Experimental Investigation of the Effect of Bedding Planes on Hydraulic Fracturing Under True Triaxial Stress

A bedding plane effect occurs when hydraulic fractures encounter the bedding plane. True triaxial hydraulic fracturing experiments were conducted with test blocks containing bedding planes. The effects of bedding plane properties and stress state on fracture propagation were analyzed. When hydraulic fracture encounters the bedding plane in sedimentary stratum, it usually propagates along the bedding plane at first. When the hydraulic pressure increases to a critical value in the direction of main hydraulic fracture, the main hydraulic fracture continues propagating along the original direction. The length of the long axial of the hydraulic fracture propagating along the bedding plane is greater than the length of the main hydraulic fracture before penetrating the bedding plane, and both of them are greater than the length of the main hydraulic fracture after penetrating the bedding plane. Three-dimensional propagation models were established. Three propagation forms of hydraulic fractures existed when encountering bedding planes: (1) propagation along the bedding plane; (2) initial propagation along the bedding plane followed by penetration of the bedding plane and propagation along the principal direction; and (3) direct penetration of the bedding plane and propagation along the principal direction.