Confronted with the challenges of ever‐increasing global demand for oil and gas, coupled with the depletion of conventional resources, the strategic importance of unconventional oil and gas resources is becoming increasingly significant, with shale oil being particularly crucial. Immature to low‐maturity shale oil reserves are extremely abundant, constituting over 80% of the world’s total shale oil resources. Thus, the efficient enhancement and development of immature to low‐mature shale oil is of profound importance for ensuring future energy supplies and reshaping the global energy landscape. This review begins with an in‐depth analysis of the microscopic conversion mechanism and reaction pathway of immature to low‐maturity shale oil at the molecular structural level. Building on this foundation, it systematically summarizes and analyzes the current main in situ upgrading methods, including thermal upgrading and catalytic synergistic thermal upgrading combined with catalysts, which essentially rely on heat to drive the thermal cracking and hydrogenation reactions of organic matter. However, these methods typically encounter challenges such as high energy consumption, elevated costs, and substantial environmental impacts, which limit their widespread adoption and application. In contrast, microbial upgrading technology exhibits significant advantages by achieving upgrading through environmentally friendly and low‐energy biological processes. The primary mechanisms include direct biological conversion, where microorganisms directly metabolize organic components in shale, degrading or converting them into lighter hydrocarbons with improved mobility and lower viscosity, and indirect biological promotion, which alters the properties of reservoir rocks, thereby promoting the release of organic matter and enhancing its effective contact with the external modification environment. Although the microbial upgrading of immature shale oil remains in its foundational development stage, lacking in mechanistic and systematic research, existing studies have demonstrated progress in the application of microbial technology for shale oil extraction. This progress is achieved through the screening and optimization of microbial communities to enhance shale oil recovery rates. Consequently, this review explores the future development directions of microbial technology in the field of shale oil and gas extraction in its final section, aiming to promote the widespread application of this green and low‐carbon technology.
Liu et al. (Thu,) studied this question.