Formation mechanism and enrichment patterns of middle-low rank coalbed methane in Southern Junggar Basin,China

The abundant coalbed methane exploration in the southeast margin of Junggar basin has not made a greater breakthrough for its complicated geological structure and reservoir formation mechanism. Therefore,its accumulation mechanism and main controlling factors become the most critical constraint issues for CBM exploration. On the basis of the fine dissection about geological conditions of the coalbed methane here,the characteristics of coalbed methane ac- cumulation and the reservoir formation mechanism were revealed. The authors found that the coal seams controlled by complicated geological structure,with east-west fault and anticline,were mainly developed in the Tianshan piedmont fault fold belt. And the coal seams and sandstone were superposed. Also the high porosity of coal has good pore con- nectivity. As a whole,the gas content is generally high in the West and low in the East. Therefore this paper estab- lished a mixed gas source enrichment model of the structure-hydraulic plugging type in the steeply inclined coal seam. And it is concluded that the sealing zone with relatively high pressure is the favorable area for coalbed methane accu- mulation. So the relatively high point of the structure and the transitional zone between surface water and groundwater should be optimized in the exploration of coalbed methane. Therefore,the authors suggest to carry out stereoscopic ex- ploration in the Fukang-Mount Huangshan favorable target area.