The study on mechanics of hydraulic fracture propagation direction in shale and numerical simulation

Disciplinarians of hydraulic fractures propagation direction can make engineering decisions and suggestions for shale gas reservoir reformation. Based on the strain energy density factor theory, the relationships of fracture surface water pressure, fracture dip, and confining pressure ratio on hydraulic fracture propagation angle are studied. The extended finite element method is used to analysis the influences of bedding plane, natural fracture and horizontal stress difference on fracture propagation characteristics. When water pressure is less than maximum horizontal principal stress (sigma(H)), there is a critical fracture surface inclination angle, and fractures propagation direction is reversed along the original fracture line. When the pressure is equal to sigma(H), fracture propagation angle increases with dip angle of the fracture surface, and is independent of the stress state. When water pressure is greater than sigma(H), fracture propagation angle increases first and then decreases. When the angle between bedding plane and sigma(H) is small, hydraulic fractures propagation direction extends along the sigma(H), conversely, along the bedding plane. The smaller horizontal stress difference is, the easier hydraulic fracture tends to be perpendicular to natural fracture, and the hydraulic fractures propagation direction easier to parallel to natural fracture in natural fracture.