南堡凹陷古近系沙河街组一段湖相块状与纹层状页岩储层微观特征差异性研究OA

To investigate the micro-characteristics of laminated lacustrine shale,samples were collected from the first member of the Paleogene Shahejie Formation in the Nanpu Sag.An integrated approach was applied,including nitrogen adsorption,X-ray diffraction,TOC measurement,rock-eval pyrolysis,scanning electron microscopy,and image analysis using ImageJ software.The results show that the shale interval comprises both massive and laminated types,with the latter being dominated by clay,mixed,and felsic laminae.Compared to massive shale,laminated shale exhibits more developed micro-fractures,better pore connectivity,and a higher occurrence of organic matter-filled pores.In contrast,pores in massive shale are smaller and less connected,with organic matter intermittently filling only part of the intergranular pores.Geochemical analysis indicates that laminated shale has higher average TOC(1.06%)and S1 values(1.76 mg/g)than massive shale(TOC:0.60%;S1:0.68 mg/g),confirming its superior oil-bearing potential.The reservoir is dominated by medium-sized pores.While laminated shale has a larger specific surface area and average pore diameter than massive shale,its porosity is relatively lower.Furthermore,as lamina density increases,the porosity of laminated shale increases but TOC content decreases;whereas,with greater variation in grain lamina thickness,porosity decreases and TOC content increases.The laminated mixed shale is a favorable lithofacies for shale oil explora-tion due to its complex pore network,good connectivity and high organic matter abundance.