Numerical Simulation Of Well Patterns Optimization On CBM Development

Low coal rank coal contains about 47% CBM resources of the national CBM resources, related theory research of low coal rank CBM reservoirs under complex geological conditions has important theoretical and application value. Capacity and pressure distribution of complicatedly geologic CBM reservoir with multi-well exploitation were researched based on coal-bed gas geology, permeation fluid mechanics and finite difference theory by the method of theoretical research and numerical simulation, the reasonable well pattern arrangement was studied, that provides basis and guidance for CBM ground development.Coal was abstracted as double-porosity media. Dual porosity-single permeability CBM seepage mathematical model considering the matrix shrinkage duing to fluid pressure change were established.CBM seepage mathematical model were discreted by implicit difference method, CBM seepage numerical model were deduced which can be solved by iteration.Complicatedly geologic CBM reservoir model considering igneous rocks and faults was established on the background of Fuxin LiuJia CBM block. The off-take potential and pressure distribution of complicatedly geologic CBM reservoir were simulated and researched based on the mathematical model, numerical model and geologic model. The correctness of mathematical model and geologic model was proved through comparing numerical simulation results with actual production data. The simulation results shows that pressure distribution after extracting CBM are influenced by the geological factor. the way of pressure distribution is changed due to the close geologic structure, pressure spreading along the strike of intrusive dykes and faults, reservoir pressure gradient is greater in the place of igneous rocks and faults.The influence of face cleat permeability, butt cleat permeability, geologic model and complicatedly geologic structure on off-take potential and pressure distribution were analysed. Daily production is higher and the area of well interference is larger without considering the difference of face cleat and butt cleat. Initial reserves and daily production using geological model deviate from actual ideal geological model. There are three different patterns of CBM wells productivity in complicated geological reservoir comparing with ordinary reservoir based on the different distance from well to intrusive dykes and faults, pressure distribution and well interference of complicated geological reservoir are different from ordinary reservoir.Reasonable well spacing of complex geological CBM was analyzed. Well pattern arrangement is influenced by geological structure. The capacity of CBM well increases along with the increase of well distance with faults. When the distance of CBM wells and intrusive rocks equal to pressing crack radius, the capacity of CBM well is the largest. Wells spacing should increase appropriately in the direction of face cleat and in the place of intrusive rocks, that can make well interference form at the same time.Well patterns was optimized and well patterns density was analysed based on the analysis of the CBM well spacing. The more wells,the shorter time of well interference generation,and the larger capacity and net earnings.In LiuJia block,when wells exceed 22, the improvement of block capacity is not obvious.