Numerical simulation on hydraulic fracture propagation in deep conglomerate reservoirs

Hydraulic fracturing is a technology that has become essential for the efficient development of deep conglomerate reservoirs. The disordered distribution of gravel in conglomerate reservoirs leads to strong heterogeneity, which induces a high degree of uncertainty in fracture propagation. In this study, a multi-field coupled numerical model of stress–seepage—damage based on the global cohesive element method is developed. The multi-scale mechanical characteristics of the matrix–gravel—interface ternary are systematically characterized, and the effect of horizontal stress difference, gravel content, and gravel particle size on the fracture propagation behavior is discussed. The results show that as the gravel content increases, the fracture initiation pressure increases, the fracture length decreases, and the fractures become more complex. Under low stress differences, the fracture tends to deflect around gravel when it encounters gravel. Under high stress differences, the fracture length decreases, and the fracture tends to penetrate through the gravel extension and is accompanied by termination at the gravel. A stress difference increases from 5 to 15 MPa, reducing fracture length by 19.8%. When hydraulic fractures encounter small-sized gravels and large-sized gravels, the dominant propagation behavior exhibits deflection around the gravel. And when hydraulic fractures encounter medium-sized gravels, the dominant propagation behavior exhibits penetration through the gravel. This study aims to deepen the understanding of hydraulic fracture expansion in deep conglomerate reservoirs and provides theoretical support for fracturing treatment design in conglomerate reservoirs.