Predicting the engineering sweet spot of coal-bed methane reservoirs: a case study from Central China

In this paper, a model for predicting the “sweet spots” of favorable areas of coal-bed methane (CBM) reservoirs was proposed. Four parameters were calculated using the proposed model combining the well logging and experimental data of coal cores, which are coal structure parameters, brittleness index, fracture development, and geostress. Furthermore, a quantitative characterization model for the engineering sweet spot of CBM reservoirs was established, which divided the reservoirs into categories I, II, III, and IV in the descending order of quality (fractureability). Most of the well blocks in the research area (Hancheng Coal Mine, China) were classified as type I and type II, where type II engineering sweet spots were often located around type I regions. Finally, the areas with the most potential for CBM development were identified, and the proposed model was verified by the development of a representative well and the measurement of its natural gas production. The gas production of a selected type I well is 852 m 3 /day (30 days after fracturing), which is in line with the predicted results.