Quantification of Gas and Water Transfer Between Coal Matrix and Cleat Network During Drainage Process

Abstract

Mathematical models were developed in this study to quantify the gas and water transfer between coal matrix and cleat network during coalbed methane (CBM) drainage, which can be helpful to achieve some useful findings on features of fluid migration within coal reservoirs during drainage process. A typical CBM well located at southern Qinshui basin of China was selected as the case study. The ineffective critical porosity was defined and was used to acquire fluid transfer as a key parameter of the established model. Results showed that both the gas and water transfer controlled the drainage performances. Water drained from cleat was found to be the main reason for the decrease in the reservoir pressure at the early drainage stage, while the water transfer became significantly more important with the continuation of the drainage process. The first peak of gas production was controlled by gas desorption, and the subsequent peaks were influenced by the gas transfer.