Effect of Water Saturation on Failure Behaviour of Mudstones under High Pressures

Water as pore fluid is an important factor that influence rock deformation and failure behaviour. This paper presents an experimental study on the effects of water saturation on the failure behaviour of mudstones at high confining pressures. Triaxial compression experiments were performed at confining pressures up to 130 MPa, on dry and water-saturated mudstone samples. Results including stress-strain curves, failure strength, and failure modes, showed that the mudstones experienced brittle, brittle-ductile transition, and ductile failure behaviour as the confining pressure increases. The results also revealed that water significantly weakened the rock, thereby reducing the failure strength and causing the rock to become ductile at lower confining pressure compare to dry conditions. Furthermore, in water-saturated conditions, the brittle-ductile transition behaviour is accompanied by shear band fractures and ductile flow, as opposed to shear fractures to shear band fractures in dry conditions. The findings of this study could provide valuable information for optimizing hydraulic fracturing techniques and improving production efficiency in unconventional oil and gas reservoirs by identifying the conditions and depths of the transition from brittle to ductile failure behavior.