Study On The Law Of Gas Occurrence And Desorption Of Shale Gas Reservoir And Its Influencing Factors

Taking the shale developed in chang7 reservoir of Ordos Basin as the research object.Using X-Ray diffraction analyzer and geochemistry analysis analyzed the mineral composition,organic matter content,Kerogen component and maturity of organic matter of shale sample.Using Argon-ion milled and field emission scanning electron microscopy and CT scanning technique analyzed the types of reservoir space of shale sample.Based on mercury injection,nuclear magnetic resonance and low-temperature nitrogen adsorption conduct quantitative express to pore-size distribution and specific surface area.Based on isothermal adsorption experiment of methane and Knudsen number analyzed the occurrence characteristic of shale gas,then use the multiple linear regression to study the components of the shale on the adsorption of methane,analysis the factors affecting adsorption of methane desorption by calculate the isosteric adsorption heats and Limiting adsorption heat;The research result show that the adsorption state of shale gas is the main occurrence form,followed by free state,under the condition of reservoir temperature and pressure.The adsorption state shale gas occurrence on the surface of illite-smectite mixed-layer and organic matter in shale,the adsorption ability of organic matter is stronger than that of illite-smectite mixed-layer.Free gas in shale mainly occurs in mesopores,macro pore and fracture,adsorbed gas mainly exists in the pore surface with pore diameter of 1 ~ 3nm.The adsorption capacity have positive correlation to specific surface area,the abundance of organic matter and the relative content of illite-smectite mixed-layer of shale at constant temperature and pressure.The content of adsorbed gas increased with increasing pressure and the free gas increased with reducing pressure in a certain pressure range with constant temperature.The content of desorption increased with increasing temperature and the adsorbed gas increased with reducing temperature with constant pressure.Gas occurrence affected by external factors and internal factors.The external factors include temperature and pressure,the internal factors include organic matter abundance,relative content of illite-smectite mixed-layer and specific surface area in shale.