Abstract
AbstractThe presence of calcium‐cemented ash beds serving as caprocks in hydrothermal systems calls for the examination of any chemo‐mechanical processes that may undermine or enhance their sealing capacity. Understanding these processes provides new information regarding how to model time‐dependent observations associated with seismicity and/or deformation in volcanic areas. In addition, since these ash beds are inherently similar to ash‐based concrete, a bridge of knowledge can be built across disciplines in the earth sciences and engineering. This paper investigates how the permeability of a volcanic ash cemented with hydrated lime changes upon exposure to carbon dioxide (CO2) in humid and hydrous conditions relevant to natural or human‐driven processes such as those found in hydrothermal settings or near wellbores used for secondary oil recovery, CO2 plume geothermal energy, or carbon storage. We characterized samples by their permeability during carbonation and subsequent changes in pore pressure and confining pressure. Products from the reaction of CO2 with the cemented ash matrix reduced permeability and entrapped fluids. The regions within samples permeated with unreacted CO2 were susceptible to fracturing upon rapid depressurization, but only when the effective stress state was sufficiently low. Altogether, the results indicate that lime‐cemented volcanic ash beds are particularly suited to act as flow barriers to CO2‐rich fluids.
Highlights
Mineral carbonation occurs when CO2 gas dissolves into the adsorbed or capillary water of a solid containing metal oxides or silicates and triggers a chemical reaction that produces carbonate salts
This paper investigates how the permeability of a volcanic ash cemented with hydrated lime changes upon exposure to carbon dioxide (CO2) in humid and hydrous conditions relevant to natural or humandriven processes such as those found in hydrothermal settings or near wellbores used for secondary oil recovery, CO2 plume geothermal energy, or carbon storage
The inclusion of lightweight aggregates in CVA5c resulted in a lower grain density than CVA1, whereas porosity and permeability values were most heavily influenced by packing pressure during casting and ended up similar to those measured for Portland cements cured under wellbore downhole conditions (Fabbri et al, 2009; Rimmelé et al, 2008)
Summary
Mineral carbonation occurs when CO2 gas dissolves into the adsorbed or capillary (or in select cases, bound) water of a solid containing metal oxides or silicates (or hydrates of these) and triggers a chemical reaction that produces carbonate salts. The two constituents of modern cement mixes that are usually inspected are calcium hydroxide (i.e., portlandite, slaked lime, or hydrated lime) and C-S-H. Their respective carbonation reactions can be represented by the following equations: Ca(OH)2 + CO2(aq) → CaCO3 + H2O (1.1). Where the precise stoichiometry of the second reaction is not necessarily known due to the complexities of C-S-H decalcification and silica gel hydration (Morandeau et al, 2014). In both cases the precipitation of calcium carbonate (CaCO3) into the pore space changes local porosity, permeability, elasticity, and strength. As a result some have proposed to leverage carbonation in order to enhance wellbore cement (Lee et al, 2016), repair seal-compromised reservoirs (Ito et al, 2014), and otherwise control permeability in the subsurface (Tao et al, 2016)
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