Surface free energy of shale gas in Niutitang Formation in Guizhou Province

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 CH₄ and CO₂ were plotted, the shale surface free energy was calculated and the adsorption characteristics of CH₄ and CO₂ 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 CO₂ is higher than that of CH₄ in shale. The surface free energy of shale to CO₂ is greater than CH₄, indicating that shale adsorption capacity for CO₂ is stronger than CH₄, and the rate of recovery can increase by injecting CO₂ 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 CH₄ surface area and shale surface free energy, so as to achieve the purpose of CH₄ desorption.