Application of Thickeners in Supercritical Carbon Dioxide EOR and Fracturing: A Review

Supercritical carbon dioxide (SC-CO2) exhibits many advantages in the oil field, such as the facile creation of complex fractures, the mitigation of water sensitivity issues, and enhanced backflow efficiency. Nevertheless, the low viscosity of SC-CO2 significantly impacts the production enhancement from CO2 EOR and fracturing, limiting its widespread application. Therefore, the investigation of thickeners in SC-CO2 and the design of clean and efficient SC-CO2 thickeners are pivotal for advancing the CO2 EOR and fracturing technology. This article elucidates the mechanisms behind SC-CO2 thickening agents. Effective thickeners possess exceptional solubility and can establish spatial network structures through molecular aggregation or interactions between compounds, thereby restricting the movement of carbon dioxide molecules to achieve thickening. The article explores various supercritical CO2 thickening techniques. The results indicate that supercritical CO2 thickening technologies can effectively control the CO2 flow, prevent the occurrence of viscous fingering phenomena, and enhance the sand-carrying capability of fracturing fluids, ultimately improving unconventional reservoir recovery rates. However, existing thickeners still suffer from limitations in thickening capacity, the need for significant cosolvents, and potential reservoir damage. Therefore, it is imperative to further enhance the performance of thickeners and explore the possibility of adding new nanomaterials.