Numerical analysis of drainage rate in multi-layer coalbed methane development in Western Guizhou, Southern China

Abstract

In Western Guizhou, China, multi-layer development is a successful way for CBM development, with drainage rate control being the essential technology. In this article, a coupled hydraulic-mechanical numerical model considering permeability velocity-sensitive damage was established to analyze the impact of drainage rate on the gas production and reservoir parameters of multi-layer CBM development. The CBM development in the study area can be divided into four stages. The permeability velocity-sensitive damage and Jamin effect mainly occurred in the first two stages. Increasing the drainage rate during the first two stages will cause more serious permeability velocity-sensitive damage. Reducing the drainage rate in the first two stages could alleviate the permeability velocity-sensitive damage and Jamin effect. During the stable production stage II, the gas seepage being dominant in the c409 coal seam, the gas production would be significantly reduced under the permeability stress-sensitive damage as the drainage rate increasing. Based on the simulation results, three recommendations concerning the drainage rate optimization of multi-layer CBM development were advanced, and gas production was successfully improved. This study has important theoretical and practical significance for guiding the multi-layer CBM development in Western Guizhou and Southern China.