Progress of basic theories and technologies of safety pre-control in the in-situ pyrolysis of oil-rich coal

Against the backdrop of escalating global energy crises and driven by the national strategic imperative to enhance domestic oil and gas supply, in-situ pyrolysis technology for oil-rich coal has garnered unprecedented attention in China due to its advantages of lower pollution, minimal geological disturbance, and high potential for large-scale deployment. Nevertheless, the inherent challenges of drilling-based in-situ pyrolysis including non-visualized processes, personnel inaccessibility, and complex subsurface reaction conditions, pose significant safety risks to coal production, constituting critical constraints for large-scale technological deployment. A comprehensive understanding of oil/gas production characteristics and their combustion/explosion hazards, the regulation mechanisms of the in-situ pyrolysis reactions, the fracture propagation laws during pyrolysis, the oil/gas migration mechanisms, as well as the environmental impacts and corresponding prevention/control technologies, forms the essential foundation for ensuring stable operation and safety risk mitigation in in-situ pyrolysis of oil-rich coal. Nevertheless, key knowledge gaps persist: The characteristics of oil/gas production and their associated combustion/explosion risks remain unclear; The heat transfer laws and transport models within the pyrolysis zone are inadequate; and the migration patterns of oil/gas products under multi-field coupling effects are not yet fully elucidated. Building upon the refinement of these fundamental theories, the development of fracture-sealing materials capable of simultaneously preventing gas escape and stabilizing overlying strata, the exploration of sealing techniques for discontinuous fracture spaces, the invention of shielding/isolation technologies for pyrolysis reaction chambers, the advancement of an integrated air-space-ground multi-dimensional monitoring system with efficient data collection and processing, and the establishment of an intelligent and automated control system for the in-situ pyrolysis reaction are crucial for providing safety assurances for the technology's promotion. Although relevant theoretical, technological, and equipment research has been conducted globally, it has not yet fully addressed the pre-control safety requirements of the in-situ pyrolysis process for oil-rich coal.