EXPERIMENTAL STUDY ON BREAKTHROUGH PERFORMANCE AND METHANE ADSORPTION PERFORMANCE OF SHALE GAS RESERVOIRS IN LONGMAXI FORMATION, SOUTHERN SICHUAN BASIN, CHINA

Based on the capping breakthrough experiment, this paper obtains the migration breakthrough performance of methane in shale reservoirs through parallel stratigraphic and vertical stratigraphic samples. The methane adsorption model is optimized and the adsorption properties of the adsorbed and free methane in the reservoir have been discussed. It is found that the methane molecules are mainly diffuse and transported in the parallel stratum direction in the reservoir. The vertical breakthrough is difficult, the breakthrough radius is small, and the reservoir has the characteristics of vertical self closing and parallel beam direction short-distance migration. The LF model is used to retrieve the theoretical gas content of adsorbed gas in shale under different buried depths. The theoretical maximum buried depth of adsorbed gas content is about 700m. After that, the content of adsorbed gas decreases with the increase of buried depth. The free gas is calculated based on the ideal gas state equation. The theoretical gas content and free gas content are basically unchanged after the burial depth increases first, and the maximum theoretical free gas content is between 0.99 and 3.93 m(3)/t. With the increase of burial depth, the total gas content shows a trend of rapidly increasing first and then decreasing slowly. The total gas content of shale gas is less affected by ground temperature, and reservoir pressure is the main factor controlling total gas content. The total gas content of shale gas in southern Sichuan is between 0.08-5.67 m(3)/t, and the critical transition depth from shale gas adsorption to free gas is between 1300-4900m.