Chemo‐mechanical Alterations Induced From CO2 Injection in Carbonate‐Cemented Sandstone: An Experimental Study at 71 °C and 29 MPa.

Carbon capture, utilization, and storage may lead to mechanical degradation of the subsurface reservoir from fluid‐rock interaction, which could lead to wellbore instability or reservoir compaction. To better understand potential relationship between mechanical degradation with various carbonate cement textures and compositions in sandstone reservoirs, six flow‐through experiments were conducted. Formation water (TDS = 5,390 mg/L) enriched with CO2 flowed through two types of Pennsylvanian Morrow B Sandstone: an ankerite‐siderite‐cemented sandstone (disseminated cement texture) and a calcite‐cemented sandstone (poikilotopic cement texture). The experiments produced little change in permeability in the ankerite‐siderite‐cemented sandstone, but permeability increased up to more than 1 order of magnitude in the calcite‐cemented sandstone. Ultrasonic measurements and cylinder‐splitting tests (also known as Brazilian tests) suggested negligible mechanical degradation of the ankerite‐siderite‐cemented sandstone. Variable changes, with significant mechanical degradation in the static moduli, were observed in the calcite‐cemented sandstone. Thus, dissolution of the disseminated ankerite‐siderite cement (0.28–0.30%) had minimal impact on modifying the flow network and the mechanical integrity of the sandstone, whereas dissolution of the poikilotopic calcite cement (0.89–1.13%, quantified with fluid chemistry and visualized with X‐ray microcomputed tomography) impacted the mechanical strength of the sandstone by disconnecting framework grains. With the high water‐to‐rock mass ratios (7.3–8.2) and number of pore volumes (147–675) employed in these experiments, potential risks are most relevant to regions near injection wells. Ultimately, the chemo‐mechanical effects induced by CO2 injection are strongly influenced by the cement texture and composition and the burial history of the reservoir rock. Plain Language Summary: Carbon capture, utilization, and storage is an approach that involves capturing CO2 (carbon dioxide) produced from industrial processes and storing it into sandstone reservoirs (a porous sedimentary rock) to reduce CO2 emissions and mitigate global climate change. This leads to complex subsurface processes, which can change physical, chemical, and mechanical properties in the reservoirs. To quantify these coupled processes, we conducted flow‐through experiments (injecting CO2‐rich fluid into sandstone plugs) on two types of sandstones with different cements. We monitored for flow and chemistry changes, performed 2‐D and 3‐D image analyses, and conducted rock mechanics experiments. The CO2‐induced dissolution of the ankerite‐siderite cement dispersing in the pore space had minimal impact on changing the flow network and the mechanical properties of the sandstone, whereas dissolution of the calcite cement completely filling the pore space impacted the mechanical properties of the sandstone by disconnecting framework grains. With high water‐to‐rock mass ratios and the compacted sandstone samples employed in the experiments, the potential risks are most relevant to regions near injection wells. Ultimately, the CO2‐induced mechanical weakening of sandstone is strongly influenced by the cement texture and composition, as well as the burial history of the reservoir rock. Key Points: CO2‐induced dissolution in disseminated ankerite‐siderite‐cemented sandstone yields little change in permeability and mechanical propertiesCO2‐induced dissolution in poikilotopic calcite‐cemented sandstone yields little to significant permeability and mechanical property changesChemo‐mechanical degradation is highly controlled by the cement texture and composition, as well as the burial history of the rock [ABSTRACT FROM AUTHOR]