A numerical and experimental approach to oil recovery performances during combined xanthan gum and carbon dioxide flooding

Abstract Carbon dioxide enhanced oil recovery (CO2-EOR) offers dual benefits of increasing hydrocarbon production and sequestering anthropogenic CO2; however, conventional CO2 flooding suffers from unfavorable mobility ratios and premature gas breakthrough, while polymer flooding alone faces challenges in high-salinity and high-temperature reservoirs. This study experimentally and numerically investigates the synergistic impact of combining xanthan gum polymer with CO2 injection to maximize oil recovery. We conducted laboratory coreflood experiments on packed sandstone (porosity 22%, permeability 1000 mD) saturated with 31°API crude oil (6.0 cP at 70 °C), testing polymer concentrations of 1.0, 1.5, 2.0, and 2.5 g/L. We evaluated five flooding scenarios: water flooding (baseline), CO2 flooding alone, polymer flooding alone, polymer (1.5 g/L) followed by CO2, and CO2 followed by polymer (1.5 g/L). We then upscaled experimental findings using CMG-IMEX reservoir simulator to field scale. Water flooding recovered 70.0% of original oil in place (OOIP). CO2 flooding alone increased recovery to 83.3% OOIP. Polymer flooding alone achieved maximum recovery of 81.3% OOIP at optimal concentration (1.5 g/L), while lower (1.0 g/L) and higher (2.5 g/L) concentrations yielded 79% and 73.5% OOIP, respectively. Sequential injection significantly outperformed single methods: polymer (1.5 g/L) followed by CO2 achieved 89.3% OOIP, while CO2 followed by polymer (1.5 g/L) achieved the highest recovery of 94.3% OOIP. An incremental gain of 24.3% over water flooding and 11.0% over CO2 flooding alone. The combined polymer-CO2 flooding system delivers superior oil recovery compared with individual processes. The optimal strategy-CO2 injection followed by 1.5 g/L xanthan gum polymer-maximizes both microscopic displacement efficiency (CO2-driven oil swelling and viscosity reduction) and macroscopic sweep efficiency (polymer-driven mobility control). This hybrid approach represents a technically viable and economically promising EOR strategy for mature sandstone reservoirs while contributing to sustainable carbon management.