Evaluation of favorable regions for multi-seam coalbed methane joint exploitation based on a fuzzy model: A case study in southern Qinshui Basin, China

Abstract

The coalbed methane resources in the Taiyuan Formation account for 55% of total coalbed methane reserves in the southern Qinshui Basin, China; however, the resources have yet to be utilized basically. The joint exploitation of coalbed methane in the Taiyuan Formation and the Shanxi Formation can accelerate the process of coalbed methane scale development in this region. The productivity characteristics of commingling drainage are controlled by various geological factors. Thus, to select favorable regions for multi-seam coalbed methane joint exploitation, the impacts of some geological factors such as coal thickness, burial depth, gas content, reservoir pressure gradient, and reduced water level on the gas production were analyzed and estimated based on a bivariate correlation analysis. Analysis results show that the two coal seams of the high production rate wells of commingling drainage usually have the following conditions: total coal thickness > 9.5 m; average burial depth < 640 m; average gas content > 14 m3/t; reservoir pressure gradient difference < 0.05 MPa/100 m; reduced water level difference < 55 m. Based on the correlation analysis results, the potential of multi-seam coalbed methane exploitation in the study area was evaluated by using a multi-objective fuzzy matter-element model. At last, taking the evaluation coefficient 0.75 as the critical value, unfavorable zones, relatively favorable zones, favorable zones, and extremely favorable zones for multi-seam coalbed methane joint exploitation were identified in the southern Qinshui Basin.