Analytical models for coal permeability changes during coalbed methane recovery: Model comparison and performance evaluation

Abstract

Abstract An in depth comparison of four permeability models, Palmer and Mansoori (P&M) model, Shi and Durucan (S&D) model, Cui and Bustin (C&B) model and the improved P&M model, developed under uniaxial strain conditions prevailing in coalbed reservoirs, was carried out focusing on the relative influence of the matrix shrinkage term over the compaction term in each model. The ratio of the coefficients of the two terms is shown to have a direct impact on the magnitude of permeability rebound pressure, which is a key parameter controlling the modelled response of coalbed permeability to reservoir drawdown. P&M model and C&B model are found to yield essentially the same permeability rebound pressure, which is significantly lower than that given by S&D model. Cleat porosity change in P&M model has been shown to be controlled by the effective mean stress, indicating that it is essentially a mean stress model (as C&B model). With the introduction of an empirical parameter g (