ANALYSIS OF THE INFLUENCEOF FRACTURED COAL JOINTS ON HYDRAULIC CRACK PROPAGATION AND TURNING

Fragmented coal seams are widely distributed and rich in coal-bed methane resources. The effective development of coal-bed methane can alleviate energy tensions. However, the fractured coal joints are very developed, which affects the expansion of fractures during the fracturing process, and it also affects the safe and efficient development of coalbed methane. In addition, the influence of joints will cause fractures to inject fracturing fluid into deep formations, causing formation and environmental pollution. Therefore, in this paper, based on the ABAQUS finite element platform, the mechanism of fractured coal joints on hydraulic fracture propagation behavior during fracturing is analyzed. The results show that the increase of the joint dip is beneficial to the extension of the crack in the Y direction, but it is not conducive to its expansion in the X direction. When the joint dip angle is 75 degrees, the distance of cracks in the X direction is 30.68 m less than that when the joint dip angle is 30 degrees, and when the joint dip angle is 75 degrees, the distance of cracks in the Y direction is 25.78 m longer than when the joint dip angle is 30 degrees. The joint density has little influence on the propagation of cracks in the X direction, but has a greater influence on the propagation of cracks in the Y direction. Moreover, the study also found that coal seam joints with higher strength can prevent hydraulic fractures from expanding in any direction. When the joint strength is 0.75 MPa, the extension distance of the crack in the X direction is 52.31 m, and when the joint strength increases to 2.25 MPa, the extension distance of the crack in the X direction is shortened to 19.54 m. The research can provide a reference for improving the prevention of fracturing fluid pollution during the development of coalbed methane in fragmented coal.