Occurrence characteristics and assessment of favorable areas of coalbed methane exploration in Liupanshui coalfield

Coalbed methane(CBM)development test has gotten significant progress in multiple blocks of Liupanshui coalfield during the last 5 years. There are many CBM accumulation units with different exploration and development conditions in the study area, so the overall evaluation of CBM occurrence characteristics and comprehensive prediction of favorable blocks are crucial for CBM development decisions in the area. The common features of different CBM accumulation units in Upper Permian coal-bearing formation is thin single seam, good cap rock of roof and floor, high gas content, high ground stress, poor coal structure, low porosity and permeability, generally high pressure coefficient, but larger differences in CBM resource abundance and resources, cumulative thickness of coal seam, structure, buried depth, coal rank, production test effect, exploration degree and ground conditions. After that, three second-order indices(resource condition, reservoir condition and developmental foundation condition)and their corresponding nine third-order indices for CBM comprehensive development assessment are established. The comprehensive evaluation and ranking result of 22 CBM accumulation units in the study area is determined by the fuzzy mathematics for favorable block selection. The results show that five CBM accumulation units are favorable blocks for priority development, nine CBM accumulation units are the more favorable areas recommended substituting development, and eight CBM accumulation units are the prospective areas.