The Effect of Temperature and Pressure on the Rock Mechanical Behaviour of the Whitby Mudstone Formation, UK

Abstract

We studied the rock mechanical behaviour of the outcropping Whitby Mudstone Formation shales (Toarcian Age) under varying temperature and confining pressure conditions, focusing on strength and elastic moduli. We compared the rock mechanical properties of the Whitby shale to published data of time and depositional equivalent shales from Northern Europe and producing shales from the US. We performed uniaxial and triaxial tests in order to constrain the effect of temperature and pressure on the mechanical behaviour of the shale. We loaded the samples normal to the bedding plane under room humidity conditions. We performed uniaxial tests at room temperature and zero confining pressure, whereas we applied confining pressure in several steps up to 50 MPa and considered temperature values between 20-150°C during triaxial tests. Ultimate strength and elastic moduli are strongly influenced by mineralogy, temperature and pressure. An increase in temperature enhances the deformability, whereby the Young’s Modulus and ultimate strength decreases. With an increase in confining pressure, Young’s Modulus and ultimate strength increases, whereas the Poisson’s ratio decreases.