CO2在盐水层中的扩散和运移泄漏风险评价模型

温室效应和空气污染是21世纪人类面临的严重问题,而CO2埋存是解决温室效应的最有效方法。在CO2地下地质埋存中,盐水层埋存因其地质储量巨大受到了极大关注,同时也存在很多潜在的风险,因此建立CO2注入到盐水层后的扩散运移泄露风险评价模型将为人类安全埋存CO2提供理论支持。首先,考虑到CO2在联通水层中因浓度差泄漏,以菲克定律为理论基础,结合惠尔凯公式,建立了CO2扩散泄漏风险评价模型;其次,考虑到CO2在联通水层中因压力差泄漏,以达西定律为基础,利用气体平面径向稳定渗流公式和垂直管流相关公式等建立了CO2运移泄露风险评价模型;最后,考虑到CO2从盖层逃逸,以毛细管压力为基础建立了CO2通过盖层泄漏风险评价模型。结果表明,扩散系数越大,泄漏时间越短;扩散和运移泄漏时间相差很大,计算运移泄漏时可忽略扩散作用的影响;当埋存的CO2剩余压力小于盖层的突破毛细管压力时,气体以扩散方式泄漏,否则在压力差的作用下以渗流运移方式泄漏。

A Model of Diffusion and Migration Leakage Risk Assessment of CO_2 in Saline Aquifer

Serious problems in the 21st century are the greenhouse effect and the air pollution,and CO2 storage is the most effective way of solving the greenhouse effect.In underground geological CO2 storage,saline aquifers has attracted considerable attention for its huge storage capacity,but there are many potential risks,thus establishing CO2 diffusion and migration leakage risk assessment model in the saline aquifers can provide theoretical support for safe storage.Firstly,CO2 diffusion leakage risk assessment model is established considering CO2 leakage risk in the connected aquifers due to concentration difference based on Fick ’ s law as the theoretical basis and combined with the Wheelke formula.Secondly,CO2 migration leakage risk assessment model is established considering CO2 leakage in the connected aquifers because of pressure difference based on Darcy’ s law and using gas plane radial steady seepage formulas and related formulas of vertical pipe flow.Finally,CO2 leakage risk assessment model through the caprocks is established considering CO2 escaping from the caprocks based on capillary pressure.The results show that the leakage time is shorter as the increase of diffusion coefficient;diffusion time and migration leakage time varied widely,and diffusion effect can be ignored when the migration leakage time is calculated;if the residual pressure of the stored CO2 is less than the breakthrough capillary pressure of the caprocks,the gas will be diffusion leakage,otherwise,the gas will be seepage migration leakage under the effect of the pressure difference.