Sweet-spot prediction about coalbed methane development in the areas with complex hydrogeological conditions

In the area with complex hydrogeological conditions, the water abundance of surrounding rock and the amount of replenishment to the coal seam is of an important impact on the propagation speed of pressure in the coal seam during drainage, and are the key parameters to be considered in the sweet spot of coalbed methane development. Taking the 15# coal seam in Shouyang Block as the research object, the evaluation indexes system of coalbed methane development sweet spot including key hydrogeological parameters is constructed by fully considering the water abundance and recharge of surrounding rock, combining with regional geology, resource geology, recoverability and removability. The multi-level fuzzy comprehensive evaluation method is applied to predict the sweet spot of coalbed methane development. The prediction results are compared with those without considering hydrogeological conditions. The results are verified by the actual gas production of coalbed methane wells. The results show that the northeastern and southwestern parts of the study area are the sweet spot areas for CBM development. The prediction results of the sweet spot areas for CBM development considering the differences in the main parameters of hydrogeological conditions better reflect the objective facts. When the recharged water of the surrounding rock of the coal-bed gas well is small, the prediction results ignoring the differences in hydrogeological conditions are similar to the actual ones. When the surrounding rock supply is large during the drainage process, the supply water of surrounding rock and the water in the coal seam jointly compete for the fissure channel, which affects the propagation speed of water pressure in the coal seam and affects the gas production of the coalbed methane well.