Continuous Variable Pressure Steam Injection for Enhanced Oil Recovery

Abstract

Abstract Continuous variable pressure steam injection is a new approach to manage heat flow within a reservoir and reduce the temperature of fluids arriving at producers thereby avoiding shut-in caused by high temperature. An optimal injection scenario with varied pressure and constant steam quality is shown to have the largest oil recovery given the same amount of energy injected under various reservoir settings. The economic effects were evaluated to select the optimal variable pressure injection schedule with the greatest Net Present Value (NPV). Various scenarios with different injection pressures and steam qualities were investigated and compared based upon aspects of oil recovery, energy consumption, and periods of producer shut in. Sensitivity analysis was performed regarding permeability, well distances, heat losses, as well as geomechanical model parameters including Young's Modulus, Poisson's Ratio, and initial stress. Grid refinement experiments dictated the optimal unit grid dimension for accurate 3D modeling including geological heterogeneity. Reservoir subsidence was also investigated. The variable-pressure injection cycles were designed and evaluated using an economics model. Results teach that the proposed steam injection schedules provide continuous oil production (i.e., no producer shuts in) with the largest energy efficiency and economic benefits. The hybrid injection strategy for a 3-D heterogenous case showed an increase in 15% more oil recovered compared to the constant pressure injection scenario after 10 years of production. We conclude that steam injection design effectively controls the reservoir temperature and avoids producer shut-in. The sensitivity analysis further supports the feasibility of this optimal scenario under various reservoir conditions. Inclusion of geomechanics provides important information about reservoir deformation, but geomechanics has little effect on the oil produced or the optimal injection strategy. Importantly, the subsidence results do not indicate well failure under the conditions studied. By performing a systematic investigation, the combination of continuous high and low constant-pressure steam injection for fixed time intervals yields the largest NPV.