Stochastic modelling of coalbed methane resources: A case study in Southeast Qinshui Basin, China

This paper presents a stochastic analysis of coalbed methane (CBM) resources for a coal seam in southeast Qinshui Basin, China. Log and laboratory data are used to predict the coal thickness, coal ash content and coal gas content. Using reservoir modelling, the distributions of the karst collapse column (KCC), coal seam thickness, coal quality and coal gas content are generated. The convergent interpolation and sequential Gaussian simulation methods are used to model the surface and structure of the coal seam. The structural models are determined by the surface structure and coal seam thickness. Based on the structural models, the coal and KCC are converted to two facies and their distributions are obtained using object modelling. The coal density distributions are simulated based on each facies model using the sequential Gaussian simulation. Finally, different realisations are used to study CBM resources. The results show that the heterogeneities in coal seam thickness and coal quality lead to significant uncertainty in estimating CBM resources. A model with lower heterogeneity gives a greater CBM resource. The distributions of KCC, coal seam thickness, coal quality and gas content are the main sources for uncertainty in CBM resource estimation. The density variogram and top structure contribute less to the uncertainty in CBM resources.