Abstract
Abstract. Geological carbon sequestration provides permanent CO2 storage to mitigate the current high concentration of CO2 in the atmosphere. CO2 mineralization in basalts has been proven to be one of the most secure storage options. For successful implementation and future improvements of this technology, the time-dependent deformation behavior of reservoir rocks in the presence of reactive fluids needs to be studied in detail. We conducted load-stepping creep experiments on basalts from the CarbFix site (Iceland) under several pore fluid conditions (dry, H2O saturated and H2O + CO2 saturated) at temperature, T≈80 ∘C and effective pressure, Peff=50 MPa, during which we collected mechanical, acoustic and pore fluid chemistry data. We observed transient creep at stresses as low as 11 % of the failure strength. Acoustic emissions (AEs) correlated strongly with strain accumulation, indicating that the creep deformation was a brittle process in agreement with microstructural observations. The rate and magnitude of AEs were higher in fluid-saturated experiments than in dry conditions. We infer that the predominant mechanism governing creep deformation is time- and stress-dependent subcritical dilatant cracking. Our results suggest that the presence of aqueous fluids exerts first-order control on creep deformation of basaltic rocks, while the composition of the fluids plays only a secondary role under the studied conditions.
Highlights
The concentration of atmospheric CO2 has seen a significant increase over the last century, raising concerns about the more frequent occurrence of extreme weather, sea-level rise and the projected increase of average global temperature (Broecker, 1975)
It is estimated that about 800 Gt CO2 will need to be stored by the end of the century to keep the global temperature increase below 1.5 ◦C compared to preindustrial levels (National Academies of Sciences, Engineering, 2019)
In experiments where pore fluids were present (H2O and H2O + CO2), the strain accumulated during the phase I creep systematically increased with increasing stress, and the creep strain rate during the phase II
Summary
The concentration of atmospheric CO2 has seen a significant increase over the last century, raising concerns about the more frequent occurrence of extreme weather, sea-level rise and the projected increase of average global temperature (Broecker, 1975). It is estimated that about 800 Gt CO2 will need to be stored by the end of the century to keep the global temperature increase below 1.5 ◦C compared to preindustrial levels (National Academies of Sciences, Engineering, 2019). Such large volumes can practically be stored in the subsurface. Geological carbon sequestration (GCS) by in situ carbon mineralization is recognized as one of the most secure, long-term storage solutions (Gislason and Oelkers, 2014; Kelemen and Matter, 2008; Lackner et al, 1995; Mani et al, 2008; Seifritz, 1990; Snæbjörnsdóttir et al, 2020; Tutolo et al, 2021). Relevant fluid and mineral reactions can be formulated as follows (Hangx and Spiers, 2009; Hansen et al, 2005; Kelemen and Matter, 2008; Oelkers et al, 2008): Dissociation: CO2 + H2O H2CO3
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