Geological Characteristics Affecting Coalbed Methane: A Case Study in the Anze Area, Southern Qinshui Basin

The main purpose of this study was to investigate the geological characteristics affecting coalbed methane (CBM) enrichment in the Anze area in China for the exploitation of methane and predicting optimum CBM enrichment. To study methane enrichment, we developed maps of coal structure via correspondence analysis, used rescaled-range (R/S) analysis to assess the degree of development of fractures, measured adsorption capacities of methane in coal, and determined present-day methane contents and vitrinite-reflectance values at depths of ~ 800–1200 m in the southeastern Qinshui Basin. The results showed the following. (1) Coals in the Anze coalfield exhibited high adsorption capacities, which affect coal rank, but adsorption capacities in the eastern and southern parts were greater than those in the western and northern parts. (2) Both the upper and lower parts of the coalfield were characterized by primary coal and detrital coal, whereas the middle part mostly contained granular coal. This is a typical interbedded structure that is divided clearly into three types. Reservoir conditions in the northern and southern parts near well A1, which revealed distinctly thick beds of primary and cataclastic coal, were more favorable compared with other southern areas and south-central parts. (3) Per the R/S analysis, the reservoir fractal dimension was large in the fault-development zone in the middle part, especially near the major faults F1 and F2 in the south-central parts. Reservoir conditions in the northern parts and near wells A1, A10, and A19 in the southern parts were more favorable compared than those in the area near faults F1 and F2.