CO₂ injection and storage in geological reservoirs is an attractive prospect for mitigating the anthropogenic production of greenhouse gases and global warming. The technology could lead to mineral precipitation and therefore stable storage over geological time scales. This contribution investigates the evolution of three calcite-rich reservoir rock analogues during injection of and exposure to supercritical CO₂ (scCO₂), i.e., two limestones (Tuffeau and Savonnieres) and a synthetic calcite-cemented sandstone (CIPS). Three types of exposure protocols have been conducted: (i) scCO₂ injection and a four-hour residence time in an initially dry rock; (ii) scCO₂ injection and a two-hour residence time in an initially brine-saturated rock; and (iii) scCO₂ injection and a four-hour residence time in an initially brine-saturated rock. Two aspects are monitored during these experiments: (i) the evolution of the pore fluid chemical composition; and (ii) the evolution of the rocks’ physical properties (i.e. porosity, permeability, P-wave velocity and electrical resistivity). Additionally, some scCO₂ injection and exposure experiments in the brine-saturated rocks have been conducted using X-ray tomographic monitoring.

X-ray tomographic monitoring suggests that scCO₂ first displaces the water, leading to an average water saturation of about 70–90%. Then, scCO₂ dissolves in the pore brine, leading to a homogeneous decrease by about 3% in water saturation of the sample. As a result, the pore brine acidifies even after 2 h of exposure only, which leads to calcite dissolution and a significant increase in the brine’s concentration in calcium cations. For the samples and most exposure experiments, evidence of calcite dissolution is inferred from the measured physical properties. For the brine-saturated Tuffeau limestone and CIPS sandstone, calcite dissolution leads to significant mechanical weakening. For the brine-saturated Savonnieres limestone, the sample subject to two-hour residence time shows evidence of calcite dissolution, whereas the sample after four-hour residence time does not. Calcite re-precipitation could be the cause of this unexpected response after four hours.

将CO ₂注入和储存在地质储层中对于减少人为产生的温室气体和全球变暖具有诱人的前景。该技术可能导致矿物沉淀，因此在地质时间范围内稳定储存。这项研究调查了在注入和暴露于超临界CO ₂（scCO ₂）期间三种富含方解石的储集岩类似物的演化，即两种石灰岩（Tuffeau和Savonnieres）和一种合成方解石胶结砂岩（CIPS）。已经进行了三种类型的暴露方案：（i）scCO ₂注入和在最初干燥的岩石中有四个小时的停留时间；（ii）scCO ₂在最初充满盐水的岩石中注入和两个小时的停留时间；（iii）scCO ₂注入和在最初被盐水饱和的岩石中停留四个小时的时间。在这些实验中监测了两个方面：（i）孔隙流体化学成分的演变；（ii）岩石物理特性（即孔隙度，渗透率，P波速度和电阻率）的演变。此外，已经使用X射线断层扫描监测在盐水饱和的岩石中进行了一些scCO ₂注入和暴露实验。

X射线断层扫描监测表明，scCO ₂首先取代了水，导致平均水饱和度约为70–90％。然后，scCO ₂溶解在孔隙盐水中，导致样品的水饱和度均匀降低约3％。结果，即使仅暴露2小时，孔隙盐水也会酸化，这导致方解石溶解，盐水中钙阳离子的浓度显着增加。对于样品和大多数暴露实验，从测量的物理性质可以推断出方解石溶解的证据。对于盐水饱和的Tuffeau石灰岩和CIPS砂岩，方解石溶解会导致机械强度显着降低。对于盐水饱和的Savonnieres石灰石，经过两小时停留时间的样品显示出方解石溶解的迹象，而经过四小时停留时间的样品则没有。四小时后方解石再沉淀可能是这种意外反应的原因。