Waterflooding significantly changes the magnitude and orientation of reservoir stresses. This paper presents the development of a new simulator that couples geomechanics with fluid flow and incorporates two-phase flow and thermo-poro-elasticity. The model is applied to water injection in typical waterflooding well patterns for both vertical and horizontal wells. The model was validated with known analytical solutions by comparing stresses, pressures and fluid saturations. The combined effect of poro- thermo-elastic stresses is shown to significantly impact injection induced fracture trajectories and, therefore, reservoir sweep efficiencies. Estimates of recovery factors, infill-well designs, well spacing and injection/production well patterns are critically affected by the reoriented stress state.
The model clearly shows that stress-reorientation during waterflooding is not a near-well phenomenon, but instead occurs on a field scale. Even for simple five-spot models, the complete reversal of the maximum and minimum horizontal stress directions can occur far from injection/production wells. The contrast between horizontal stresses also changes significantly, indicating locations where natural fracture networks are likely to be stimulated.
Stress reorientation and subsequent non-planar fracture growth is shown to be extremely important in predicting secondary and tertiary oil recovery. The simulations presented here can be used to specify well spacing and patterns to improve reservoir sweep. In-situ stresses are reoriented by the pressure, temperature, and fracture growth of different well configurations. These factors determine the direction of injection-induced fractures. Simulation results that systematically show the impact of stress reorientation on oil recovery under different reservoir and fluid conditions, as well as well patterns are presented in this paper.