Vertical grid optimization of numerical simulation of coalbed methane reservoir

Numerical simulation is a common method for the research of coalbed methane(CBM)reservoir engineering. However, the effect of the vertical grid size for the simulation results are often ignored when modeling. So, the behavior of fluid-flow in vertical grids, the gravitational differentiation of gas and water, and the pressure drop funnel are not accurately reflected, which have great influence on the simulation results. In order to study the influence of vertical grid division on numerical simulation of CBM production process, different simulators are used to simulate different longitudinal grid sizes. Permeability equivalent method, local grid refinement(LGR)method and new fracturing method in simulator are used to simulate fracturing. 15 schemes of 3 methods were simulated. The results show that the vertical grid division has great influence on the production, when the grid size is 1.5 m, the calculation results are more accurate, which can satisfy the simulation demand. The reasonable division of vertical grid can better show the phenomenon of gas and moisture difference in layers, and help to analyze the flow state of liquids, at the same time, is in favor of history matching and production prediction.