Research On Pore Structure Characteristics Of Shale In Xiamaling Formation Of Yanshan

The Xiamaling formation of middle-upper Proterozoic developed a set of rich organic mud shale in the Yanshan area,and has good shale gas accumulation conditions.Based on the field geological survey and regional geological data research,combined with the thermal simulation and other testing techniques,the characteristics of the low mature shale,pore structure,pore development and other factors in the Xiamaling formation of Yanshan area are discussed in depth.The shale in the Xiamaling Formation of the northern Hebei area is shallow sedimentary facies,the brittle mineral content is high,the content of organic matter can reach more than 4%;the kerogen type is mainly type I,the part is ? type.The reflectivity of plastids is 0.7%~2.03%,the overall performance is good hydrocarbon generating potential.The various types of pores in the Xiamaling formation is mainly developed,such as dissolution hole,intergranular hole,interlayer hole and micro fracture.The pore structure is complex,the development of water bottle hole,parallel plate hole,open hole and ink bottle hole and other forms of holes.The pores and transition holes have the largest contribution to pore volume and specific surface area,and the pore connectivity is medium or better.The fractal dimension is higher and the fractal dimension is lower,which is beneficial to the adsorption,desorption,seepage and reservoir of gas.Pore structure of pores which size is greater than 100 nm is more complex,the pore surface is not uniform,that is not conducive to gas seepage.The development of shale porosity is affected by sediments,tectonics,mineral composition,diagenesis,thermal evolution and other factors.The shallow-water shelf sediments provide a large amount of organic matter for shale of Xiamaling formation,it also provides sufficient material basis for the development of organic matter pores.The effect of mineral composition on the inorganic pore of shale is obvious,and the effect of brittle mineral is more obvious than that of clay mineral.Diagenesis mainly affects the intergranular pores and cracks.The thermal simulation shows that the total amount of pores increases linearly during the thermal evolution of organic matter,especially the microporous content can be increased to 9.04 times of that in the original state.There is a difference in the degree of influence of the thermal evolution of the pore size in different scale ranges.The micropores and mesopores are increasing with the process of thermal evolution,while the transition pore and macroporosity are increasing first and then decreasing sharply.And the samples of low-middle maturity showed the parallel plate hole,and the pores of each pore size were developed.The pores of the mature sample reflect the morphology of the amorphous pores combined with the qualitative pore,and its pore connectivity is higher than that of low-maturity samples.In the mature stage,the samples mainly develop amorphous pores.Therefore,with the increasing degree of organic matter thermal evolution,pore size distribution gradually concentrated,pore connectivity gradually increased,the paper will be divided into six stages of pore structure evolution.The evolution of the pore structure directly determines the spatial occurrence of shale gas.The adsorption gas increases with the pore size increasing and then gradually increases,and the free gas increases with the increase of the pore size.In general,the adsorption gas and free gas show different increasing rates in different pore diameters.The effect of thermal evolution on the adsorption of gas at different size pores is different.In terms of sensitivity,the macroporous is the most sensitive,the mesopores are the second,and the micropores are the weakest.The contribution of micropores and mesopores to the surface area is the most obvious,and it is also the most favorable for shale gas adsorption.