Nano Pore Characteristics Of Deep Shale And Its Influence On Reservoir Physical Properties

With the increasingly mature exploration and development technology of medium and shallow shale gas,China’s shale gas exploitation will inevitably transfer to the deeper layer with more abundant shale gas resources.Clarifying the pore characteristics of deep shale and their impact on physical properties is the premise and basis for accurately selecting dessert distribution,predicting deep shale gas production and reasonably planning shale gas exploration and development.In this paper,the deep shale of Wufeng Formation Longmaxi Formation in Jingmen exploration area is taken as the main research object.Based on the systematic collection and summary of regional geological data,the organic geochemical characteristics such as the abundance,maturity and type of organic matter are analyzed.The mineral composition information and shale physical property parameters are obtained through X-ray diffraction,helium hole method,pulse attenuation method and pressure attenuation method.Nanometer CT,focused ion beam scanning electron microscopy and CO₂ adsorption are used The method of low temperature liquid nitrogen adsorption and high pressure mercury injection combined testing qualitatively and quantitatively characterized the shale pores,obtained the full pore size characterization of shale pores,preliminarily revealed the development mechanism of deep shale nano pores and its main controlling factors,and found out the relationship between pore characteristics and reservoir physical properties.The research results show that the deep shale lithology of Wufeng Formation Longmaxi Formation in Jingmen exploration area is mainly black shale,silty shale and carbonaceous shale;The shale minerals are mainly siliceous minerals and clay minerals,and the illite content in clay minerals is the largest,and the illite content increases with the depth;The average organic carbon content is 3.09%,which belongs to high-quality shale.The kerogen type is mainly typeⅡ2,and the average maturity of organic matter is 2.84%,which belongs to the over mature stage;The average porosity of shale reservoir is 1.58%,the average fracture permeability is 0.0058m D,and the average matrix permeability is 0.000052m D.It is an ultra-low permeability reservoir.The correlation between porosity and permeability of shale in the study area is good.The porosity and permeability of shale are affected by TOC,siliceous mineral content,and clay content.Changes in a wide range of depths have a significant impact on shale permeability,but have a small impact on porosity.Shale pores in the study area include organic matter pores,clay mineral interlayer pores,and brittle mineral pores,among which organic matter pores are the most developed,and the overall connectivity of pores is good;Shale has the largest proportion of micropores,which play a major role in pore volume and specific surface area;The contents of TOC and clay minerals respectively affect the pore structure parameters of micropores and macropores of shale in the study area.The content of TOC mainly affects the overall pore development of shale.When the contents of TOC and clay minerals are close,the pore structure parameters of shale are affected by the contents of quartz and illite;The burial depth of shale in the study area has little influence on the overall pore structure.When the depth range is expanded and the burial conditions of shale reservoir are ideal,the depth has obvious influence on the parameters and types of shale pore structure.The porosity of shale in the study area is controlled by the total pore volume of shale.The main occurrence states of shale gas are free and adsorbed.The pore volume is the control factor of the total gas content and free gas content of shale,and the specific surface area of pore is the control factor of the adsorbed gas content;The permeability of shale in the study area is mainly controlled by the volume of shale macropore and macropore,and macropore and macropore play a major role in the permeability of deep shale in Jingmen exploration area;The seepage of deep shale gas is affected by multi-scale effect.The main flow patterns of shale in the study area are slippage flow and transition flow.The slippage effect of gas is widespread and can enhance the seepage capacity of pores;When other conditions are consistent,the main controlling factors of shale seepage are shale pore diameter and specific surface area.The paper has 41 diagrams,12 tables,and 101 references.