Geochemical Modeling of Low-Salinity Polymer Flooding for Carbonate Rocks

The demand for global energy has been increasing continuously, and the oil and gas industry is a significant supplier of energy required to meet this demand. However, the industry faces challenges due to regulatory constraints and exploration complexity, which have made it necessary to maximize oil recovery from existing fields. Enhanced oil recovery (EOR) techniques have shown great potential in increasing oil recovery from reservoirs that were produced by conventional primary and secondary recovery methods. Chemical EOR (cEOR) techniques, specifically polymer flooding (PF), have proved valuable in improving the macroscopic sweep efficiency and changing rock and fluid interactions at a reasonable technical and economic cost. To appropriately select a suitable polymer, it is essential to understand the impact of diffusion, polymer adsorption, and geochemical interactions between the polymer, brine, and rock phases. The main objective of this study is to propose a mechanistic model that captures the physicochemical aspects of polymer flow in porous media through a geochemical perspective using a coupled reservoir flow and geochemical numerical simulator [MATLAB Reservoir Simulation Toolbox (MRST)-IPhreeqc simulator] for applications in carbonate rocks. We developed a mechanistic model using MRST reservoir flow and the IPhreeqc geochemical simulator, with the MRST polymer module modified to model key parameters such as polymer viscosity, adsorption, inaccessible pore volume (IPV), residual resistance factor, hydrolysis, and shear effects. Surface complex-ation modeling from IPhreeqc was integrated to model Indiana limestone carbonate rocks and introduced a polymer species of sodium acrylamido tertiobutyl sulfonate (ATBS) polymer for interaction within the MRST simulator for low-salinity polymer (LSP) flooding paradigm. The adsorption equilibrium is captured through thermodynamic reactions and flow equations. The updated simulator was vali-dated against experimental tests for carbonate rocks. The results prove the simulator’s effectiveness in modeling the main mechanisms of LSP. This study offers insights into geochemical, reservoir flow, and adsorption in PF. The integration of geochemical factors is crucial for optimizing PF in the Middle East’s harsh carbonate reservoir conditions, enhancing regional oil recovery. Furthermore, the sensitivity analysis demonstrated that polymer concentration significantly impacts calcite dissolution, polymer adsorption, and pH changes in the produced brine, highlighting the critical role of geochemical interactions in optimizing PF strategies.