A Review on Recent Advances in the Numerical Simulation for Coalbed Methane Recovery Process

Abstract

Abstract The recent advances in numerical simulation for primary and enhanced coalbed methane (CBM/ECBM) recovery processes are reviewed, focusing primarily on the progress that have occurred since a similar review paper was published by King and Ertekin in 19891,2. Two major issues regarding the numerical modeling will be focused on in this review: firstly, multicomponent gas transport in in-situ bulk coal and secondly, changes of coal properties during methane production. For the former issues, a detailed review of more recent advances in modeling gas and water transport within coal matrix is presented. Further, various factors influcing gas diffusion through coal matrix will be highlighted as well, such as pore structure, concentration and pressure, and water effects. An ongoing bottleneck for evaluating total mass transport rate is developing a reasonable representation of multi-scale pore space that considers coal type and rank. Moreover, few efforts have been involved to model water flow behavior in coal matrix and its effects on both CH4 production and on the exchange of CO2 and CH4. As for second issue, theoretical coupled fluid flow and geomechanical models have been proposed to describe the evolution of pore structure during methane production, instead of traditional empirical equations. However, there is currently no effective coupled model for engineering applications. Future perspectives of developing suitable simulation models for CBM production and predicting CO2-sequestration ECBM recovery are suggested.