Thermally induced deformation and failure in shale under drained and undrained heating

Abstract

The clay shale is subjected to high pressures up to 10 MPa and high temperatures up to 300 °C during the recovery process. Very few experimental researches have been conducted to investigate the thermal response of clay shale under such environment. In this paper, the thermal responses of clay shale under different heating rate conditions are investigated by applying X-ray CT scanning. Under drained condition with a slow heating rate, the deformation behavior is the combined effect from the thermal expansion of the solid particle and the thermal dehydration of Stern layer in clay particles. The thermally induced contraction is significant when the thermal dehydration in clay particles dominates the deformation. The thermally induced contraction behavior is more significant in the axial direction (normal to the bedding plane) than that in the radial direction (parallel to the bedding plane) of the shale sample due to the intrinsic oriented fabric. Under fast heating condition, the thermally induced pore pressure generates the failure behavior since the thermal expansion coefficient of water is much higher than that of solid grain in shale.