Controlling geological factors and coalbed methane enrichment areas in southern Wuxiang block,Qinshui Basin

Using the coal samples from the Carboniferous-Permian Taiyuan Formation (No.5) and Shanxi Formation (No.3) in southern Wuxiang block, Qinshui Basin, Shanxi province, the authors studied the sedimentary facies, geological structures, gas-bearing property, and coal seam occurrence characteristics, investigated the main geological controlling factors of coalbed methane (CBM) enrichment, and comprehensively evaluated the CBM favorable enrichment areas based on the fuzzy mathematics evaluation and analytic hierarchy process method. The results show that① the peat flat in the Taiyuan Formation, and the peat swamp in the Shanxi Formation are the most favorable facies belts for the development of coal seams.②The No.15 coal seam of the Taiyuan Formation and the No.3 coal seam of the Shanxi Formation have the same occurrence pattern. They are monoclinic structures with a north-northeast strike and a westward dipping trend. The buried depth deepens gradually from east to west. The thickness of the No.15 coal seam increases gradually from southwest to northeast, and the No.3 coal seam gradually thickens from north to south as a whole.③The larger coal thickness and buried depth, the better sealing ability with sandy mudstone/mudstone, and simple geological structures or with developed reverse faults will benefit the increase of gas content in coal reservoirs.④Finally, the comprehensive evaluated results using multi-level fuzzy mathematics indicate that the CBM favorable enrichment areas of the No.15 and No.3 coal seams are the areas surrounding the exploration wells of W26-W31-W41 and W1-W20-W2 respectively.