Aquathermolysis Gas Generation in Thermal Recovery: A Review and Perspectives on Mechanisms, Modeling, Simulation, and Challenges

Significant production of associated gas during steam assisted gravity drainage (SAGD) operations in heavy oil reservoirs has drawn increasing attention due to its substantial influence on reservoir temperature distribution, steam chamber development, and overall recovery performance. Notably, observations from the Du-84 block in Liaohe’s Guantao formation have reported substantial associated gas output (∼11×104 m3/day), directly linked to aquathermolysis reactions. Despite extensive research using laboratory experiments, kinetic modeling, and numerical simulations, an integrated understanding that links gas generation mechanisms to practical reservoir management remains elusive. This review systematically synthesizes current knowledge of mechanisms of associated-gas generation during heavy-oil aquathermolysis, emphasizing recent experimental findings, existing kinetic models, and reservoir simulation practices. The key contribution of this review is providing a comprehensive framework that integrates mechanisms, modeling, and simulation for aquathermolysis gas generation (AQGG), aiming to guide future research and field applications. Particular attention is given to how the distribution of these gases affects reservoir performance, particularly oil production and steam consumption in steam-based processes. We highlight the urgent need for more comprehensive and integrative kinetic models that accurately describe gas-composition variations and their implications for reservoir performance. Existing studies predominantly focus on acid gases (CO2 and H2S), neglecting detailed characterization and implications of hydrocarbon gases and other noncondensable gases. Ultimately, this review identifies critical gaps in current research and advocates advancing modeling and simulation approaches to better translate experimental insights into practical reservoir applications, thereby enhancing SAGD efficiency and enabling more effective reservoir management strategies.