Development of crossflow models between coal and sandstone incoalbed methane reservoirs and influence factors analysis

The interlayer interference in multi-layer coal seams during exploitation of coalbed methane affects the accuracy of gas production prediction. In order to investigate the interlayer interference between coal seams and sandstone seams, the authors built crossflow models of gas phase and water phase. The model is based on the coupling theory and applies the Darcy's Law and dynamic permeability model of coal. The model was then implemented in Matlab, and cross flows under different conditions were computed. Factors that influence the interference intensity of coal seams and sandstone seams were analyzed. The simulation results show that permeability, elastic modulus of coal, and thickness of coal seams and sandstone seams have more significant influence on cross flow, while the Langmuir pressure of coal and permeability of sandstone have less significant influence on crossflow. On the condition of lower elastic modulus of coal (2 000 MPa) cross flow between coal seams and sandstone seams increases with the increment of the average pore pressure. The crossflow between coal seams and sandstone seams decreases firstly and then increases as the average pore pressure increases when the elastic modulus of coal is higher than 2 500 MPa. The thickness of sandstone seams has little influence on the cross flow when the average pore pressure is between 3 MPa and 4 MPa.