Fu County, Ordos Basin Area Of ​​continental Shale Gas Adsorption And Desorption Studies

China shale gas resource is rich, have already begun to exploit in the Sichuan and Ordos Basin. Shale gas has a large amount of adsorbed gas, and the content is20%～80%. Shale gas mining process, the later period of stable resources mainly come from desorption of adsorbed gas. Therefore, it is necessary for shale gas adsorption and desorption to study, the research on this aspect at home and abroad is less. This paper takes continental shale gas as study object in Ordos Basin Fu Xian area. Studying on the characteristics of adsorption and desorption and desorption methods adopt to combine experimental with theoretical. The results are as follows:(1) The mineral of Fu Xian District continental shale are mainly clay minerals and quartz, about50.7%and23.39%partly. Pyrite is about8.48%. Plagioclase is approximately5.41%. The calcite is approximately2.66%and a little dolomite. Clay minerals are mainly illite and montmorillonite mixed layer, and relative content is about58.1%. The relative content of illite、chlorite and kaolinite is23%、12.7%and6%respectively.(2) The average content of organic carbon is2.38%, maturity is greater than1.0%. Kerogen type is sapropel (Ⅰ) and mixed-type (Ⅱ). Nanopores and microporous are the main pores of shale reservoir, and pore radius distribution from lnm to5nm. The average surface area is2.6m2/g. The average porosity is2.5%. The average permeability is0.035×10-3μm.(3) Using the adsorption and desorption of self-designed experimental device with volume method to study shale samples adsorption and desorption, which adsorbate is pure CH4, CO2and N2, under the temperature of30℃,45℃,60℃respectively. The experimental results show that different shale samples have different CH4adsorption isotherms which have the same trend at different temperatures. The amount of adsorption quantity increases with raising pressure, then slowly increases to the saturation adsorption. All samples desorption isotherms shows hysteresis.(4) Under the same pressure, different samples adsorbed gases show the higher the temperature, the smaller the adsorption quantity. On the formation condition, shale samples of adsorbed and free gases relative quantity distribution from37.22%to48.73%as well as from51.27%to62.78%respectively.(5)The half pore width distribution of the shale gas reservoir is described using weibull statistical distribution, and the half pore width adsorption-desorption model is derived combined with the molecular potential energy model. The average relative error between model fit results and experimental data is2.9%averagely, which indicates that the half pore width model is suitable for the shale adsorption and desorption experiments.(6) Shale gas CO2injection displacement desorption experimental study shows that production from8.259MPa to8.259MPa, step-down desorption of recovery ratio was72.62%. Core of total residual gas is27.38%, the adsorbed gas and free gas content is23.12%and4.26%, respectively. CO2injection displacement desorption oil recovery was80.29%, the core of total residual gas is19.71%, among of adsorbed gas and free gas were15.51%and 4.2%respectively. Results show that CO2injection displacement desorption is7.66%higher than step-down desorption of recovery ratio, CO2injection displacement desorption effect is better. Different time CO2injection displacement desorption experiments have same effect.