Study on the interaction and propagation patterns of weakly consolidated interfaces and hydraulic fractures in deep coal seams

Coal seam reservoirs contain a large number of weakly consolidated interfaces such as cleats, bedding, and natural fractures, which, along with complex pore structures, make the prediction of fracture propagation patterns during hydraulic fracturing challenging. Understanding the intersection and expansion rules of hydraulic fractures with coal seam weakly consolidated interfaces can facilitate comprehensive and effective permeability enhancement in coal seams through fracturing. We establish a model for the expansion of hydraulic fractures on weakly consolidated interfaces based on the cohesive element method, considering the occurrence of weakly consolidated interfaces and their distance from the perforations, analyze the impact of different approach angles and strengths of weakly consolidated interfaces on the intersection and expansion patterns of hydraulic fractures at different length to distance ratios (the ratio of the weakly consolidated interface length (L) to the distance (D) from the injection point to the center of the interface). The results indicate that when the length to distance ratio (L/D) is 1/3, 2/3, 1/1, as the approach angle increases, so does the fracture deflection angle; when L/D is 1/3 or 2/3, the total fracture length gradually decreases with increasing approach angle; when the aspect ratio is 1/1, the total fracture length gradually increases with the increase of the approach angle; when the approach angle is ≤15°, hydraulic fractures are more likely to extend along the direction of the weakly consolidated interfaces after intersection, whereas when the approach angle is ≥30°, hydraulic fractures tend to penetrate the weakly consolidated interfaces; the fracture width is maximum when the approach angle is 30°; as the strength of the weakly consolidated interfaces increases, both the fracture deflection angle and the modified fracture length show an increasing trend.