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Interaction of super-critical CO2 with mudrocks: Impact on composition and mechanical properties.

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Title: Interaction of super-critical CO2 with mudrocks: Impact on composition and mechanical properties.
Authors: Dewhurst, David N.1 (AUTHOR) david.dewhurst@csiro.au, Raven, Mark D.2 (AUTHOR), Shah, Sahriza Salwani Bt Md3 (AUTHOR), Ali, Siti Syareena Bt Md3 (AUTHOR), Giwelli, Ausama1 (AUTHOR), Firns, Stephen1 (AUTHOR), Josh, Matthew1 (AUTHOR), White, Cameron1 (AUTHOR)
Source: International Journal of Greenhouse Gas Control. Nov2020, Vol. 102, pN.PAG-N.PAG. 1p.
Subject Terms: *Geological carbon sequestration, *Carbon dioxide, *Geochemistry, Impact (Mechanics), Strains & stresses (Mechanics), Analytical geochemistry, Supercritical carbon dioxide
Abstract: • Geomechanical, mineralogical and geochemical analysis of mudrocks exposed to sCO 2 at high temperature and pressure. • No changes in mineralogy or major element geochemistry noted. • Mudrocks noted to both strengthen and stiffen after exposure to sCO 2 for six months. • Loss of water results in a complete change in geomechanical behaviour from ductile to brittle. Geological storage of carbon dioxide (CO 2) is a long-discussed strategy for avoiding CO 2 discharge into the atmosphere and a few industrial scale projects are underway in this regard. In order to successfully perform such a strategy, it is important that site evaluation takes into account both reservoir and caprock properties in order to trap the CO 2. Many caprocks for such sites are clay-rich mudrocks, hence evaluating their seal capacity and seal integrity are critical for storage sites. Analytical studies on the impact of potential CO 2 -water-rock interaction are an important part of site evaluation since potential geochemical reactions may degrade the seal quality and effectiveness. This paper investigates the impact of static exposure of mudrock seals to super-critical CO 2 (sCO 2) at high temperature and pressure (150˚C, 29 MPa) on the mineralogy (illite-smectite, kaolinite, illite and quartz), major element geochemistry and geomechanical properties of mudrock seals over a six-month period. Mineralogy and geochemistry were determined stepwise from their preserved initial state and after 1, 4 and 6 months exposure to sCO 2 in a batch reactor, with no detectable changes in any of the minerals or elements observed. This is likely due to low reactivity in silicate systems and low volume of pore fluid available to facilitate chemical reactions. Samples for geomechanical testing were exposed to sCO 2 for 6 months only. Geomechanical properties changed significantly between preserved and sCO 2 exposed samples tested under equivalent effective stress conditions, with sCO 2 exposed samples being much stronger and stiffer than their preserved counterparts. Given that no mineralogical and geochemical changes were noted during exposure to sCO 2 , it is most likely that the loss of pore water during sCO 2 exposure resulted in the strengthening and stiffening of these mudrocks. [ABSTRACT FROM AUTHOR]
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Abstract:• Geomechanical, mineralogical and geochemical analysis of mudrocks exposed to sCO 2 at high temperature and pressure. • No changes in mineralogy or major element geochemistry noted. • Mudrocks noted to both strengthen and stiffen after exposure to sCO 2 for six months. • Loss of water results in a complete change in geomechanical behaviour from ductile to brittle. Geological storage of carbon dioxide (CO 2) is a long-discussed strategy for avoiding CO 2 discharge into the atmosphere and a few industrial scale projects are underway in this regard. In order to successfully perform such a strategy, it is important that site evaluation takes into account both reservoir and caprock properties in order to trap the CO 2. Many caprocks for such sites are clay-rich mudrocks, hence evaluating their seal capacity and seal integrity are critical for storage sites. Analytical studies on the impact of potential CO 2 -water-rock interaction are an important part of site evaluation since potential geochemical reactions may degrade the seal quality and effectiveness. This paper investigates the impact of static exposure of mudrock seals to super-critical CO 2 (sCO 2) at high temperature and pressure (150˚C, 29 MPa) on the mineralogy (illite-smectite, kaolinite, illite and quartz), major element geochemistry and geomechanical properties of mudrock seals over a six-month period. Mineralogy and geochemistry were determined stepwise from their preserved initial state and after 1, 4 and 6 months exposure to sCO 2 in a batch reactor, with no detectable changes in any of the minerals or elements observed. This is likely due to low reactivity in silicate systems and low volume of pore fluid available to facilitate chemical reactions. Samples for geomechanical testing were exposed to sCO 2 for 6 months only. Geomechanical properties changed significantly between preserved and sCO 2 exposed samples tested under equivalent effective stress conditions, with sCO 2 exposed samples being much stronger and stiffer than their preserved counterparts. Given that no mineralogical and geochemical changes were noted during exposure to sCO 2 , it is most likely that the loss of pore water during sCO 2 exposure resulted in the strengthening and stiffening of these mudrocks. [ABSTRACT FROM AUTHOR]
ISSN:17505836
DOI:10.1016/j.ijggc.2020.103163