Well type and pattern optimization method based on fine numerical simulation in coal-bed methane reservoir

Coal-bed methane (CBM) is a precious clean energy. A reasonable well type and pattern design is the premise and the key to effective development of coal-bed methane. In this paper, a set of optimization method is presented which includes a fine CBM numerical model with the combination of the isothermal adsorption test results. Different Langmuir curves and adsorption-desorption time are corresponding to different grids in the model. The model has advantages over previous models in terms of the CBM reservoir structural characteristics and permeability anisotropy. As in most of CBM mining area, the structural characteristics are so complex that a combination of vertical and U-shaped wells is the best choice to achieve optimum production of gas. To optimize the pattern and spacing between vertical wells, different types of coal-bed cleats pressure drop rules are in consideration. Based on the CBM content in the reservoir, the distribution of different well types can be determined. The optimization method above has been applied in one pilot area in QinDuan Block, China. The result shows that combination of U-shaped and vertical wells in a diamond well pattern will provide the best CBM production scenario. In this diamond well pattern, the optimum well spacing along the long and short diagonals is 350 and 300 m, respectively. The degree of reserve recovery was predicted to up to 56.63 % after 30 years of production.