An adsorption-permeability model of coal with slippage effect under stress and temperature coupling condition

Abstract

Temperature and slippage effect, two important factors affecting coalbed methane (CBM) production, both have an intuitive effect on gas adsorption in coal seams and coal deformation and gas seepage processes. In order to simulate the process of CBM exploitation, isothermal adsorption tests at different temperatures and seepage tests under rising pore pressure were carried out. In this study, the modified Langmuir model considering the effects of temperature and excess adsorption was established. On this basis, the amount of adsorption deformation was calculated. The results show that the amount grows with the rise of pore pressure and is negatively related to temperature. In addition, a temperature mutation coefficient (γT) was introduced to characterize the response of coal permeability to temperature, and thermal expansion, thermal cracking, adsorption deformation induced by temperature and slippage effect were combined to establish a coal permeability model under the coupling of stress and temperature. Meanwhile, a helium parallel seepage test was carried out under the same conditions to study the effects of slippage and adsorption expansion. It is found that the rise of pore pressure will reduce permeability under the action of adsorption or slippage effects, and the rise of temperature will enhance the permeability. Finally, according to the experimental data, the adsorption-permeability model achieves better fitting results, compared with other models. The model can provide certain theoretical support for CBM exploitation.