COUPLED GEOMECHANICAL-THERMAL SIMULATION FOR DEFORMING HEAVY-OIL RESERVOIRS

The paper describes a novel numerical model for the solution of poro-e lasto-plasticity and multiphase, thermal flow in unconsolidated heavy- oil and oil-sand reservoirs. The elasto-plastic deformation is calcula ted using a finite-element incremental plasticity model with Mohr-Coul omb and Drucker-Prager as the yield criteria. This model is coupled wi th CMG's thermal simulator STARS which is capable of handling many adv anced thermal recovery processes. The geomechanical calculation is in fact an effective stress analysis which solves a set of force balance (equilibrium) equations based on total stresses. These are augmented b y the elastic material behaviours, plastic yield criteria, plastic flo w rule, work-hardening law, and the strain-displacement relationships. Besides volumetric deformation, the solution gives the displacements in each direction, stresses, and strain distribution in the reservoir. The behaviours of reservoir multiphase flow and heat transfer process es are most significantly affected by the volume change and the associ ated permeability increase. The volume change is calculated by the pla sticity model, whereas the permeability increase is related to the vol ume change via tabular data. The prediction of shear failure region, t he rotation of principal stress axis, and the reduction of effective s tresses as a result of pore pressure increase, are all important pheno mena affecting the placement of fluid and heat in the formation.