Link Between CO₂‐Induced Wettability and Pore Architecture Alteration

Abstract

Changes in pore (throat) size, surface roughness, and mineralogy induced by supercritical CO 2-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 CO 2 contact angle changes emerge after Madison Limestone samples were soaked for 400 hr in CO 2-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 CO 2 injectivity, migration, and storage capacity. This fundamental insight into CO 2 geological storage processes should aid practitioners to reduce uncertainties in forecasting CO 2 distribution via injection simulation. Plain Language Summary Emitting a large amount of greenhouse gases into the atmosphere has disrupted the global carbon cycle. CO 2 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 CO 2. 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 CO 2 surface wetting and thereby capillary pressure and relative permeability.

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

“…Geochemical reactions arising from the dissolution of scCO 2 in brine have been experimentally proven to impact the microstructure of storage zones [89][90][91] and confining zones [60,69,73,[92][93][94][95][96][97][98] even at short treatment times of typically few weeks. The impact on storage zones is commonly observed by dynamic injection flooding of scCO 2 -enriched brine in limestone core samples.…”

“…Dynamic scCO 2enriched brine injection tests on limestone cores show strong calcite dissolution and enlargement of pore throats in the inlet of the core, followed by slight mineral precipitation in the far region [89,90]. Additionally, an increase in the limestone scCO 2 -wettability was observed after scCO 2 -enriched brine treatment [90,91].…”

“…Recent studies have evaluated the role of geochemical alterations induced by scCO2brine interactions in the capillary properties of the storage zone [89][90][91] and confining zone [60,69,73,[92][93][94][95][96][97][98]. Due to their high reactivity, limestones are generally the storage rock of focus, given that the reactivity of sandstones (mainly quartz) is extremely slow and pH-independent [16,83].…”

“…A secondary alteration of feldspars can occur when the concentration of calcium ions deriving from the dissolution of carbonates plus originally occurring in the brine is considerable [80,88]. An example is the dissolution of albite consuming Ca 2+ and leading to the precipitation of calcite and kaolinite [80]: Recent studies have evaluated the role of geochemical alterations induced by scCO 2 -brine interactions in the capillary properties of the storage zone [89][90][91] and confining zone [60,69,73,[92][93][94][95][96][97][98]. Due to their high reactivity, limestones are generally the storage rock of focus, given that the reactivity of sandstones (mainly quartz) is extremely slow and pH-independent [16,83].…”

“…Due to their high reactivity, limestones are generally the storage rock of focus, given that the reactivity of sandstones (mainly quartz) is extremely slow and pH-independent [16,83]. Dynamic scCO 2enriched brine injection tests on limestone cores show strong calcite dissolution and enlargement of pore throats in the inlet of the core, followed by slight mineral precipitation in the far region [89,90]. Additionally, an increase in the limestone scCO 2 -wettability was observed after scCO 2 -enriched brine treatment [90,91].…”