A Mathematical Improvement to SAGD Using Geomechanical Modelling

Steam assisted gravity drainage (SAGD) is a thermal oil recovery technique which has been used mostly for Alberta's unconventional oil sands reservoirs. Roger Butler, known as the father of SAGD, was the first one to establish a theory and an analytical model for SAGD. His model is a rigorous solution and is widely referred to as a SAGD fast flow simulator. However, geomechanics, which has been shown to be a relevant part of SAGD's physics, has not been included in the model. When rock properties are influenced by geomechanical behaviour, the Butler theory is not able to capture the complete physics of the SAGD process. In such cases, the model must adopt unrealistic or high values for rock properties. In this study, a classical theory in the field of geotechnical engineering (limit equilibrium) is employed to act as the geomechanical module for SAGD's mathematical coupled simulation. The Butler/Reis model has also been improved using a model of slices for flow simulation. Methodology of combining these two models in a single coupled mathematical simulator is presented in this paper. The solver is a fast and realistic proxy and can be used as a low-order tool for history matching. The results of coupled simulations show that the model is able to predict permeability and porosity of the reservoir closer to real values than uncoupled (flow only) modelling.