Navajo Sandstone–brine–CO2 interaction: implications for geological carbon sequestration

Abstract

The injection of CO 2 into deep saline aquifers is being considered as an option for greenhouse gas mitigation. However, the response of an aquifer to the injected CO 2 is largely unknown. Experiments involving the reaction of Navajo Sandstone with acidic brine were conducted at 200°C and 25 or 30 MPa to evaluate the extent of fluidrock interactions. The first experiment examined sandstone interaction with CO 2 -impregnated brine; the second experiment examined sandstone dissolution in CO 2 -free acidic brine; the third one is carried out in a mixed-flow reactor and designed to measure sandstone dissolution rates based on time-series Si concentrations. The solution chemistry data indicate that the SiO 2 (aq) increases gradually and pH increases slowly with reaction progress. Silicate minerals in the sandstone display textures (dissolution features, secondary mineralization), indicating that these phases are reacting strongly with the fluid. Dissolution of feldspars and conversion of smectite to illite are likely to be the two reactions that contribute to the release of SiO 2 (aq). The product minerals present at the end of the experiments are illite, illite/smectite, allophane, and carbonate minerals (for the CO 2 -charged system). Dissolved CO 2 is likely to acidify the brine and to provide a source of carbon for the precipitation of carbonate minerals. Mineral trapping through the precipitation of carbonate minerals is favored thermodynamically and was observed in the experiments. The chemical reactions likely increase the bulk porosity of the sandstone due to dissolution of silicate minerals. However, allophane and illite/smectite fill voids in sandstone grains. There is no evidence for the removal of clay coatings due to chemical reactions. It is uncertain whether the mechanical forces near an injection well would mobilize the smectite and allophane and clog pore throats. Trace amounts of metals, including Cu, Zn, and Ba, were mobilized.

Geochemical Implications of CO2 Leakage Associated with Geologic Storage: A Review

“…The distribution of CO 2 between the supercritical plume and aqueous phase (CO 2 sequestered via solubility trapping) will depend on aquifer temperature and pressure, as well as formation water composition (Celia and Nordbotten 2009;Bachu 2003;Duan and Sun 2003;Kharaka et al 2006). The reactivity of both phases towards geologic and manmade materials (e.g., cement and steel used in well construction) has been extensively studied under conditions consistent with deep storage formations (Loring et al 2011;McGrail et al 2009;Bearat et al 2006;Shao et al 2010aShao et al , 2010bShao et al , 2011Hu et al 2011;Jacquemet et al 2008;Kutchko et al 2007Kutchko et al , 2008Kutchko et al , 2009Lu et al 2011;Regnault et al 2005;Palandri et al 2005;Soong et al 2004;Kaszuba et al 2003;Sorai et al 2003). Although results from some of these studies are discussed in this report, reactions in deep storage aquifers are not the primary focus of this review.…”

“…The formation of these new mineral phases could serve to reduce the mobility of contaminants in near-surface environments via incorporation into the mineral structure and/or sorption to the mineral surface. For example, the ability of secondary minerals (e.g., allophane (Lu et al 2011), goethite (Hu et al 2011), and highly weathered soils with pH-dependent, positively charged reactive surface groups to adsorb oxyanion contaminants (e.g., nitrate, arsenate, arsenite, chromate, selenate) under acidic conditions is well known (Opiso et al 2009;Arai et al 2005;Giménez et al 2007;Rovira et al 2008). In addition, clays (e.g., illite and smectites [Lu et al 2011] with permanent negatively charged surfaces are also known to adsorb cationic contaminants Poinssot et al 1999).…”

“…For example, the ability of secondary minerals (e.g., allophane (Lu et al 2011), goethite (Hu et al 2011), and highly weathered soils with pH-dependent, positively charged reactive surface groups to adsorb oxyanion contaminants (e.g., nitrate, arsenate, arsenite, chromate, selenate) under acidic conditions is well known (Opiso et al 2009;Arai et al 2005;Giménez et al 2007;Rovira et al 2008). In addition, clays (e.g., illite and smectites [Lu et al 2011] with permanent negatively charged surfaces are also known to adsorb cationic contaminants Poinssot et al 1999). In basaltic systems, the weathering effect of the intruding CO 2 on basalts to form the ferrogenous smectite-like minerals, such as nontronite, could also serve to enhance the immobilization of redox-sensitive contaminants (Vingiani et al 2004;Mason et al 1997;Benson and Teague 1982;Jaisi et al 2009).…”

Injection of coal fly ash slurry in deep saline formations for improved CO2 confinement – A theoretical concept

“…sandstone) in saline formations with injected CO 2 is essential to predict the short-, medium and long-term fate of CO 2 . Whilst significant effort has been made to better comprehend CO 2 mineralization via carbonate precipitation [4], a lesser amount of information is available on rock-brine-CO 2 interactions following CO 2 injection. It is however known that, depending on the nature of the interactions, they may either cause (1) increased porosity and permeability [5] and (1.a) subsequent greater storage capacity of the intended reservoir, or (1.b) unwanted CO 2 migration outside the boundary layers of the reservoir, or (2) decreased porosity and permeability with reduced injectivity due to mineralization [4].…”

“…Whilst significant effort has been made to better comprehend CO 2 mineralization via carbonate precipitation [4], a lesser amount of information is available on rock-brine-CO 2 interactions following CO 2 injection. It is however known that, depending on the nature of the interactions, they may either cause (1) increased porosity and permeability [5] and (1.a) subsequent greater storage capacity of the intended reservoir, or (1.b) unwanted CO 2 migration outside the boundary layers of the reservoir, or (2) decreased porosity and permeability with reduced injectivity due to mineralization [4]. Details on competing geochemical processes were discussed elsewhere [6,7], but it is evident that some of these processes may alter the integrity of deep saline formations and thereby disrupt the safe, long-term storage of CO 2 .…”