Abstract:
The "double low" rate of exploration and utilization of CBM resources in China leads to a significant slowdown in CBM production, which has become a bottleneck restricting the development of CBM industry in China. The common CBM reservoir evaluation method did not pay enough attention to the hydro-fracturing potential, resulting in low discovery rate of high-quality gas reserves and low mobilization-rate of the present reserves. Thus, it is extremely necessary to do some research regarding to hydro-fracturing potential evaluation. Targeting on the Zhengzhuang CBM field of the southern Qinshui Basin, this study did comprehensive investigations including coal core analysis, physical simulation experiments on large rock samples, geological inversions of well logging and three-dimensional seismic data. Based on the comparison of the geological analysis results with the monitored fracture propagation in hydraulic fracturing, this study concluded five key influence factors for evaluating hydro-fracturing potential of CBM reservoir:i.e., the coal texture, coal macro-lithotype, coal seam structural deformation, in-situ stress, differences of tensile strength between coal seam and its roof/floor. Based on the analysis of above influence factors, a quantitative comprehensive evaluation model was proposed and applied for evaluating hydro-fracturing potential of the CBM reservoir in the Zhengzhuang field. The evaluation results were validated by the production data of more than 1 000 CBM wells. The study is important for predicating production target for the un-mobilized reserve area, and for adjusting or optimizing development plan in the mobilized reserve area.