盐水层CO_2埋存时岩石流体综合作用及对选址影响

Rock-Fluid Interactions and their Effects on Site Selection of CO_2 Storage in Saline Aquifer

为研究盐水层CO_2埋存过程中,CO_2注入导致的岩石流体作用对储层物性和CO_2注入性的影响,将地层水蒸发盐析与地化反应进行耦合,建立了盐水层CO_2埋存反应流动综合模型。利用该模型,分析了流体流动规律、矿物溶解/沉淀和盐析,并对储层物性进行了敏感性研究。模拟结果表明,沿CO_2运移方向,储层分为干涸区(纯CO_2渗流区)、气液两相渗流区和CO_2溶解区三个区域。盐析主要发生在干涸区域,地化反应导致的矿物溶解/沉淀反应则主要发生在气液两相渗流区和CO_2溶解区。地化反应导致的矿物溶解/沉淀分布范围大,但其变化量较小,施工阶段可忽略其对注入性的影响。而受地层水回流影响,大量NaCl被地层水携带至干涸区域前缘处析出,造成储层孔隙度和渗透率严重下降,使得盐析对CO_2注入性影响远大于矿物溶解/沉淀的影响。注入速率、地层水盐度和初始渗透率对岩盐析分布影响较大,CO_2埋存选址时,应选择合适的盐水层降低岩石流体作用对注入性的影响。

In order to study rock-fluid interactions and their effects on reservoir physical properties and injectivity during CO2 geological storage, a comprehensive reaction transport model was established by coupling salt precipitation and geochemical reactions. Effects of fluid flow, mineral dissolution/precipitation and salt precipitation on reservoir physical properties were studied by sensitivity analysis. Simulation results show that the reservoir can be divided into three zones along with CO2 migration, which are dry-out zone（i.e.CO2 only）, gas-liquid two-phase seepage zone and single aqueous phase zone with dissolved CO2. Salt precipitation mainly occurs in the dry-out zone, and mineral dissolution/precipitation caused by geochemical reactions mainly occurs in the gas-liquid two-phase seepage zone and single aqueous phase zone. Mineral dissolution/precipitation happens in large areas but with little variation during CO2 injection. Therefore, its effect on reservoir physical properties can be neglected during injection. Back flow of formation water results in large amount of Na Cl moving towards the edge of the drying zone, which precipitates in that zone and seriously damages reservoir porosity and permeability. Therefore, salt precipitation has significant effects on the reservoir physical properties and CO2 injectivity. Factors including injection rate, salinity, and permeability show great effects on salt precipitation, and saline aquifer with moderate injection rate, salinity, and permeability should be considered for CO2 geological storage.