Thermodynamic models for swelling of unconfined coal due to adsorption of mixed gases

摘要: Permeability evolution in coal seams during CO2-Enhanced Coalbed Methane (ECBM) production is strongly influenced by swelling/shrinkage effects related to sorption and desorption of both CO2 CH4. Other gases, such as N2, have also been proposed for injection ECBM operations. In addition, water vapour will almost always be naturally present. Much work has done on the sorption/swelling response exposed pure gases. However, address in-situ coal-seam conditions realistically, an understanding swelling behaviour matrix material due multiple-species adsorption needed. Here, we construct new thermodynamic models unconfined multiple gas/fluid species, addressing equilibrium state focusing a binary gas mixture. Four are derived, covering three possible end-member interactions, plus generalized case. The considered correspond gases α β at fully separate sites, shared sites partially (Models 1–3, respectively). We compare our model predictions with literature data Bowen Basin CH4/CO2 mixtures total pressures up 15 MPa 55 °C. results show that CO2/CH4 best explained Model 3, which turn implies this case determined partial pressure selective (affinity) effects. 3 easy parameterize its applicability specific coals easily evaluated. Though more difficult parameterize, (Model 4) can applied any rank, It therefore offers important tool modeling permeability