Optimizing the drilled well patterns for CBM recovery via numerical simulations and data envelopment analysis

Coalbed methane (CBM) commercial development requires choosing the arrangement of the wells. This should be done by considering the corresponding input-output (investment-profit) efficiencies. Simulations were obtained from the computer modeling group (CMG) given the reservoir conditions of the Panzhuang block in the southern part of the Qinshui Basin. This is a demonstration region for CBM development located in Shanxi province of northern China. The sensitivity of gas production from a single vertical well to the primary reservoir parameters was estimated first. Then multi-well gas production from three different well patterns was simulated to estimate the most appropriate well spacing. Combining the investment requirements then gave investment-profit efficiencies for these well patterns. A data envelopment analysis (DEA) model was used to optimize the efficiency. The results show that the permeability, the reservoir pressure, and the gas content have an evident impact on single well gas production. The desorption time has little or no affect on production. The equilateral triangular well pattern (ETWP) in a 400 m well spacing is, for multi-well development, the optimal pattern. It has a better input-output ratio, a longer stable yield time, and provides for greater CBM recovery than does either the rectangular well pattern (RWP) or the five point well pattern (FPWP).