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

Abstract

Abstract Carbon dioxide enhanced oil recovery (CO 2 -EOR) offers dual benefits of increasing hydrocarbon production and sequestering anthropogenic CO 2 ; however, conventional CO 2 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 CO 2 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), CO 2 flooding alone, polymer flooding alone, polymer (1.5 g/L) followed by CO 2 , and CO 2 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). CO 2 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 CO 2 achieved 89.3% OOIP, while CO 2 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 CO 2 flooding alone. The combined polymer-CO 2 flooding system delivers superior oil recovery compared with individual processes. The optimal strategy-CO 2 injection followed by 1.5 g/L xanthan gum polymer-maximizes both microscopic displacement efficiency (CO 2 -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.