NUMERICAL INVESTIGATION OF HYDRAULIC FRACTURE PROPAGATION IN HETEROGENEOUS ROCKS USING THE DAMAGE MECHANICS MODEL

Abstract

In this study, we use a three-dimensional damage mechanics-based finite element model to investigate hydraulic fracture propagation in heterogeneous rocks. In the proposed finite element model, the Weibull random distribution function is adopted to characterize the rock mechanical heterogeneity of the elastic modulus. This damage mechanics model can well reflect the damage evolution of hydraulic fracture propagation in heterogeneous rocks under tensile and compression states. The fully coupled fluid-solid system of the hydraulic fracturing problem is numerically solved by the Newton-Raphson iterative method. Our numerical results show that key factors including the degree of mechanical heterogeneity, tensile strength, elastic modulus, and natural fractures have a significant impact on hydraulic fracture propagation in heterogeneous rocks. Both the damage zone and the first principal stress contour present a random distribution due to the mechanical heterogeneity. In a naturally fractured heterogeneous reservoir, the damage zone presents a banded distribution, which has the same dip angle of natural fractures. Some natural fractures away from the injection point are also partially opened under the combined action shear and normal stress field. This investigation provides new insight into the formation mechanisms of complex fracture networks in heterogeneous rocks.