Well spacing optimization technology for coalbed methane horizontal wells

Background Well spacing design directly affects the resource utilization and exploitation benefits of blocks. Rational well spacing design plays a significant role in the commercial exploitation of coalbed methane (CBM) fields. Since the beginning of China’s 14th Five-Year Plan, blocks for CBM production in the southern Qinshui Basin have experienced a gradual increase in burial depth, a progressive decline in permeability, and a constant update of primary exploitation technology. Consequently, traditional well spacings fail to meet the requirements for field CBM exploitation any longer.

Methods This study investigated the western Qinnan – eastern Mabi block by combining numerical simulations with economic assessments. Using the geology-engineering economy integration approach and based on the mechanisms underlying pressure drop propagation and synergistic desorption, this study analyzed the factors influencing well spacings. Moreover, a flow chart for determining optimal CBM well spacings was established. Accordingly, the optimal well spacings under given economic parameters and varying combinations of geological conditions and engineering parameters were determined.

Results and Conclusion The results indicate that important factors influencing the well spacing include permeability, gas content, and fracture half-length, which exhibit positive correlations with the well spacing. For the CBM well spacing design, it is necessary to predict the production capacity and recovery degree under varying combinations of geological and engineering parameters using numerical simulation. The optimal well spacings should be calculated based on the calculation of economic limit well spacings, as well as the maximization of single-well estimated ultimate recovery (EUR), the rationalization of recovery degrees, and economic benefits. The chart board of optimal well spacings was established based on the actual geological, engineering, and economic parameters of the western Qinnan – eastern Mabi block, guiding field production practices and providing a reliable basis for the well spacing optimization design in the production capacity construction of the block. Conducting rational well spacing optimization using the geology-engineering economy integration approach by considering pressure drop propagation and synergistic desorption will be a significant trend in CBM production. The results of this study provide a valuable reference for the rational and efficient exploitation of CBM fields.