Mode I and Mode II Fracture Toughness of Montney Shale

Hydraulic fracturing (HF) is an indispensable technique in the exploitation of the Montney formation, one of the largest shale gas plays in North America, due to its ultra-low permeability. Good understanding of the geomechanical properties is essential for reducing potential hazards and enhancing the design of the HF programs. Basic geomechanical properties of Montney shale, like Young’s modulus, Poisson’s ratio, uniaxial strength, cohesion and friction angle, have been reported by several researches. However, few results about the fracture behavior can be found in the literature. This paper presents the Mode I and Mode II fracture toughness (K_Ic and K_IIc) of Montney shale. The material properties could be used for further analysis and numerical simulation. K_Ic and K_IIc are measured using the semi-circular bending method (SCB) and double shear method (DS), respectively. The SCB sample is a semi-circular disk with an edge notch throughout the sample thickness while cylindrical sample with two sets of notches on the top and bottom is used in the double shear test (DS). Confining pressure up to 50 MPa is applied to the DS sample to ensure Mode II failure. The result shows K_IIc increases nonlinearly with pressure up to 30 MPa until an upper limit is approached.