Geologic carbon storage projects aim to permanently trap large volumes of CO₂ in reservoir rock sealed with low permeability layers. As high-pressure supercritical or liquid CO₂ is injected, hydromechanical and chemical processes caused by the reaction between the rock and acidic mixture of brine and CO₂ are initiated. The compressibility of reservoir rock needs to be properly characterized in order to assess the deformation and stability of the host formations, and there are a number of factors to be considered, including the matrix structure, solid, pores, and fluid. This study triggers from a fundamental question whether CO₂ treatment affects the compressibility of the rock matrix and its dominant composing solid minerals. Three different reservoir representatives are selected: Berea sandstone for silica-rich rock, and Apulian limestone and Indiana limestone for calcite-rich rock. Quartz and calcite are the main composing minerals of the reservoir rock, and their crystals are separately examined. Experimental methods are introduced for high-pressure CO₂ treatment of water-saturated materials, and measurements of the unjacketed and solid compressibilities are conducted. No change in the solid compressibility of the sandstone and quartz after CO₂ treatment is observed, whereas it increases by 18–21% for the limestones and by 15% for calcite. The latter observation is inconsistent with the ultrasonic wave velocities measurements and is believed to be due to the local dissolution of the calcite crystal surface. The results show that only the solid matrix of the limestones becomes more compressible after CO₂ treatment. Consequent microimaging and mercury intrusion porosimetry analyses allowed observations of dissolution and precipitation of calcite, and creation of new connected and non-connected pores. Finally, the changes in limestone solid compressibilities and pore structure could significantly affect the rock properties and behavior during and after CO₂ injection and should be accounted for in the reservoir models. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.

中文翻译：

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深埋 CO2 过程中岩石基质可压缩性的变化

地质碳封存项目旨在将大量 CO ₂永久捕获在用低渗透层密封的储层岩石中。当注入高压超临界或液态 CO _{2 时}，由岩石与盐水和 CO _{2 的}酸性混合物之间的反应引起的流体力学和化学过程开始。储层岩石的压缩性需要正确表征，以评估母体地层的变形和稳定性，需要考虑的因素很多，包括基质结构、固体、孔隙和流体。本研究从一个基本问题触发 CO ₂处理会影响岩石基质的可压缩性及其主要组成固体矿物。选择了三种不同的储层代表：Berea 砂岩用于富含二氧化硅的岩石，Apulian 石灰岩和印第安纳石灰岩用于富含方解石的岩石。石英和方解石是储集岩的主要组成矿物，分别对它们的晶体进行了考察。介绍了对水饱和材料进行高压 CO ₂处理的实验方法，并进行了无夹套和固体压缩率的测量。CO ₂后砂岩和石英的固体可压缩性没有变化观察到处理，而石灰岩增加了 18-21%，方解石增加了 15%。后一种观察结果与超声波速度测量结果不一致，据信是由于方解石晶体表面的局部溶解。结果表明，只有石灰石的固体基质在 CO ₂处理后变得更具可压缩性。随后的显微成像和压汞孔隙率分析允许观察方解石的溶解和沉淀，以及新的连通和非连通孔的产生。最后，石灰石固体压缩性和孔隙结构的变化会显着影响 CO ₂作用期间和之后的岩石性质和行为。注入，并应在油藏模型中加以考虑。© 2021 化学工业协会和 John Wiley & Sons, Ltd.