EFFECT OF STRONG DENUDATION ON COALBED METHANE ENRICHMENT IN A STRONGLY DEFORMED ZONE: A CASE STUDY IN SOUTHERN QINSHUI BASIN, CHINA

摘要

The Upper Paleozoic strata in the southern Qinshui Basin was strongly deformed, and the prediction of CBM sweet spots in this area is difficult. Stress is an important factor affecting the permeability of coal reservoirs. Therefore, the influence of strong denudation on coalbed methane enrichment was studied in this paper. The results show that stress unloading, reduction of formation temperature, and tensile strain, all can lead to the reduction of the minimum principal stress in the erosion process. The cumulative reduction of minimum horiaontal stress for the No. 3 coal is generally less than 10 MPa. For the strongly deformed target layer, the fracture and fault systems are extremely developed. Therefore, in the region with a large erosion thickness, the degree of stress reduction is large, and the storage conditions are poor, so the productivity of the coalbed methane well is low. However, the storage conditions are better in regions with a small erosion thickness, therefore the coalbed methane was easily preserved. According to the research in this paper, the preservation effect is an important control factor for the accumulation of coalbed methane in the strongly deformed zone. For the No. 3 coal in the study area, the area with a denudation thickness of less than 2 000 m should be the sweet spots for the exploration of coalbed methane.