.(iii)The fractal dimensions of micropores,mesopores and macropores are determined to be 2.480 6-2.988 6,2.338 3-2.554 8,and 2.910 6-2.994 0,respectively,indicating that micropores and mesopores are structurally simple and strongly homogeneous,while macropores are more complex.(iv)TOC promotes micropore formation;clay minerals control mesopore development,homogenizing them in mixed rocks,deteriorating pores in limestones,and stabilizing pore structures in shales;brittle minerals such as quartzs and feldspars form the support skeleton for macropores and overall complexity,but their role in shales requires a specific content threshold;carbonate minerals generally inhibit pore development,and cementation brings the strongest damage to pores in limestones.It is concluded that the pore structures in the Ziliujing Formation shales are controlled by lithology,and strong reservoir heterogeneity is mainly caused by the differentiated control of various mineral compositions on pore structures.