Abstract:
In order to study the adsorption mechanism of shale for gas, the isothermal adsorption experiments on shale samples from wells Fengcan 1 and Tianma 1 in Guizhou Province were carried out at 50℃, 60℃, 80℃, and the isothermal adsorption curves of CH
4 and CO
2 were plotted, the shale surface free energy was calculated and the adsorption characteristics of CH
4 and CO
2 from shale were analyzed by the surface free energy. The results show that when the temperature is constant, the surface free energy of shale gas increases with the increase of pressure, and the change of surface free energy of two gases shows an increasing trend. When the pressure is constant, the surface free energy decreases with the increase of temperature, which is consistent with the change of gas adsorption on the isothermal adsorption curve. The surface free energy of CO
2 is higher than that of CH
4 in shale. The surface free energy of shale to CO
2 is greater than CH
4, indicating that shale adsorption capacity for CO
2 is stronger than CH
4, and the rate of recovery can increase by injecting CO
2 into shale layers. For shale gas reservoirs with strong adsorption capacity, surfactants can be injected to enhance the binding capacity of shale surface and to reduce CH
4 surface area and shale surface free energy, so as to achieve the purpose of CH
4 desorption.