Research Progress on Supercritical CO2 Thickeners
According to the thickening principle and molecular structure of thickeners, supercritical carbon dioxide (sc-CO2) thickeners were summarized and introduced by dividing into polymers, small molecular compounds, and surfactants. The properties such as solubility, thickening effect, thickening condition, and existing problems of sc-CO2 thickeners are analyzed and assessed, and the research progress and future prospects of sc-CO2 thickeners are proposed. Sc-CO2 is used in both CO2 fracturing and CO2 flooding for enhanced oil recovery (EOR). However, due to its low viscosity, the proppant carrying ability and filtration control ability of sc-CO2 are too weak to fracturing, and it exacerbates gravity override of the CO2 and it induces an unfavorable mobility ratio that results in viscous fingering, early breakthrough, poor sweep efficiency during CO2 flooding. Thus sc-CO2 thickeners have a good application prospect in oil and gas production for improved oil recovery (IOR).