Characteristics Of Inorganic Pores Of The Longmaxi Formation Shale In Southern Sichuan Basin

The southern Sichuan is rich in marine shale gas resources,and is currently the key area for shale gas development.And the Longmaxi Formation shale in southern Sichuan is a key area for research.The characteristics of the Longmaxi Formation shale reservoirs in southern Sichuan have been further studied.Based on this,the research on the micropore structure of the Longmaxi Formation shale reservoirs in southern Sichuan has gradually begun.The study of the structure is difficult to be carried out because it is difficult to distinguish between organic and inorganic by experimental testing methods.Therefore,this article takes the Longmaxi Formation shale samples in the Changning-Weiyuan area of southern Sichuan as the research object.Through literature research,experimental testing,data analysis,and geological conditions and theoretical knowledge,the characteristics of inorganic pore structure and inorganic pores of the Longmaxi Formation shale in southern Sichuan and the evolutionary model are studied.Studies have shown that the classification of inorganic pore types of the Longmaxi Formation shale in southern Sichuan is mainly divided into intergranular pores,brittle mineral edge pores,clay mineral pores,intragranular dissolved pores,pyrite intergranular pores,and microfractures.After quantitative research on the structural characteristics of inorganic pores,it is believed that the marine shale of the Longmaxi Formation in southern Sichuan has low porosity and low permeability,and is rich in micro-nano-level pores,of which macropores and mesopores account for the majority;It is 29.07 nm.Among them,the proportion of macropores larger than 50 nm is 16.4% on average;the proportion of mesopores between 2nm and 50 nm is 77.1% on average;the micropore content is extremely low,and the micropore content in inorganic pores average ratio is 1.6%.At the same time,the influencing factors of the characteristics of inorganic pore structure are discussed.It is considered that the mineral composition and the degree of thermal evolution determined by the original diagenetic environment and the evolution of diagenesis are important factors,and the TOC content may also be the influencing factor affecting the characteristics of inorganic pore structure.Based on experimental data such as scanning electron microscopy and vitrinite reflectance microscopy,the inorganic pore structure was quantitatively analyzed and the evolutionary stages of the inorganic pores were divided.Combined with the diagenesis of various types of reservoirs and the evolution stages of inorganic pores,the evolution pattern of inorganic pores is drawn.It is confirmed that the evolution pattern of the inorganic pores of the Longmaxi Formation shale in south Sichuan corresponds to three stages : The first stage is immature to mid-mature,the reduction in face rate is relatively large,and the macropores above 50 nm in the pore size category have the most reduction,and instead become mesopores,the micropores are not developed;they have a lower aperture aspect ratio and have Increasing trend.The second stage is the maturity-high maturity period,with the most increase in mesopores.The diagenesis is mainly the dissolution of minerals,clay mineral transformation and carbonate recrystallization;the third stage is the overmaturation period,mesopores and micropores.The increase is more obvious,the face rate is generally small,there is a tendency to increase first and then decrease,and the aspect ratio of the pores has a tendency to decrease first and then increase.