Research progress of thickener for supercritical carbon dioxide fracturing fluid

Compared to traditional water-based fracturing fluids, which often result in reservoir fracturing damages, water consumption, and incomplete flowback, supercritical carbon dioxide (scCO 2 ) fracturing technology has gained attention from scholars as a promising anhydrous fracturing technique. This is primarily due to its unique properties such as being waterless, causing no reservoir damages, providing an excellent energy-enhancing effect, and enabling thorough backflow. In addition to improving the recovery efficiency through CO 2 injection during fracturing, scCO 2 fracturing technology also enables CO 2 geological storage. However, the low viscosity of pure CO 2 as a fracturing fluid significantly limits its productivity enhancement effect. Therefore, the identification of a suitable thickener is necessary to increase the viscosity of supercritical CO 2 fracturing fluids, consequently enhancing their reservoir reconstruction efficiency. This paper explores and discusses four types of supercritical CO 2 thickeners, namely siloxane polymers, hydrocarbon and oxygenated hydrocarbon polymers, surfactants, and fluoropolymers, through comprehensive research conducted domestically and internationally. The solubility, thickening ability, experimental conditions, and challenges associated with scCO 2 thickeners are analyzed and evaluated. Finally, the characteristics of each type of thickener are summarized, and future research directions are proposed.