A Coupled Geochemical-Based Modeling Approach for Low Salinity Polymer (LSP) Injection: Effects of Salinity, Rock-Type, and Temperature on Polymer Rheology

The hybrid low-salinity polymer (LSP) injection technique has potential for significant synergistic advantages as an enhanced oil recovery (EOR) approach. Previous studies indicated that LSP-injection appreciably improves polymer rheology, injectivity, viscoelasticity, and displacement efficiency. However, effectively modeling of LSP injection is still lacking and necessitates realistic simulation of polymer-brine-rock (PBR) interactions in a mechanistic predictive model. In this study, the MATLAB Reservoir Simulation Toolbox (MRST) coupled with IPhreeqc geochemical software is used to gather deeper understandings of the PBR interactions during LSP-injection. This contribution relates to the sensitivity analysis performed to investigate the effects of salinity, rock-type, and temperature on polymer viscosity during LSP process. Additionally, the de-risking step involving the charge ratio (CR) analysis is considered to estimate the potential polymer viscosity loss for various salinities, rock-compositions, and temperatures. The inaccessible pore volume (IPV), Todd-Longstaff mixing model parameters, polymer adsorption, permeability reduction as well as salinity and shear rate effects on polymer viscosity were modeled via the coupled MRST-IPhreeqc simulator. The results showed that 6-times spiked salinity (3,738 ppm) scenario is more preferable than 6-times diluted salinity (103 ppm) scenario with corresponding viscosity losses of 53% and 56%. Also, the anhydrite mineral showed the highest viscosity loss of 60% among other rock-forming minerals, followed by dolomite of 56%, and lastly, calcite with the lowest viscosity loss of 50%. For the temperature effect, the highest viscosity loss of 59% was observed at 25°C, whereas the 90°C-temperature model is the most advantageous with lowest viscosity losses of 48%. For LSP injection de-risking measures, the divalent-cation's effect was correlated with the CR value. Consequently, it is crucial to get an optimal CR value at which viscosity loss is minimum. Based on the CR analysis, a CR > 1 suggests negligible viscosity loss in the LSP-solution, which in this study correlates to the cation threshold concentration of 130 ppm. A CR < 0.35 is expected to result in substantial viscosity loss for the LSP solution. When 0.35 < CR < 1, additional risk-analysis of polymer viscosity loss in the LSP solution is required. This contribution could also help bolster further studies and eventually aid more efficient LSP-injection designs.