Research Progress on CO₂ Pre-Fracturing Technology in Unconventional Reservoirs

The advancement of fracturing technologies in unconventional reservoirs plays a crucial role in the efficient and environmentally friendly development of unconventional hydrocarbon resources. Traditional hydraulic fracturing faces challenges such as high water consumption and reservoir damage, which limit its applicability in specific reservoirs. CO₂ pre-pad fracturing technology, as an innovative water-free fracturing technique, has shown promising potential in the development of unconventional oil and gas reservoirs. Through a systematic review of domestic and international literature on CO₂ pre-fracturing technology, in-depth research was conducted in this study focusing on aspects such as the fracturing mechanism of CO₂ pre-fracturing, process optimization, CO₂-rock-crude oil interaction mechanism, fracture propagation law, and field applications. Emphasis was placed on analyzing the characteristics of CO₂ during fracture initiation, propagation, and its interaction with crude oil, as well as the influences of key factors—including natural fracture distribution, CO₂ injection rate, in-situ stress field, and reservoir lithology—on the CO₂ fracturing effect. It has been demonstrated that natural fractures, in-situ stress conditions, and injection rate are the key factors controlling fracture propagation morphology and the stimulated reservoir volume. Once injected into the reservoir, CO₂ interacts with the rock through physicochemical processes, whereby the mechanical strength of the rock is reduced, fracture propagation is further facilitated, and efficient hydrocarbon flow channels are generated. In shale oil, tight oil, and heavy oil reservoirs, significant production enhancement has been achieved by CO₂ pre-pad fracturing; however, its applicability mechanisms and optimization design methods remain to be systematically investigated. The current status of CO₂ pre-pad fracturing technology in unconventional reservoir development is summarized, and future research directions for CO₂ pre-pad fracturing are proposed.