The Source And Reservoir Characteristics Of Shale In The Wufeng-Longmaxi Formation And Their Effects On The Shale Sealing Ability In The Southeastern Sichuan Basin

The shale gas is the important resource of the unconventional resources.The Wufeng-Longmaxi Formation shale in the Southeastern Sichuan Basin is the typical marine shale gas favorable formation,and exploration and exploitation have been conducted.Previous researchers studied fault and fissuers effects on shale sealing ability a lot.This paper focuses on hydrocarbon generation and resevior characteristics and their effects on sealing ability of organic matter rich shale,and this research aims at the favorable area for shale gas exploration.This paper is based on geochemistry analysis to clarify the maracels and evolution difference between the Wufeng-Longmaxi formation shale and the Xiamaling shale,and this analysis shows the environments of two shales are similar.Theirfore,this study presents the hydrous pyrolysis plan of Xiamaling formation shale for adding up the Wufeng-Longmaxi formation low maturity stages hydrocarbon generation procedure.This study focuses on pore structures and organic matter thermal maturity of graptolite-bearing shale from the Wufeng-Longmaxi Formation in Sichuan Basin,China.Scanning Electronic Microscope（SEM）and adsorption of gases were used to study the pore structures of residue of samples after hydrous pyrolysis procedure at different temperatures and the Wufeng-Longmaxi formation shale natural samples.During hydrous pyrolysis procedure the Xiamaling formation shale experienced four diagenesis stages,early diagenesis,catagenesis A and catagenesis B,and metagenesis.Bubble-like,shrinking,and internal mineral pores increased drastically in metagenesis.Bitumen was generated into oil during diagenesis and catagenesis.Spongy pores increased the volume of micro-and meso-pores.The Wufeng-Longmaxi formation organic-rich shale pore characteristics and mechanical characteristics are significant to shale gas preservation.Spherical pores were observed in solid bitumen in the samples,while graptolites exhibited porosity.The graptolites pores were evenly distributed and exhibited spindle structures.The solid bitumen pores are primarily in the micropore range（<2nm）,while mesopore（2nm-50nm）and macropore（>50nm）sizes are limited.Methane adsorption of shale is controlled by organic matter micro pore structure.The Transmission electron microscope（TEM）observation of graptolite fragments is good to study the structure of graptolite.Graptolite reflectance（GR_o）and solid bitumen reflectance（BR_o）reflectance index correlated well with each other and with Raman estimates for thermal maturity.The results suggest that shale-hosted organic matter from the shale is highly over-mature,and at this high thermal maturity organic porosity may be hosted primarily in solid bitumen.The Nuclear Magnetic Resonan（NMR）T₂ spectrum,shale mechanical characteristics,and displacement pressure measurements were used to study their relationships and characteristics of shale sealing ability.Different pressure and unloading rates of mechanical methods were used to study the sealing ability of the Wufeng-Longmaxi Formation shale.Shale sealing ability presents the shale gas conservation ability.Uploading procedure indicates the shale plastic increasing under high consicital pressure,and the shale sealing ability increasing.When the BR_ois bigger than 2.70%,the displacement pressure is bigger than 3.0MPa,the shale sealing ability is good.When the BR_ois bigger than 2.50%,elastic modulus is bigger than 20GPa,the sealing ability is good.When the shale sealing index（SSI）value is less than 300,this suggests the shale sealing ability is poor.When the SSI value is between 300 and 800,this suggests the shale sealing ability average,when the SSI value is bigger than 800,the shale sealing ability is good.Therefore,the N8,N6,N1,and Z1 wells shale sealing is good,the W4 and W5 wells shale sealing ability is average,and the Y1 and L2 wells shale sealing ability is poor.