废弃气藏CO2地质封存机制及运移规律研究

As energy needs around the globe are rising, simultaneously with concerns about the environmental impact of human activities, Carbon Capture and Storage has been put forward as a way to mitigate the detrimental effects of fossil fuels as an energy source.CO2 injection in the abandonment gas reservoir is effective way to come true the Greenhouse gas emissions reduction and improve the recovery factor of gas reservoir, but there are no researches on it in China are proposed. We will use the combination of physical and mathematical modeling to research. Phase behavior of different CO2-CH4-brine systems under high temperature and pressure, dissolution rule of CO2 miscellaneous gas in formation water are investigated using imported DBR-PVT tool from Canada at first. Core flooding experiment is used to research the potential of cocooning of included gas produced by capillary pressure. The chemical reaction and active mechanism between CO2 and different rocks are tested with high pressure re-actor. Core experiment is proposed to study the effect of rock salt fusion, deposition law and permeability after CO2 injection. The influence law of CO2 diffusion and movement in gas reservoir is studied. Phase equilibrium thermodynamic model for CO2-CH4-water system under high temperature and pressure, CO2 fluid-rock mineralization model and advection diffusion model are founded on the basis of experiment. Based on the models, mathematical models for multi-phase porous flow is established, in which the coupling among rock salt fusion, deposition and CO2 diffusion are taken into account. This research results, have important directive to develop physico-chemical percolation and disclose CO2 sequestration and movement law in the abandonment gas reservoir.

CO2注入废弃气藏是实现温室气体减排和提高天然气采收率双赢的有效途径。而我国还未开展该方面的研究。本项目拟采用物理模拟和数学模拟相结合的方法进行研究。首先利用加拿大进口的DBR-PVT仪开展不同组成的CO2-CH4-盐水体系在高温高压条件下的相态特征、CO2混合气体在地层水中的溶解规律研究。利用岩心驱替实验研究毛管压力产生的束缚气封存潜力；利用高压反应釜测试CO2与不同岩石矿物之间化学反应和作用机理；利用岩心实验研究CO2注入后盐岩溶解和沉积规律及其对渗流能力的影响；实验研究CO2在天然气藏中的扩散运移规律。在实验测试基础上，建立高温高压CO2-CH4-地层水相平衡热力学理论模型、CO2流体-岩石矿化反应模型和CO2扩散模型，在此基础上，建立考虑盐岩溶解和沉积以及CO2扩散耦合的多相渗流理论模型。该研究成果对于发展物理化学渗流、揭示CO2在废弃气藏中地质封存机理和运移规律具有重要意义。

碳捕集和地质封存是有效解决温室气体CO2环保问题的重要途径之一。枯竭气藏良好的封闭性和较大的储气性，以及提高采收率的双赢优势而成为CO2埋存的优势靶点。我国未来存在大量废弃边缘气藏或者低效气藏，气藏中CO2封存潜力巨大。. 本项目通过物理模拟、理论研究和应用相结合的方法，主要开展了以下研究工作：（1）利用高温高压反应釜测试HCO3-和Ca2+、Mg2+存在时，CO2在地层水中溶解度及CO2置换地层水中CH4实验，建立了高温高压CO2-CH4-地层水相平衡热力学理论模型；（2）开展了CO2-地层水-岩石的静态反应和动态驱替反应实验。通过X衍射和扫描电镜分析了PH值、岩石矿物成份和微观孔隙的变化。（3）开展了高温高压条件下CO2驱替CH4的长岩心实验，考虑了驱替速度、岩心倾角、岩心渗透率以及束缚水存在对CO2驱气及埋存效率的影响；（4）建立理论模型预测CO2注入气藏中随时间和空间变化的盐析量和盐析区域、分析孔隙度-渗透率变化关系、评价储层伤害及注入性损害程度。（5）通过考虑地层水存在气液液三相相态和数值模拟，揭示了地层水对凝析气藏CO2埋存机理影响。（6）开展了底水气藏废弃时注CO2提高采收率及埋存实例研究。. 研究结果显示：（1）修正混合参数和交互作用参数后的PR-HV模型预测CO2在高矿化度地层水中溶解度适应性更好。（2）存在黄铁矿时，CO2-岩石-地层水静态和动态反应后水中有黄色沉淀物质，渗透率降低。数值模拟也反应CO2的注入可能加剧近井带水蒸发盐析效应，使得注入能力降低。（3）地层水存在使CO2突破时间延迟，最终CH4采收率和埋存率更高，增加CO2埋存总量。（4）实例显示CO2提高CH4采收率5.8%； CO2超临界埋存占比83.78%，CO2溶解埋存占比12.67%，CO2束缚埋存量最少，仅占3.85%。（5）CO2与天然气密度差异是造成CO2流动的主要因素，CO2将倾向于向储层下部运移。该研究成果对于气藏中CO2封存及提高气藏采收率封存机理、运移规律和方案优化设计具有重要意义。