Comparative Analysis Of Shale Gas Enrichment And Depletion Factors In The Wufeng-longmaxi Formation In The Sichuan Basin And Its Periphery

The Sichuan Basin and the surrounding area are the preferred exploration areas for marine shale gas in China.The Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation are the main exploration targets for shale gas.In this paper,the main factors controlling the shale gas enrichment and depletion of the Wufeng-Longmaxi Formation in the Sichuan Basin and the surrounding area are determined through the study of the material basis,reservoir development conditions and preservation conditions of the shale gas formation in the study area.The samples of this thesis were derived from the core samples of some wells in the Jiaoshiba area,Changning area,Weiyuan area,and the Dazu area of the gas-poor area and the southeastern part of the area.Combined with TOC test,Ro test,micro-component test,XRD full-rock diffraction,low-temperature nitrogen adsorption,low-temperature carbon dioxide adsorption,helium gas porosity measurement,pulse permeability test and other unconventional geochemical experiments and reservoir test analysis.In the experiment,the geochemical parameters and reservoir parameters related to the wells of the Sichuan Basin and the marginal gas-rich wells and the lean gas were tested.The results show that the TOC content in the Wufeng-Longmaxi Formation rich gas zone in the Sichuan Basin and the surrounding area is higher,the TOC of most samples is more than 3%,and the TOC content in the vertical direction reaches the maximum in the lower part of the Longmaxi Formation.The type of organic matter is mainly type I and type II₁kerogen,the degree of thermal evolution is generally higher,and the equivalent vitrinite reflectance is mostly greater than 2.3%.The mineral composition is dominated by quartz and clay minerals.The quartz content in the enrichment zone is generally greater than 40%,and the enrichment zone is significantly more than the quartz content in the depleted zone.In the vertical direction,the quartz content in the bottom of the Longmaxi Formation is the largest.The enrichment zone has good physical properties,high porosity permeability,porosity greater than 4%,and permeability greater than1×10^-3?m².The pore types of the study area are variously developed.Organic pores,intergranular pores,intragranular pores and micro-cracks are generally developed.The pore morphology of the enrichment zone is mostly H4 type,and the specific surface area and pore volume are mostly provided by micropores and mesopores.The pore volume is mostly around 0.02 cm ³/g,and the specific surface area is more than 20 m²/g.The late stage of the enrichment area is late and weak.The pressure coefficient is high,mostly around 2,the high angle cracks are relatively undeveloped,the top and bottom plates are in good condition,and the top and bottom plates are thick.In summary,through the comparative analysis of the angry elements,gas storage elements and preservation factors in the enrichment area and the depleted area,the conclusions are drawn.?1?The organic matter has high abundance,good type,moderate degree of organic matter thermal evolution,and is Wufeng-Longmaxi Formation.Key gas production factors for shale gas enrichment.?2?Rich in brittle minerals,good physical properties,high specific surface area and pore volume,and abundant micro-cracks are the key reservoir elements for the shale gas enrichment of the Wufeng-Longmaxi Formation.?3?The structural preservation time is late,the strength is low,the pressure coefficient is high,the high angle crack is not developed,and the top and bottom plate conditions are good.The key preservation factors of the Wufeng-Longmaxi group shale gas enrichment.?4?The matching of the gas conditions,reservoir conditions and storage conditions of the Wufeng-Longmaxi Formation in the Sichuan Basin and the surrounding margin controls the enrichment and depletion of shale gas.