Directionless fracture stability assessment based on a 4D geomechanical model of a SAGD scenario

Abstract

In SAGD operations the injection of steam leads to thermally induced stresses and pore pressure changes in the subsurface. Although the pressure and temperature can be modelled with reservoir simulators, the change of the stress field in relation to these properties can impact the stability of faults and fractures, which in turn have effects on the fluid transport properties. To assess the potential for fault and fracture (re-)activation we create a model of a SAGD operation by coupling the outcome of a reservoir simulation to a 4D geomechanical finite-element model. The model reveals the bounding faults to have critically stressed. A second, more conservative, approach uses a directionless assessment without the need of discrete fractures. It shows extensive critically-stressed regions above and below the injection at much earlier stages, which extend far into the cap-rock. The model shows the importance of creating integrated 3D or 4D models honouring overburden stiffness and vertical load in the same way as the locally induced stresses. A challenge remains in quantifying the input rock parameters for the entire vertical column. The outcome of the model stresses the need for a detailed discussion of the cap rock thickness and the impact of potential of fractures.