Accumulation mode of middle-low rank coalbed methane in Houxia Basin，Xinjiang

There are successful cases of large-scale CBM development of low-rank coal abroad. Though China is rich in low-rank CBM resources, their exploration and development progress is slow. Considering the low exploration degree and for the purpose of further understanding the accumulation conditions of medium-low rank CBM and guiding exploration practice in Houxia Basin, seismic and geological analysis, as well as coal petrography analysis and drainage production data of drilled wells are carried out in the study area. The results show that the coal seams are characterized by complex structure, large thickness (4.1-24.3 m), stable development, large difference in gas content (1.16-12.30 m³/t), good physical properties and large permeability (1.61-13.30)×10⁻³ μm². There are four genetic types of CBM: thermal origin, secondary thermal origin, mixed origin and biological origin. Under this condition, combined with structural evolution, hydrogeology and preservation conditions of the coal seam roof and floor, three accumulation models of deep thermal origin, secondary thermal origin of conventional traps and medium shallow slope biogenic gas are formed. Each mode represents the concentration processes of different types CBM. It is considered that the medium-low rank CBM in this study area can form a favorable resource concentration area under the matched structural, hydrological, and roof and floor sealing conditions. Among the accumulation modes, deep thermal origin and secondary thermal origin of conventional traps are more favorable for accumulation, and the corresponding areas are favorable for future exploration and development.