Low Salinity Polymer (LSP) injection is a promising hybrid enhanced oil recovery (EOR) technique with immense synergistic advantages in improving injectivity, displacement efficiency, sweep efficiency, polymer rheology, and polymer viscoelasticity. To model the LSP injection, the Polymer-Brine-Rock (PBR) interactions must be precisely captured at core-scale and further upscaled to field-scale predictive model. Also, although the literature has many experimental and theoretical studies on LSP floods, few of these works address the industry's experience with LSP-based EOR at field-scale applications. Therefore, moving from experimental laboratory study to field-scale predictive modeling is an enormous challenge. This contribution describes a pertinent reservoir simulation analysis of an LSP-based EOR method from core-to-field scale. This work employs a proposed MATLAB-Reservoir-Simulation Toolbox (MRST) flow model to gain an in-depth understanding of LSP techniques at the field-scale. This proposed MRST simulator captures the physico-chemical aspects of the LSP flooding, including inaccessible pore volume (IPV), polymer rheology, permeability reduction, and the effects of shear rate and salinity. After successful implementation and validation of the proposed MRST simulator to predict LSP performance at the core scale, field-scale simulations were used to assess LSP injection in a quarter 5-spot well pattern. To identify the optimal LSP injection scenario on oil recovery and oil residual saturation, we carried out a sensitivity analysis by varying the injected water salinity, polymer concentration, and injection scheme.
The field-scale simulation results revealed the positive effect of injection polymer concentration on polymer viscosity, and thus, oil displacement efficiency. Likewise, tertiary polymer flooding may increase volumetric sweep efficiency by reducing gravity underride and sweeping top layers. Also, tertiary low salinity polymer (LSP) flooding might lead to an additional 11% oil recovery OOIP since it would increase both the microscopic and macroscopic sweep efficiencies. Furthermore, the effect of polymer concentration was not much pronounced compared to the effect of water chemistry (i.e., salinity) on oil recovery and remaining oil saturation. Nonetheless, it is thought that polymer concentration may be one of the key parameters significantly boosting sweep efficiency and oil recovery in reservoirs with more viscous oil. Finally, starting early with LSP flooding in the secondary stage improve oil recovery while yielding higher benefits for environmental and economic advantages. The findings of this study suggest that significant attention must be provided to the selection of water salinity, polymer concentrations, and the adjustment of injection strategies for successful LSP flooding in harsh conditioned carbonate reservoirs.
