The Characteristics And Influence Of Pore Structure On Gas Content Of The Wufeng-Longmaxi Formation Shale In Southern Sichuan Basin

Shale pores are the main reservoir space of shale gas.The pore structure characteristics control the gas content of shale.In this thesis,the shale core samples of Wufeng-Longmaxi Formation in Southern Sichuan Basin were taken as the research object.The pore structure of shale was characterized by experiments of FE-SEM,high pressure mercury injection,low temperature N₂ adsorption and CO₂ adsorption.The gas content of shale was measured by CH₄ isothermal adsorption experiment,and the influence of pore structure of shale on gas content was analyzed.The results show that the average TOC content of Wufeng-Longmaxi Formation shale in Southern Sichuan Basin is 2.71%.The types of organic matter are mainly type?and type?₁,where type?dominates.The average Ro is 2.82%,belonging to the stage of high maturation to over maturation.The main minerals of shale are clay minerals,quartz and carbonate rocks,with an average content of 38.97%,35.12%and 18.56%,respectively.Feldspar and pyrite are rare.There are 4 types of shale pores in the study area,including organic pores,intragranular pores,intergranular pores,and micro-fracture.Macropores,mesopores and micropores account for 18.46%,55.28%and 26.26%of the total pore volume,which is mainly contributed by pore sizes of 0.3?0.6nm,2?6nm,10?20nm,100?1000nm and 5?10?m.Macropores,mesopores and micropores account for 0.14%,31.47%and 68.39%of the total surface area,which is mainly contributed by pores with pore diameters of 0.3?0.4nm,0.45?1.6nm,2?6nm and 50?100nm.Mesopores provide the main pore volume and micropores provide the main surface area.The average fractal dimension of macropores is 2.8248,and the average fractal dimension of mesoporous pores is 2.8797,indicating that the pore structure of shale is complex and highly heterogeneous.The average maximum adsorption capacity of shale in the study area is1.8062mg/g.The pore volume and surface area provided by micropores and mesopores are the main factors affecting shale gas content,while macropores and the heterogeneity of pore structure has no obvious correlation with shale gas content.