Impacts of wellbore orientation with respect to bedding inclination and injection rate on laboratory hydraulic fracturing characteristics of Lushan shale

A series of hydraulic fracturing experiments were conducted using Lushan shale cores (50 mm in diameter and 100 mm in length) to unravel the formation mechanism of fracture networks under the combined effects of wellbore type (vertical or horizontal well), wellbore orientations relative to the bedding plane (0°, 30°,45°, 60°, and 90°), bedding inclinations (0°, 30°,45°, 60°, and 90°), and injection rates (0.03, 0.3, 3, and 30 mL/min). We monitored acoustic emission and surface displacements during the test and conducted post failure inspection via a fluorescent tracer and a 3D laser scanner. We show that adjusting the maximum principal stress perpendicular to the wellbore is beneficial for reducing the breakdown pressure. Inclined bedding tends to initiate along the bedding plane with relatively low fracture initiation pressure and breakdown pressure. Deploying the wellbore inclined to bedding inclination and/or adopting a low injection rate is beneficial to reduce the shale breakdown strength and create a complex fracture network. However, this will correspondingly increase the fracture surface roughness, which may impede the effective transportation of proppant. These findings can provide an important reference for field hydraulic fracturing.