Adsorption Isotherm Calculation and Mechanism of High Pressure and High Temperature Shale Gases

For high pressure and high temperature shale gases, the adsorption density would approach to or maybe more than the maximum density. To investigate the adsorption mechanism and calculate the adsorption isotherms, methane molecules adsorb into the organic nanopore under 0 to 80 MPa and 430 K are simulated using molecular dynamic method. Based on simulation results, the analytical model of adsorption isotherm in organic nanopores for high pressure and temperature is developed, which is verified by our adsorption isotherm measurements. Results reveal that for high pressure and temperature shale gases the adsorption mechanism is the free gas filling and the adsorbed layer is becoming compressed, the density of which is more than maximum density. The compressed adsorbed layers have high mobility and contribute to more gas production of deep- and ultra-deep shale gases. when the pressure decreases to less than 40 MPa, the mobility of adsorbed layers decreases. These results suggest the development of deep- and ultra-deep shale gases could take an advantage of high mobility adsorption and high pressure in small organic nanopores.