Search Results (4)

The displacement efficiency of supercritical CO₂ (scCO₂) injection in the storage zone and its primary trapping mechanism in the confining zone are strongly tied to the capillary phenomenon. Previous studies have indicated that the capillary phenomenon can be affected by geochemical reactivity induced by scCO₂ dissolution in formation brine. To quantify such changes, thin disk samples representing a sandstone storage reservoir, siltstone confining zone, and mudstone confining zone were treated under a scCO₂-enriched brine static condition for 21 days at 65 °C and 20.7 MPa. Geochemical alterations were assessed at the surface level using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray fluorescence. Before and after treatment, the wettability of the scCO₂–brine–rock systems was determined using the captive-bubble method at fluid-equilibrated conditions. Pore size distributions of the bulk rocks were obtained with mercury injection capillary pressure, nuclear magnetic resonance, and isothermal nitrogen adsorption. The results indicate the dissolution of calcite at the surface, while other potentially reactive minerals (e.g., clays, feldspars, and dolomite) remain preserved. Despite alteration of the surface mineralogy, the measured contact angles in the scCO₂–brine–rocks systems do not change significantly. Contact angle values of 42 ± 2° for sandstone and 36 ± 2° for clay-rich siltstone/calcite-rich mudstone were determined before and after treatment. The rocks studied here maintained their water-wettability at elevated conditions and after geochemical reactivity. It is also observed that surface alteration by geochemical effects did not impact the pore size distributions or porosities of the thin disk samples after treatment. These results provide insights into understanding the impact of short-term geochemical reactions on the scCO₂–brine capillary displacement in the storage zone and the risks associated with scCO₂ breakthrough in confining zones. Full article

The long-term safe storage of CO₂ in geological reservoirs requires the understanding of the impact of CO₂ on clay-rich sealing cap rocks. The reactivity of the mixed layer of illite-smectite was investigated to determine the reaction pathways under conditions of supercritical CO₂ (scCO₂) conditions in the context of geological CO₂ storage. A common clay (blue marl from the Guadalquivir Tertiary basin, southern Spain) was tested under brine scCO₂ conditions (100 bar and 35 °C) for 120 and 240 h. The clay sample (blue marl) contains calcite, quartz, illite, smectite, and the corresponding mixed-layer and kaolinite. X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), and inductively coupled plasma optical emission spectroscopy (ICP-OES) analyses were performed. The illitization of mixed-layer illite-smectite was observed by XRD and confirmed by a variation in the content of different elements (K, Mg, Na, Ca, and Fe) of the transformation, as well as an increase in the specific surface (SSA) of the clay (36.1 to 38.1 m²/g by N₂, 14.5 to 15.4 m²/g by CO₂ adsorption). Furthermore, these reactions lead to mineral dissolution and secondary mineral formation along the CO₂–water–clay intercalations of the source rock were responsible for a change in porosity (7.8 to 7.0 nm pore size). The implications of illitisation, mineral destruction, and precipitation processes on CO₂ storage and clay layer integrity should be explored before deciding on a geological storage location. Full article

The effect of supercritical CO₂ on the shaly caprocks is one of the critical issues to be considered in CO₂ sequestration programs. Shale-scCO₂ interactions can alter the seal integrity, leading to environmental problems and bringing into question the effectiveness of the program altogether. Several analytical studies were conducted on samples from Jurassic Eneabba Basal Shale and claystone rich facies of the Triassic Yalgorup Member (725–1417 m) in the Harvey CO₂ sequestration site, Western Australia, to address the shale-scCO₂ interactions and their effect on the petrophysical properties of the caprock. Shale samples saturated with NaCl brine were exposed to scCO₂ under the reservoir condition (T = 60 °C, P = 2000 psi) for nine months and then tested to determine their altered mineralogical, petrophysical and geochemical properties. The experimental study examined changes to the mineralogical composition, capillary threshold pressure, and pore size distribution (PSD) of samples. The X-ray diffraction (XRD) results showed several changes in mineralogy because of rock-brine-CO₂ reactions. Quartz, feldspars, kaolinite, and goethite were dissolved in most samples and muscovite, and halite were precipitated in general. Nuclear magnetic resonance (NMR), low-pressure nitrogen adsorption (LPNA), and mercury injection capillary pressure (MICP) tests indicate an increase in pore volume, except for relatively tighter, clay-rich samples. A reduction in capillary threshold pressures of samples after exposure to scCO₂ is observed. Full article

This study aims at the qualitative and quantitative determination of porosity, mineralogical and textural changes in carbonate rock samples after injection of (i) supercritical CO₂-rich brine and (ii) dry supercritical CO₂, under similar experimental conditions (P ≈ 75 bar, T ≈ 35 °C, 970 h exposure time and no CO₂ flow). The studied rocks were sampled in the western Basque-Cantabrian Basin, North Spain, and consist of vuggy carbonates (“Carniolas”) of the Puerto de la Palombera formation (Hettangian). Mineralogical and pore space characterization is completed using optical microscopy, scanning electron microscopy and optical image analysis. In addition, X-ray fluorescence analyses are performed to refine the mineralogical information and to obtain whole rock geochemical data and the brine composition is analysed before and after the experiment. Mineralogical and chemical results indicate that the carbonate rocks exposed to supercritical CO₂ in dry conditions do not suffer significant changes. However, the injection of supercritical CO₂-rich brine induces chemical and physical changes in the rock due to the high reactivity of calcite at the low pH conditions produced by the acidified brine. Numerical modelling validates the experimental observations. These results can be used to characterize the behaviour of carbonate rocks under conditions similar to the vicinity of a CO₂ injection well. The results should be considered only at the scale of the studied samples and not at reservoir scale. Full article