A Mini-Review of High-Temperature CO ₂ -Injection-Based In Situ Conversion in Organic-Rich Shale

Globally, vast resources of low–moderate-maturity organic-rich shale oil and gas exist, with in situ conversion technology (ICT) representing the most promising development approach. While pilot tests have achieved significant breakthroughs, fundamentally validating the feasibility of in situ conversion, challenges such as small-scale operations, marginal economics, and inconsistent performance persist. These tests commonly face technical hurdles such as low production rates, limited reservoir coverage, and formation plugging, preventing scalable commercial application. The injection of high-temperature (≥350 °C) CO2 emerges as a critical breakthrough for the low-carbon, large-scale development of these resources, offering dual benefits: it significantly enhances the thermal conformance factor and hydrocarbon recovery efficiency during in situ conversion while enabling efficient geological CO2 storage. This paper reviews the current state of ICT using high-temperature CO2 injection for low–moderate-maturity shales and the underlying multiphysics, cross-scale evolutionary mechanisms. Results demonstrate distinct advantages: the high mobility, diffusivity, and specific heat capacity of CO2 enhance heat distribution across reservoir scales; it can act as a mild oxidant, reducing the activation energy required for kerogen conversion and accelerating hydrocarbon release; it inhibits carbon deposition or condensation reactions during pyrolysis, mitigating formation plugging; and its unique displacement and miscibility effects improve the mobility of cracked products. Simultaneously, the complex pore structure created postconversion provides secure, efficient storage sites for CO2. However, the technology remains nascent, requiring extensive research to resolve key issues. Once matured, it promises to shift the development paradigm for organic-rich shales from “hydraulic fracturing production” to “in situ conversion”, synergistically boosting hydrocarbon recovery and carbon sequestration efficiency, thereby overcoming the longstanding challenge of “difficult-to-recover” low–moderate-maturity shale resources.