增强地热系统热储层-盐水-CO_2相互作用

增强型地热系统(EGS)是采用人工形成地热储层的方法,从低渗透性岩体中经济地采出深层热能的人工地热系统。以CO2为载热流体的增强地热能系统(CO2-EGS)是实现CO2减排和深部地热资源开发的有效手段,系统运行时的水-岩-气相互作用对热储层孔渗特征有着重要影响,最终会影响储层的产热能力。笔者利用高温高压反应釜模拟CO2-EGS高温下的热储层-盐水-CO2的相互作用,通过对实验中反应液离子成分变化和岩样扫描电镜进行分析,结果表明:实验后的钾长石和方解石出现溶解现象,且方解石溶蚀剧烈;岩样表面出现极少量次生方解石和钠长石,并有新矿物析出,其主要组成元素为C、O、Si、Fe,为菱铁矿的中间产物。通过TOUGHREACT建立反应性溶质运移模型,模拟上述实验的化学反应过程,模拟结果和实验数据拟合较好。该研究可为CO2-EGS的水-岩-气作用机制提供地球化学数据。

Interaction of Rock-Brine-Supercritical CO2 in CO2 EGS Reservoir

Enhanced geothermal system (EGS) is an engineered reservoir that has been created to extract economical amounts of heat from geothermal resources with low permeability and/or porosity . CO2 enhanced geothermal system is a technology of geological storage of carbon with geothermal energy development .When the supercritical CO2 is injected into a deep reservoir ,the surrounding rock will be dissolved or precipitated , and the porosity and permeability of the rock will also be changed . The interaction of rock‐brine‐supercritical CO2 in CO2‐EGS was simulated by high‐temperature & pressure reactor .The changes of ion compositions in the solution and scanning electron microscope of rock core showed that K‐feldspar and calcite dissolved after the experiment ,especially dissolution of calcite is too strong to be saturated .Meanwhile a very small amount of secondary calcite and albite were generated , with the generation of a new kind of mineral which is likely to be the intermediate product of siderite composed of C ,O ,Si ,and Fe .The chemical reactions in the experiments were simulated by reactive transport modelling using TOUGHREACT . The information currently available by numerical simulations is generally consistent with the results from the laboratory experiment .This study provided geochemical evidences for chemical interaction mechanisms in CO2‐EGS .