Laboratory Investigation and Simulation Modeling of Polymer Flooding in High-Temperature, High-Salinity Carbonate Reservoirs

Polymer flooding is one of the most commonly employed improved oil-recovery techniques. However, its successful application is related to favorable reservoir conditions and geology. In addition, its application in high-temperature, high-salinity (HT-HS) carbonate reservoirs is still a challenging task. A series of laboratory core-flood experiments have been performed at reservoir conditions (temperature of 120 °C and salinity of 167 g/L) on carbonate outcrop core samples to evaluate the flow behavior of polymer injection. A baseline with continuous polymer injection is established initially, and the experimental data are then history-matched to generate the relative permeability curves for the process using commercial software. Various parameters including reservoir permeability, polymer-slug size, polymer initiation time, and flow rate are varied to determine the optimum flooding conditions. All of the simulation results are then revalidated with the experimental results. Encouraging results are obtained at the optimum conditions despite the mechanical degradation of the polymer, which shows up to 85% recovery of the original oil in place with manageable polymer adsorption on the rock surface. It is also observed that the potential polymer can work effectively on the core samples having moderate (30 mD) to high-permeability samples; however, the polymer loses its efficiency in lower-permeability rock samples. The results also indicate that early polymer injection helps to reduce the polymer-slug size required to reach residual oil saturation. The optimum conditions for polymer-slug size and polymer initiation time is 0.1 pore volume after 0.3 pore volume of water injection, respectively. The smaller polymer-slug size also helped to manage the resistance factor and the residual resistance values in the desirable range, i.e., 1.9 and 1.1, respectively. Identifying a polymer that can withstand high-temperature and high-salinity conditions in carbonate reservoirs will be a major step toward broadening the scope of successful polymer-flooding applications.