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.

Owing to the heterogeneity of methane hydrate reservoirs in the South China Sea, hydrate and silty clay particles mostly exist in the form of interbedded reservoirs. Permeability is a decisive factor for the efficiency of interbedded methane hydrate deposits. Therefore, using montmorillonite as the simulated sediment material, permeability measurements of interbedded sediments with different methane hydrate distributions and effective stresses were carried out for the first time in this study. By comparing with homogeneous sediments, the permeability evolution of interbedded sediments under different hydrate distributions and effective stresses is explored, and the effect of methane hydrate dissociation on the permeability of interbedded sediments is analyzed. The results show that the permeability of interbedded sediments with different hydrate saturation levels has little difference and is almost the same as that of pure soil sediments. With the increase of effective stress, the porosity of methane hydrate interbedded sediments decreases and permeability damage is caused, but the final permeability damage is less obvious than that of homogeneous hydrate sediments. In addition, the gas slip effect exists in methane hydrate interbedded sediments. Moreover, the dissociation of methane hydrate causes clay swelling, which leads to the decrease of interbedded permeability, but the degree of permeability damage is lower than that of homogeneous sediments. The results of this study provide a theoretical basis for the development and utilization of interbedded methane hydrate sediments in the South China Sea.

Mineral reactive surface area (RSA) is one of the key factors that control mineral reactions, as it describes how much mineral is accessible and can participate in reactions. This work aims to evaluate the impact of mineral RSA on numerical simulations for CO2 storage at depleted oil fields. The Farnsworth Unit (FWU) in northern Texas was chosen as a case study. A simplified model was used to screen representative cases from 87 RSA combinations to reduce the computational cost. Three selected cases with low, mid, and high RSA values were used for the FWU model. Results suggest that the impact of RSA values on CO2 mineral trapping is more complex than it is on individual reactions. While the low RSA case predicted negligible porosity change and an insignificant amount of CO2 mineral trapping for the FWU model, the mid and high RSA cases forecasted up to 1.19% and 5.04% of porosity reduction due to mineral reactions, and 2.46% and 9.44% of total CO2 trapped in minerals by the end of the 600-year simulation, respectively. The presence of hydrocarbons affects geochemical reactions and can lead to net CO2 mineral trapping, whereas mineral dissolution is forecasted when hydrocarbons are removed from the system.

CO 2 injectivity and storage capacity in sandstone may be impacted by fluid-rock interaction and resultant compaction during carbon sequestration. Although chemical, mineralogical and petrophysical changes are well characterized during fluid-rock interaction in CO 2 -rich systems, the coupling of CO 2 -driven alteration of sandstone with mechanical property changes is less known. Six flow-through experiments were conducted on Pennsylvanian Morrow B Sandstone cores from the Farnsworth Unit in West Texas, USA. CO 2 -rich brine flowed through core samples of poikilotopic calcite-and disseminated ankerite-siderite-cemented sandstone at flow rates that ranged from 0.01 to 0.1 ml/min at 71°C and 29.0 MPa pore fluid pressure. Fluid sample analysis performed by ICP-OES from experiments on both carbonate-cemented sandstones indicate that carbonate cement dissolution is likely the dominant chemical process. The permeability of the ankerite-siderite-cemented sandstone changed little from the reaction with carbonic acid, whereas the permeability of the calcite-cemented sandstone significantly increased by more than one order of magnitude (from 3.3×10 -18 to 7.8×10 -17 m 2 ). P-and S-wave velocities measured from pre-and post-experiment ultrasonic tests were used to estimate the changes in dynamic Young's and shear moduli. Furthermore, cylinder-splitting tests were conducted to measure the tensile strength of the altered post-experimental samples and compared to the control samples that only interacted with pure brine. All samples underwent slight decreases in Young's and shear moduli, and the cylinder-splitting tests suggest that mechanical degradation may be concentrated on the upstream end of the calcite-cemented sample. Our findings help in predicting chemo-mechanical changes at carbon sequestration sites where the reservoir lithology is carbonate-cemented sandstone.