Experimental investigation of hydraulic fracture growth in an anisotropic rock with pre-existing discontinuities under different propagation regimes

Laboratory experiments have been carried out to investigate the growth of hydraulic fracture (HF) in an anisotropic rock with pre-existing discontinuities such as bedding planes and veins. The experiments are designed in light of scaling relationships that enable investigation on the impact by the weak mechanical discontinuities on the HF growth under desired regimes (under either a toughness dominated or a lag-viscosity dominated regime based on the scaling analysis). According to our laboratory observations, planar HF growth is promoted in the experiments under the lag-viscosity regime, in which the radial HF is able to cross both the bedding planes and veins. In contrast, profound influence of the weak discontinuities is shown in the toughness dominated experiments, causing the HF to be diverted into, or arrested by the pre-existing weak planes. The test results suggest that the complexity of the fracture path is highly dependent on a dimensionless toughness, K_m. This laboratory study highlights the importance of the hydromechanical characteristics in the HF propagation in anisotropic rocks with pre-existing weak discontinuities.