Evaluating CO2 breakthrough in a shaly caprock material: a multi-scale experimental approach

Stavropoulou, Eleni; Laloui, Lyesse

doi:10.1038/s41598-022-14793-8

Cited by 11 publications

(3 citation statements)

References 37 publications

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“…A cylindrical cell made out of PEEK is used for the application of the various boundary conditions, that are explained in detail in the following sections. The so called PEEKcell, is designed to host 5 mm × 5 mm cylindrical samples and can sustain a maximal pressure and temperature of 20 MPa and 80 • C respectively (Stavropoulou and Laloui, 2022). An entry on each side of the cell (top and bottom) allows the application of confining pressure (top) and pore pressure on the sample (bottom).…”

Section: In-situ X-ray Micro-tomography and Experimental Protocolmentioning

confidence: 99%

Insights into the interaction of a shale with CO₂

Stavropoulou

Laloui

2022

Preprint

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Abstract. Caprock formations such as shales, play a key role to safe underground CO2 storage since they serve as a hydromechanical barrier that prevents migration of the injected CO2 to the surface. While their hydromechanical response is important to ensure their sealing capacity, interaction with the injected CO2 involves additional thermo-chemo-mechanical (THMC) phenomena that may threaten the long-term caprock’s integrity. The low transport properties of shales make them a suitable caprock material, but at the same time challenging to study due to the very long time scales that are required for the various thermo-hydro-chemo-mechanical processes to manifest. In this work, the multiphysical interaction of the Opalinus Clay shale with CO2 is studied with live x-ray tomography. Long-term exposure to liquid and supercritical CO2 targets the investigation of different occurring THMC processes locally and globally in 3D that are often indistinguishable with conventional lab testing protocols. To improve spatial and temporal resolution while applying realistic pressure and temperature conditions, small size samples are studied. Long-term injection of liquid CO2 resulted to a siginificant fissuring of calcite-rich zones that were for the first time visualised and quantified from the x-ray images, while a re-arrangement of the pre-existing micro-fissures in the clay matrix were observed. The volumetric response during direct exposure of an Opalinus Clay sample to supercritical CO2 revealed an initial swelling at pre-cracked zones and initiation of new micro-fissures at areas of direct contact with the anhydrous CO2 due to pore water evaporation. Advanced 3D image analysis showed an increasing CO2 uptake with time the elevated value of which after pressure release suggests potential CO2 trapping the material.

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Section: In-situ X-ray Micro-tomography and Experimental Protocolmentioning

confidence: 99%

Insights into the interaction of a shale with CO₂

Stavropoulou

Laloui

2022

Preprint

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“…Numerous authors have described the wettability of scCO 2 -brine-rock systems . During CGS, water-wettability over scCO 2 is often preferred because it limits upward vertical migration and increases residual trapping in the reservoir [75][76][77], as well as increasing structural trapping, thus reducing the risk of scCO 2 breakthrough in the confining zone [78,79]. Figure 1 shows a literature compilation of scCO 2 -brine-rock contact angles as a function of pressure for sandstone [66], limestone [66], dolomite [55], fine-grained caprocks [49], and source rock [58], measured at similar temperatures (~50 • C).…”

Section: Introductionmentioning

confidence: 99%

Effect of Geochemical Reactivity on ScCO2–Brine–Rock Capillary Displacement: Implications for Carbon Geostorage

Cruz,

Dang,

Curtis

et al. 2023

Energies

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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.

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“…A necessary condition for not having leakage is that the caprock has an adequate sealing capacity, ensured only if the threshold capillary pressure of caprock p * c is larger than the capillary pressure pc due to the CO2 injection. The threshold capillary pressure is experimentally determined through tests in which the non-wetting fluid is forced to penetrate into water-saturated specimen [2]. This work reports the results of two threshold tests performed on remoulded caprock specimens using CO2 in supercritical conditions (scCO2) and air as non-wetting fluid.…”

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confidence: 99%

CO2 storage: threshold capillary pressure estimate in a remoulded caprock specimen

Vespo,

Stavropoulou,

Volonté

et al. 2023

SEG

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The underground permanent storage of CO2 is one of the actions promoted by the European Union to achieve neutrality in terms of carbon emissions by 2050.It is the only readily available option for so-called hard-to-abate sectors such as cement, steel, chemical plants, where a significant proportion of carbon dioxide emissions are linked to the industrial process and therefore cannot be avoided by means of electrification or renewables [1]. Ideal geological storage should be able to store CO2 for millions of years and maintain 99% of stored CO2 for at least a thousand years. A necessary condition for not having leakage is that the caprock has an adequate sealing capacity, ensured only if the threshold capillary pressure of caprock p*c is larger than the capillary pressure pc due to the CO2 injection. The threshold capillary pressure is experimentally determined through tests in which the non-wetting fluid is forced to penetrate into water-saturated specimen [2]. This work reports the results of two threshold tests performed on remoulded caprock specimens using CO2 in supercritical conditions (scCO2) and air as non-wetting fluid. The tested material is a non-plastic silty clay with liquid limit wL= 50% and plastic limit wP= 25%. It comes from a disturbed core extracted from a deep formation in the Po Valley (Italy). The material was mixed with distilled water at w = 1.2 wL and then consolidated in oedometric conditions up to a vertical effective stress of 1.1 MPa. The porosity at this stress state is equal to 0.43. Direct determination of the threshold capillary pressure in the laboratory is achieved by a step-by-step increase of the non-wetting fluid pressure at the inlet of a water-saturated sample, while the water pressure is kept constant at the outlet. When the difference between the non-wetting fluid pressure and the water one is higher than the threshold capillary pressure, water drainage occurs, and the non-wetting fluid can break through the sample [3]. Depending on the permeability, several days might be required for one measurement of p*c for a tight rock. The magnitude of non-wetting pressure steps plays a key role in this methodology, since small pressure increments result in long test times, while large pressure increments result in lower accuracy of the threshold capillary pressure estimation. To be able to perform the test using scCO2 as a non-wetting fluid, it is necessary to set the CO2 pressure greater than 7.4 MPa and maintain the temperature T of the entire experimental apparatus greater than 31.1 °C. A high-pressure oedometric cell [4] is used to perform the step-by-step tests. This device allows the study of specimens with a diameter of 35 mm and a height of 12.5 mm. Water can be injected at both sides of the sample, two different pumps are used to control pressure up to 16 MPa. A third pump connected to the upstream side is used to inject the non-wetting fluid with a range up to 25 MPa. The axial stress is applied with a hydraulic jack that allows the application of a maximum total vertical stress equal to 100 MPa. The vertical displacements are measured by three LVDTs, which measure the relative displacement of the cell with respect to the piston. Two tests were performed to determine the threshold capillary pressure of the remoulded caprock specimen in relation to the following fluid systems: scCO2/H2O and air/H2O. Each threshold test consisted of the following stages: at the beginning the sample was saturated with water (under constant volume) after which a total axial load was applied. After the consolidation was completed, the intrinsic water permeability was assessed (k = 5.2∙10 -18 m2). Then followed the injection stage of non-wetting fluid. In both tests the effective vertical stress was set equal to 1.1 MPa. The water backpressure and the initial value of non-wetting pressure were set equal to 10 MPa in the scCO2 test and 1 MPa in the air test. The former test was conducted at T = 35 °C, the latter at T = 25 °C. Figure 1(a) and Figure 1(b) show the trend of capillary pressure pc and outgoing volume Vout during the scCO2 and air injection stage, respectively. The capillary pressure range for which there was a net increase in the outgoing volume was 500 ÷ 600 kPa in the scCO2 test and 570 ÷ 670 kPa in the air one. The magnitude of outgoing volume implies the overcoming of the threshold capillary pressure p*c and the establishment of a convective flow of non-wetting fluid through the sample. In both tests, no deformation of the specimens occurred during the injection stage. Therefore the difference between the threshold capillary pressure values determined for the two tests, carried out at an effective vertical stress of 1.1 MPa, is about 70 kPa. Instead, using the tangent method to indirectly estimate the threshold capillary pressure, through the pore size distribution of the remoulded caprock (Figure 1 (c)) and the Washburn-Laplace equation, the difference for the two fluid systems would be equal to about 170 kPa (≈ 2.5 times the real experimental value). This would suggest that the tangent method can only be used for a rough estimate and the threshold capillary pressure is not only a function of the pore size distribution, but also largely depends on the actual pore interconnectivity. For a deeper analysis, further experimental tests are in progress.

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Evaluating CO2 breakthrough in a shaly caprock material: a multi-scale experimental approach

Cited by 11 publications

References 37 publications

Insights into the interaction of a shale with CO₂

Insights into the interaction of a shale with CO₂

Effect of Geochemical Reactivity on ScCO2–Brine–Rock Capillary Displacement: Implications for Carbon Geostorage

CO2 storage: threshold capillary pressure estimate in a remoulded caprock specimen

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Evaluating CO2 breakthrough in a shaly caprock material: a multi-scale experimental approach

Cited by 11 publications

References 37 publications

Insights into the interaction of a shale with CO2

Insights into the interaction of a shale with CO2

Effect of Geochemical Reactivity on ScCO2–Brine–Rock Capillary Displacement: Implications for Carbon Geostorage

CO2 storage: threshold capillary pressure estimate in a remoulded caprock specimen

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Insights into the interaction of a shale with CO₂

Insights into the interaction of a shale with CO₂