Creep Behaviour of Shale at Elevated Pressure and Temperature Conditions

In order to estimate the fracture healing rate of hydraulically induced (propped) fractures in shale reservoirs, knowledge of the long-term creep properties of shales are required. We performed deformation experiments on a low maturity, porous and carbonate-rich Posidonia oil shale using a high temperature, high pressure deformation apparatus. Constant load (creep) tests were done at temperatures between 50° and 200°C and confining pressures of 50–150 MPa. All samples deformed in the semibrittle regime showing transient creep behaviour, partially associated with porosity reduction. Creep rates were clearly enhanced at high differential stress, high temperature and low pressure. Extrapolation of creep rates measured in the laboratory to in-situ conditions has to take into account these combined effects to obtain reliable results.