Coupling effect and optimization application of key parameters for hydraulic fracturing in deep coal seams

Coal-rock reservoirs develop a large number of weak planes such as cleats, bedding planes, and natural fractures, with complex pore structures, making it difficult to predict the fracture propagation morphology during hydraulic fracturing. Clarifying the intersection and propagation laws of weakly consolidated planes in coal seams with hydraulic fractures is conducive to achieving comprehensive and effective permeability enhancement through coal seam fracturing. Based on the cohesive element method, considering the occurrence of weakly consolidated planes and their distance from perforations, a hydraulic fracturing fracture propagation model for weakly consolidated planes was established. The influence of the length-distance ratio (the ratio of the length of the weakly consolidated plane to the distance from the injection point to the center point of the weakly consolidated plane) on the intersection and propagation laws of hydraulic fractures under different approach angles and strengths of weakly consolidated planes was analyzed. Through orthogonal analysis using the response surface methodology, a coupling correlation model of key parameters between fracturing fluid displacement, approach angle, length-distance ratio, and fracture propagation capacity was established. The influence of multiple parameters on the evaluation indexes of hydraulic fracture propagation in deep coal seams was studied, realizing the multi-parameter optimization of deep coal seam fracturing. The research results show that the order of influence of the parameters according to the degree of impact is: fracturing fluid displacement > approach angle > length-distance ratio.