Supercritical isothermal adsorption characteristics of shale gas based on gravimetric method

In order to analyze the supercritical adsorption characteristics of shale gas effectively,using the isothermal adsorption instrument based on gravimetric method,by means of the high precision magnetic suspension balance sys- tem,the density of methane and its excess adsorption were directly tested under the conditions of different pressures. The results show that when the pressure is low,the excess adsorption quantity increases with pressure;when the pres- sure is higher than 8 MPa,the excess adsorption quantity will decline with the increase of pressure. This is mainly due to the difference of methane density at adsorbed phase and free phase. When the pressure is very high,the isothermal adsorption curve of supercritical methane must have a downward trend. It is not an abnormal phenomenon,but the es- sence characteristics of the excess adsorption quantity of supercritical methane. In addition,the excess methane adsorp- tion capacity decrease linearly with pressure at high pressure,so the method for calculating the methane adsorption phase volume is determined. And the absolute adsorption quantity are corrected by the assumption that the volume of methane at adsorbed phase is constant. The correction results show that the absolute adsorption quantity of methane on shale can still be simulated and analyzed by the Langmuir adsorption model. The existing adsorption theory can be ex- tended to the field of supercritical temperature.