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Changes in pore (throat) size, surface roughness, and mineralogy induced by supercritical CO2‐water‐rock reactions impact petrophysical properties such as porosity, permeability, and especially wettability. Herein, we show that these changes directly impact relative permeability and capillary pressure curves, a fact rarely studied in the literature. In this work, we show that CO2 contact angle changes emerge after Madison Limestone samples were soaked for 400 hr in CO2‐enriched brine. Coreflooding results show that the water production rate and cumulative water production increased after the rock was exposed to carbonic acid. Moreover, the mercury capillary pressure decreased in mesopores and macropores, indicating the increase of size in these pores due to reactions. This compounded wettability and pore network alteration can directly affect CO2 injectivity, migration, and storage capacity. This fundamental insight into CO2 geological storage processes should aid practitioners to reduce uncertainties in forecasting CO2 distribution via injection simulation. Plain Language Summary: Emitting a large amount of greenhouse gases into the atmosphere has disrupted the global carbon cycle. CO2 captured from various sources could be transported to a close‐by site for injection into deep saline aquifers or oil/gas reservoirs for storage or/and enhanced oil recovery. Reactions between the rock and the carbonic acid can alter the rock fabric. These reactions can change rock properties, for example, pore structure, porosity, permeability, and wettability. These changes can affect capillary pressure and relative permeability. These rock alterations can significantly impact the fate of the injected CO2. Despite efforts made to determine changes in pore architecture or petrophysical properties, a few studies have investigated the impact of rock alteration on multiphase flow properties, namely, capillary pressure and relative permeability. Even less is understood on this subject when diffusion dominates over convective transport. Here we focused on changes in pore (throat) size distribution and wettability, and dynamic properties, as induced by geochemical reactions. We observed pore enlargement among the larger pores (mesopores to macropores) due to mineral dissolution, which contrasts with a decreased size in smaller pores (micropores), resulting from mineral precipitation. These processes lead to a more CO2 surface wetting and thereby capillary pressure and relative permeability. Key Points: CO2‐brine‐rock reactions at reservoir conditions improve CO2 wettabilityGeochemical reactions alter the rock pore architecture and multiphase flow responseMultiphase flow alterations correlate well with changes in wettability and pore structure [ABSTRACT FROM AUTHOR]

Abstract: The potential impact to the integrity of wellbore cements as a result of exposure to supercritical carbon dioxide (SCCO2) has been raised as an area of some concern with respect to long-term effectiveness of CO2 storage in geological formations. In flow-through experiments we simulated diffusion of brine and SCCO2 from the interface between wellbore cement and caprock into a fracture-bearing Portland cement. The experiments were performed at in-situ reservoir pressure (pore pressure: 19.9 MPa) and temperature (54 °C) conditions for 113 days. For this purpose we saturated illite-rich shale and the Portland cement core (2.02 cm×5.35 cm) with 1.65 M brine for 14 days. After this period of time we injected SCCO2 into the system for 99 days and simulated a diffusion process by using a pressure gradient of 0.7 MPa. Calcite precipitation occurred within the fracture and the induced pressure of crystal growth may explain an increase in the relative permeability along the fracture with time. SCCO2-induced reactions extended ~5 mm into the Portland cement core from the fracture and formed an orange-colored zone. The orange-colored zone is nearly completely carbonated with crystalline phases consisting mainly of calcite, aragonite, and vaterite. The only crystalline cement component that persisted in the orange-colored zone was brownmillerite. Interior portions of the hydrated cement were partially carbonated, modified in texture and contained newly formed calcite, hydrogarnet and hydrocalumite (Friedel''s salt). Cement porosity decreased from 37.8% to 23.8% during carbonation and was associated with a 19.6% increase in mass. [Copyright &y& Elsevier]

[Display omitted] • Rock-carbonic acid reactions without flow differ qualitatively from those with flow. • Time-domain NMR served as a powerful characterization tool for rock alteration. • Rock type is this dolostone strongly affected the outcome of geochemical reactions. Geologic carbon sequestration (GCS) is considered a feasible technology for storing substantive volumes of greenhouse gases in subsurface geological formations. In the reservoir, far from carbon dioxide (CO 2) injection wells or in post-injection scenarios, diffusion dominates over advection. This condition conjoins with spatially distributed geochemical reactions to induce heterogeneous changes in pore architecture, i.e. pore body and throat sizes or surface roughness. These changes can affect CO 2 transport properties and storage capacity. In this work, we investigated mineral dissolution and precipitation in dolomite samples saturated with a CO 2 -saturated brine at 93 ° C and 34.5 MPa, aged without flow. Two rock types samples, i.e. intergranular- and vuggy-dominant, were selected to investigate changes in pore size, porosity and permeability under reactive conditions. Mineral dissolution and precipitation were characterized using scanning electron microscopy. Changes in pore size were quantified via time-domain nuclear magnetic resonance (TD-NMR) transverse relaxation time (T 2) and diffusion coefficient (D) distributions. We show that mineral dissolution likely occurs in highly permeable pathways. These observations are confirmed through analysis of (T 2) and diffusion coefficient (D) distributions. In contrast to results during CO 2 -enriched brine continuous injection, mineral precipitation was observed in micropores. The leftward shift of the T 2 peaks, corresponding to micropores, also evidenced mineral precipitation in low-permeability zones. However, microscale alterations resulted only in a subtle increase in porosity and permeability. Results in this study shed light on effects of geochemical reactions on alteration of rock properties in diffusion-dominated regions during CO 2 storage. [ABSTRACT FROM AUTHOR]