地质封存过程中CO2泄漏途径及风险分析

CO₂捕集和地质封存可望成为减少温室气体排放的重要且有效的方法，但其安全性一直受到广泛关注。在研究各种CO₂地质封存体及其圈闭机理的基础上，根据不同封存体中潜在的泄漏途径及主控因素，结合实例对可能的CO₂泄漏进行了描述和相应的风险分析。研究结果表明，枯竭油气藏的地质封闭性已得到证实，井的失效将是CO₂泄漏的主要途径。通过与提高油气采收率技术相结合，在油气藏中封存CO₂具有一定的经济性，但由于油气田分布不广，封存潜力有限，仅适合于中短期的CO₂处置。深部盐水层分布较广，可选择的圈闭和封存机理较多，泄漏途径和未知因素也较多，泄漏风险较高，但封存潜力巨大，是最具前景的CO₂封存体。煤层通过吸附可达到封存CO₂的目的，但其圈闭机理单一，对煤层压力的依附性较大，且影响未来煤资源的利用，其安全性和经济性相对较差。海底水合物封存方案具有热力学可行性，但海底水合物层埋深浅，地质圈闭性差，CO₂泄漏风险较高，其封存和泄漏机理以及CO₂注入方法有待进一步研究和关注。

Leakage pathways and risk analysis of carbon dioxide in geological storage

Geological storage of CO₂ technologies has become an important and effective method for reducing the emission of greenhouse gases, while its safety in terms of CO₂ leakage has always been an eminent issue for concerns. In this paper, the trapping and sequestration mechanisms of CO₂ in various geological structures are described, and the potential pathways for CO₂ leakage and the related control factors on leakage risks are analyzed and assessed based on case studies and review of the literature. The geological structures analyzed in the paper include depleted oil and gas reservoirs, deep saline aquifers, coal seams and offshore hydrate-bearing sediments. Storage of CO₂ in depleted oil and gas reservoirs has the highest confidence in safety,though the failure of wellbore may cause CO₂ leakage, but their gas sealing capability has been proven during the trapping of oil and natural gas, and it can provide an economic bonus if CO₂ EOR process is considered. This scheme can be adopted for CO₂ disposal in short and medium terms because the storage potential of available oil and gas reservoirs is limited. The storage in saline aquifers involves many trapping mechanisms; therefore there are many potential pathways for CO₂ leakage and unknown factors, leading to relatively high risk of leakage. But due to wide distribution of saline aquifers and their enormous storage potentials, this scheme can be the most promising method for CO₂ sequestration in future. The trapping mechanism of CO₂ in coal seams is mainly dependent on gas adsorption, which is sensitive to the variation of hydrostatic pressure in coal bed, and may result in desorption and gas leakage if it is disturbed during coal mining operations, imposing a relatively high leakage risk. The storage of CO₂ in coal seams can also affect the future use of the coal resource. The storage of CO₂ in offshore hydrate-bearing sediments is thermodynamically feasible, but due to the shallow burial depth and lack of geological trapping, it may pose a high risk for leakage. The injection of CO₂ into the hydrate stability zone is also difficult, so this scheme needs further study and concerns.