A Study On The Pore Characteristic And Pore Evolution Of Shale Reservoir Of Chang 7 Member Of The Yanchang Formation In Yan An Area

The study of pore characteristics and pore evolution law of shale reservoir can provide the basic geological basis for exploring and discussing the reservoir performance of shale reservoirs,shale gas occurrence processes and mechanisms,and predicting favorable blocks.Therefore,accurately characterizing the pore structure characteristics of shale reservoirs and judging their evolutionary processes in the diagenetic process have become an essential problem in reservoir research.However,the study of pore system characterization and evolution of shale reservoir is currently very weak and still in the process of exploration.The shale of Chang 7 member of the Yanchang Formation of the Upper Triassic in the Ordos Basin is not only a high-quality in the basin source rock but also a favorable shale gas reservoir.On the basis of fully researching and summarizing the research results of domestic and foreign scholars,this paper aims at the Chang 7 continental shale in Yanan area of Ordos Basin and uses logging data to study the distribution of continental shale.By means of gas adsorption,field emission scanning electron microscope,X-ray diffraction,vitrinite reflectance measurement and rock pyrolysis and other testing methods,the mineralogical and organic geochemical characteristics of Chang 7 continental shale were systematically studied,and the diagenetic stages of continental shale and the pore types and pore structure characteristics were determined,the pore evolution rules of continental shale were summarized and the main factors influencing the development and evolution of shale pores were discussed.The results show that: the continental shale mineral composition is complex and varied,rich in clay minerals,quartz and feldspar,and contains a small amount of carbonate;organic matter content is distributed in the range of 0.3%-9%,mainly distributed in 3%-6%,the vitrinite reflectance of kerogen type II kerogen as the main organic matter is mainly concentrated in between 0.7%-1.0%.Chang 7 continental shale has underwent compaction,cementation,dissolution,mineral transformation and organic matter thermal evolution and hydrocarbon generation transformation have been jointly reformed,and has generally entered the middle diagenesis A stage.There are various pore types in Chang 7 continental shale,including intergranular pore,intragranular pore,intergranular pore,organic pore and fracturepore,among which intergranular pore and intergranular pore are the most important pore types,and organic matter pore and intragranular pore are relatively undeveloped.The pore morphology is complex,the whole is wedge-shaped and plate-shaped slit,and the micropores are mostly disconnected pores.The pore size distribution is wide(0.1nm-10000nm),the porosity is 0.7%-5%,the mesoporous(2-50nm)and macropores(> 50nm)are the main contributors to the porosity.Diagenesis,lithofacies type and thermal evolution of organic matter are the main factors that influence the pore development and evolution of Chang 7continental shale.