二氧化碳地质封存瞬时非达西流井筒泄漏模型研究

Research on Model of the Wellbore Leakage of CO_2 Geo-sequestration with Instantaneous Non-Darcy Flow Methods

二氧化碳地质封存的有效性和持久性依赖于地层的完整性,废弃井的存在是潜在的CO2逃逸路径,需要了解流体在井中的流动过程,才能确保封存的安全性。使用最近开发的TOUGH2系列软件的T2Well/ECO2N模块进行研究,此模块利用DFM模型(Drift Flux Model)考虑流体的相间滑移过程,能够更为精确地描述高速多相井流过程。笔者以我国首个CCS示范项目———神华10万吨/年CCS项目为背景,对CO2潜在的井泄漏情况进行了模拟研究,了解泄漏过程中压力和流体速度等参数的变化过程,并对系统压力、盐度(井底增加0.1MPa、1Mpa和改变储层盐度)参数进行了敏感性分析。结果表明:井筒中的流体传播速度极快,难以用达西流描述;井筒浅部出现二氧化碳的相态转变;二氧化碳的大量累积使得气体饱和度、压力、气液相流量和密度等参数出现明显波动;压力和盐度的是气液相流量和流速的敏感参数。

The efficiency and durability of CO2 storage depends on the integrity of the strata while abandoned wells are potential escape ways of CO2. With a good understanding of the flow behavior in wellbores, security of storage then can be ensure. In this paper, authors do research by using TOUGH2 codes-T2Well/ECO2N which can describe high wellbore flow accurately with the consideration of phase slip between gas and liquid. In the analong study of the well leakage of Shenhua CCS project, the variation of system parameters are recorded. The sensitivity of pressure and salinity are analyzed by increasing the pressure of well bottom and changing the system salinity. The result indicates that the phase flow in wellbore is too fast to described as Darcs/s law, the phase change appears on the upside of wellbore; COz accumulation leads to the parameters fluctuation such as gas saturation, pressure, flow rate, density and so on and pressure and salinity are sensitivity coefficient of flow rate and velocity.