(518e) Modeling of Multicomponent Sorption in Ecbm Processes

Enhanced coalbed methane (ECBM) recovery by injection of CO2 or by injection of mixtures of CO2 and N2 has been demonstrated to recover additional natural gas resources while at the same time sequestering CO2 in the subsurface. The dynamics of ECBM recovery processes are determined in large part by the sorption behavior of mixtures of CH4, CO2 and N2 on the coal surface. Conventional simulation tools use the extended Langmuir model for predicting the sorption behavior of the gas mixtures that form during a displacement process. In previous work, we demonstrated the accuracy of this approach for binary CH4/CO2 and CH4/N2 displacements by comparison to lab scale experiments. The extended Langmuir model was unable to describe the behavior of ternary CH4/CO2/N2 displacements. Adsorption hysteresis is a complicating factor also. This paper investigates the accuracy of ternary gas displacement calculations. We find that a sorption model more sophisticated than the extended Langmuir model is needed to represent the dynamics of multicomponent systems. We use the Ideal Adsorbate Solution model (IAS) and compare the predicted behavior to standard calculations and experimental results.