Research On Integrity Evolution And Leakage Of CO₂ Geological Storage System

Injecting carbon dioxide into oil and gas reservoirs for enhanced oil and gas recovery and geological storage can not only achieve effective use of waste gas but also alleviate the greenhouse effect.It is an effective measure for energy conservation and emission reduction in the petroleum industry.Although there are many benefits to CO₂ geological storage,the risks and harms of leakage can not be ignored.This paper studies related to the integrity and leakage of carbon dioxide sequestration systems,and aims to help control the risk of leakage.The geological storage system includes a well system and a reservoir-caprock system.Its integrity is critical to ensure a long-term and safe storage,but it is difficult to maintain integrity in a carbon dioxide environment.In general,at various stages of carbon dioxide injection-transport-storage,the integrity of the storage system is gradually lost under various factors,but there is also a phenomenon contrary to conventional knowledge.Under certain conditions,the presence of carbon dioxide can make the integrity of the storage system has been increased to a certain extent,called the self-healing phenomenon of integrity,such as carbon dioxide chemical reaction induces self-healing of fractured wellbore cement permeability and rock creep to compensate for cement fractures self-healing,etc.,although the self-healing recovery of the integrity of the storage system is small,but it does reduce the risk of leakage for storage.Through the above analysis of the well-reservoir-caprock storage system in the process of CO₂ sequestration,this paper has carried out in-depth research on several aspects.The first is the study of the self-healing of the mechanical properties of the well cement in the storage system.Under the condition that the carbon dioxide has self-healing in the well cement permeability,So a simulation experiment of the mechanical properties of cracked cement under the CO₂ environment is designed.The experimental results show that the CO₂ can restore mechanical properties of the cracked well cement under certain conditions.The second is the study of the impact of carbon dioxide on the reservoir-caprock system during the injection-transportation phase.For the integrity of the reservoir-caprock system,the evaluation is made in terms of mechanical influence and chemical influence.The results show that no matter what phase of carbon dioxide is injected,it will cause mechanical failure behavior to the reservoir-caprock system,and gas-water-rock geochemical reaction will increase permeability and saturation of the formation;The third is the study of the CO₂ leakage of the geological storage system.Using TOUGHREACT software to establish a site-scale model,and based on theoretical analysis to study the CO₂leakage of caprocks,faults and cracks,and wells in the storage system.The simulation results show that the leakage of carbon dioxide is closely related to the permeability of the storage area and the interaction between different forms of leakage,Therefore,various factors should be considered and analyzed in the actual storage process.Through the combination of experiment and numerical simulation,the established objectives are completed,and the evolution law and mechanism of the integrity of the storage system are more deeply revealed.The research results will provide a basis for low-carbon emission reduction in China and provide technical support for on-site applications.