CO2 perturbation in aquifers : reaction kinetics and metals behavior

The aim of this thesis was to investigate hydrogeochemical perturbation induced by CO2 in natural aquifers. In a first step, we used chemical data from natural CO2-rich hydrothermal water. We studied variation of fluid chemical composition as a function of CO2 content in order to evaluate reactivity of minerals composing the initial reservoir. Fluid chemical analyses showed decrease in pH, and systematic enrichment in alkalinity and major cations correlated to increase in CO2 content. Chemical reaction was studied by kinetic approach to estimate variation of mineral reactive surface area as function of CO2 perturbation. Results showed that mineral reactive surface area could varied by two to four orders of magnitude as a function of CO2 perturbation. In a second step a field experiment of injection of water saturated with CO2 in aquifer has been carried out. Analysis of groundwater composition before and after injection allowed to study the impact of CO2 perturbation on water-rock interaction processes. A particular focus was made on dissolved metals behavior. Results showed a decrease in pH (from 7.3 to 5.7), involved with enrichment in alkalinity by a factor two, and by approximately one order of magnitude for dissolved metals (Fe, Mn, Zn) and by a factor two for As. Saturation index showed that dissolution of metals oxide such as ferrihydrite was correlated to iron release. These results showed that, in our field experimental conditions, CO2 perturbation induced an enrichment in dissolved elements with more significant effect on dissolved metals. These results highlight the importance of proper physic-chemical characterization of fluid and reservoir rock and in-situ kinetic of reaction in the eventual option of Co2 geological storageCe travail de thèse a porté sur l'étude des perturbations hydrogéochimiques potentiellement induites par le CO2 dans un aquifère salin profond. Dans un premier temps, cet aspect a été étudié à partir de sources hydrothermales naturellement riches en CO2. Une étude de la composition chimique des eaux en fonction de l'augmentation de leur teneur en CO2 a montré une baisse de pH et un enrichissement systématique en cations majeurs et en alcalinité en fonction de la teneur en CO2. Les réactions en jeu ont été étudiées par une approche cinétique afin d'estimer la réactivité des minéraux en fonction de la perturbation en CO2, par le calcul des variations de surfaces réactives. Les résultats obtenus ont montré que la surface réactive des minéraux pouvait varier de 2 à 4 ordres de grandeur en fonction de la perturbation en CO2. Dans un second temps, une expérience d'injection d'eau saturée en CO2 a été effectuée. Une analyse de la variation de la composition chimique des eaux de l'aquifère, avant et après injection, a permis d'étudier l'impact d'une perturbation par le CO2 sur la composition de l'eau. Une attention particulière a été portée sur le comportement des métaux dissous. Les résultats ont montré une baisse du pH (de 7.3 à 5.7), accompagnée d'un enrichissement en alcalinité, cation majeurs et métaux dissous (Fe, Zn, Mn et As). Les calculs d'indice de saturation ont montré qu'une dissolution des oxydes métalliques type ferrihydrite était corrélée à l'enrichissement en métaux dissous. Une approche de cinétique chimique sur la base des résultats expérimentaux a été proposée. Cela a montré que la dissolution des oxydes métalliques obéissait à des cinétiques d'ordre complexe. Ces résultats montrent que l'effet de la perturbation par le Co2 dans les conditions choisies, engendre un enrichissement en éléments dissous, avec un effet plus significatif sur les métaux. Ces phénomènes devront être regardés de près dans l'éventualité du développement de la technologie de stockage géologique du CO2, an aquifère salin profon

Perturbation de CO2 dans les aquifères : cinétique des réactions et comportement des métaux

Ce travail de thèse a porté sur l'étude des perturbations hydrogéochimiques potentiellement induites par le CO2 dans un aquifère salin profond. Dans un premier temps, cet aspect a été étudié à partir de sources hydrothermales naturellement riches en CO2. Une étude de la composition chimique des eaux en fonction de l'augmentation de leur teneur en CO2 a montré une baisse de pH et un enrichissement systématique en cations majeurs et en alcalinité en fonction de la teneur en CO2. Les réactions en jeu ont été étudiées par une approche cinétique afin d'estimer la réactivité des minéraux en fonction de la perturbation en CO2, par le calcul des variations de surfaces réactives. Les résultats obtenus ont montré que la surface réactive des minéraux pouvait varier de 2 à 4 ordres de grandeur en fonction de la perturbation en CO2. Dans un second temps, une expérience d'injection d'eau saturée en CO2 a été effectuée. Une analyse de la variation de la composition chimique des eaux de l'aquifère, avant et après injection, a permis d'étudier l'impact d'une perturbation par le CO2 sur la composition de l'eau. Une attention particulière a été portée sur le comportement des métaux dissous. Les résultats ont montré une baisse du pH (de 7.3 à 5.7), accompagnée d'un enrichissement en alcalinité, cation majeurs et métaux dissous (Fe, Zn, Mn et As). Les calculs d'indice de saturation ont montré qu'une dissolution des oxydes métalliques type ferrihydrite était corrélée à l'enrichissement en métaux dissous. Une approche de cinétique chimique sur la base des résultats expérimentaux a été proposée. Cela a montré que la dissolution des oxydes métalliques obéissait à des cinétiques d'ordre complexe. Ces résultats montrent que l'effet de la perturbation par le Co2 dans les conditions choisies, engendre un enrichissement en éléments dissous, avec un effet plus significatif sur les métaux. Ces phénomènes devront être regardés de près dans l'éventualité du développement de la technologie de stockage géologique du CO2, an aquifère salin profondThe aim of this thesis was to investigate hydrogeochemical perturbation induced by CO2 in natural aquifers. In a first step, we used chemical data from natural CO2-rich hydrothermal water. We studied variation of fluid chemical composition as a function of CO2 content in order to evaluate reactivity of minerals composing the initial reservoir. Fluid chemical analyses showed decrease in pH, and systematic enrichment in alkalinity and major cations correlated to increase in CO2 content. Chemical reaction was studied by kinetic approach to estimate variation of mineral reactive surface area as function of CO2 perturbation. Results showed that mineral reactive surface area could varied by two to four orders of magnitude as a function of CO2 perturbation. In a second step a field experiment of injection of water saturated with CO2 in aquifer has been carried out. Analysis of groundwater composition before and after injection allowed to study the impact of CO2 perturbation on water-rock interaction processes. A particular focus was made on dissolved metals behavior. Results showed a decrease in pH (from 7.3 to 5.7), involved with enrichment in alkalinity by a factor two, and by approximately one order of magnitude for dissolved metals (Fe, Mn, Zn) and by a factor two for As. Saturation index showed that dissolution of metals oxide such as ferrihydrite was correlated to iron release. These results showed that, in our field experimental conditions, CO2 perturbation induced an enrichment in dissolved elements with more significant effect on dissolved metals. These results highlight the importance of proper physic-chemical characterization of fluid and reservoir rock and in-situ kinetic of reaction in the eventual option of Co2 geological storag

Contribution of the reactive mineral surface area on CO2 mineralization under natural conditions

A natural hydrothermal field is considered to be a useful analogue of carbon dioxide mineralization because it integrates the long-term interaction signal. The hydrothermal field of Galicia is characterized fluids resulting from a granit reservoir with pCO2 from 103 to 105 Pa and pH from 10 to 6. Fluids are characterized by an increase of major elements correlated to pCO2. We evaluated the effect of deep CO2 perturbation We evaluated the effects of deep CO2 perturbation on the fluid-rock interaction system. Mineral reactivity which produces changes in the fluid mineral composition is mainly dependent on the 'real' reactive surface area. The mineral surface area participating in reactions resulting from this pCO2 gradient was estimated by an inverse model approach. Input data was based on the chemical composition of the fluids we sampled. The rate of mineral dissolution was estimated by the observed pH and equilibrium conditions. Moreover, the major elemental concentrations allowed us to quantify the variation of the reactive surface area of minerals involved with the overall water-rock interaction. The irreversible mass transfer process, ruled by the continuum equilibrium condition, was defined by the overall degree of reaction advancement, using a set of polynomial equations solved independently of time scale.We found that reactive surface area of calcite, albite and K-feldspar increases by 2 orders of magnitude over the entire CO2 fluid-rock interaction process, while the reactive surface area of biotite increases by 4 orders of magnitude. This shows that fluid neutralisation and consequent CO2 mineralization under the form of carbonate species is greatly dependent on the behaviour of the reactive surface area of the mineral association in this geological context. We propose that biotite plays a basic role on the pH stabilisation and redox control of environmental perturbation and CO2 mineralization

Géochimie du stockage géologique du CO2 outils d’études des risques de remobilisation des métaux lourds

Carbon Capture and Storage (CCS) is considered as potential solution to mitigate accumulation of greenhouse gas into the atmosphere. However, since many years, several works highlighted the potential environmental impact of those technologies for a long term prospective. Special focus is based on the risk of remobilisation and transfer of metals species into groundwater induced by CO2 perturbation. We performed a field experiment based on single well injection of small volume (3m3) of water-CO2 saturated. This experience was performed in aquifer presented a rock reservoir naturally concentrated in different metals species (Fe, Mn, U, As, Zn, Pb, etc.). We found that CO2 perturbation produced important quantity of carbonate, and an enrichment of several orders of magnitude in metal species concentration (Fe, Mn, Zn, As, etc.) into the groundwater. We propose that acidification due to CO2 injection induced dissolution of minerals, as a first source of metals species. Result showed different enrichment factors, depending on measured metals species. Those differences can be explained by secondary reaction of complexation of metals by carbonate species which could have increased the release of metals species into the groundwater.Le stockage géologique du CO2 est l’une des solutions envisagées pour limiter l’accumulation de ce gaz à effet de serre dans l’atmosphère. La technique consiste à capter le CO2 auprès des sources d’émissions concentrées (centrales thermiques, chaufferies, cimenteries, etc.), à le transporter, puis à l’injecter dans des roches réservoirs profondes où il devra rester isolé de la surface pendant plusieurs milliers d’années. Les sites de stockage ciblés sont principalement des « aquifères salins profonds », qui sont des réservoirs d’eau profonde à forte salinité (ou « saumure »), non utilisable pour l’eau potable, ainsi que d’anciens réservoirs d’hydrocarbures épuisés ou encore des couches de charbon, du fait de leur grande capacité d’absorption du CO2. Dans le cas des aquifères salins profonds, option étudiée ici, le stockage de CO2 s’effectue à la fois par un piégeage mécanique au sein du réservoir étanche, mais également par interactions physico-chimiques entre l’eau en place et la roche réservoir. Ces interactions CO2-eau-roche piègent du CO2 par dissolution et par précipitation de nouveaux minéraux. Ces processus sont dépendants de nombreux paramètres intrinsèques du réservoir profond tels que la pression, la température, la porosité, la perméabilité, la composition minéralogique de la roche réservoir, la composition chimique de l’eau, etc.Dans ce contexte, l’INERIS étudie les risques liés à cette technologie émergent

Estimation of reactive surface area of the minerals during fluid-rock interaction in Galicia (Spain) : Analog for artificial geological sequestration of CO2

The understanding of complex reactions between CO2 rich fluids and rocks is basic in prospecting safety for long term CO2 storage in natural geological reservoirs. Hydrothermal natural fields are considered one of the best analogue for carbon dioxide mineralization because integrate the signal of long term interaction. The Spanish hydrothermal field of Galicia is characterized by co-genetic fluids issued from a quite-homogeneous granitic reservoir. Here, fluids are characterized by an increase on major elements (Ca, Mg, K and Na) and alkalinity associated to the 4-fold decrease on fluid pH (pH from 10 to 6). This natural situation has been used to evaluate the effect of CO2 on the long term fluid -rock interaction. In this work is reported the result of an original methodology applied to the estimation of the reactive surface area of the minerals participating to CO2 neutralization. The adopted methodology is based on an inverse model approach using the chemistry of the sampled fluids. The irreversible mass transfer process is defined by the overall degree of reaction advancement assuming that ion activity of dissolved silica and aluminium ions are limited by the equilibrium with quartz and kaolinite. A system of dissolution equation for the main rock mineral is solved in terms of a transposed reaction rate vector, introducing experimental kinetic rate constants and solving for the surface area of dissolving minerals. Preliminary results indicate that dissolution rate of oligoclase, albite, K-feldspath, and biotite remains quite constant. On the contrary the reactive surface area of oligoclase and biotite changes by 1 - 2 order(s) of magnitude and the reactive surface area of albite and K-feldspar changes 2 - 3 orders of magnitude in the estimated 50 000 years of interaction. Those results suggest that mineral surfaces reactive area can varied by several order of magnitude over the water-rock interaction process, while classical geochemical model integrate a constant reactive surface mineral in there simulations. Keywords: Natural analog, CO2-water-rock interaction, kinetic rate dissolution, inverse geochemical modelin

Estimating the reactive surface area of minerals in natural hydrothermal fields : preliminary results

International audienceWe estimated variation of reactive surface area (RSA) of minerals in the Galician (Spain) geothermal field using the chemical composition of fluids as input data. Our methodology is based on reconstructing the fluid composition according to a reaction progress schema that uses the fractional degree of advancement of the mass-transfer process. RSA of the principal mineral is estimated by using a transposed reaction rate that introduces experimental kinetic rate constants. We found that over the entire reaction process, RSA of feldspars and biotite varied by 2-4 orders of magnitude, thereby explaining the changes observed in CO2 partial pressure and fluid pH

Limiting the risk inherent to geological CO2 storage: The importance of predicting inorganic and organic chemical species behavior under supercritical CO2 fluid conditions

International audienceField tests have clearly demonstrated that injecting CO2 in geological storage sites results in the release of heavy metals and organic species to groundwater, implying that CO2 injection may have potentially dramatic consequences for the environment. Numerous laboratory experiments using rock and cement samples from different geological formations typical of injection sites show that rocks reacting with synthetic or natural fluids and supercritical CO2 at their respective temperature and pressure conditions generate fluids with As, Cr, Cu, Cd, Pb, Fe, and Mn concentrations above Environmental Protection Agency drinking water standards. The solubility of a compound in supercritical-CO2 (sc-CO2), expressed in terms of the compound's activity or fugacity, also depends on the composition of the phases present at the pressure and temperature of the storage site. In a brine sc-CO2 system, estimating the activity of an inorganic compound or the fugacity of an organic compound is a prerequisite to predicting the solubility of a compound in sc-CO2 phases. Available models (e.g. Pitzer equations) require the use of binary salt concentrations and are best applicable to polar ionic compounds; but the effect of brines on larger hydrocarbons has not yet been explored. New experimental data will be needed to determine the magnitude of pH effects on the partitioning behavior of organic acids and trace metal complexes from brine to sc-CO2

Geochemical assessment of CO2 perturbation in a shallow aquifer evaluated by a push-pull field experiment

International audienceA field experiment was conducted using a push-pull test method in a shallow aquifer to investigate the potential impact of CO2 leakage on groundwater chemistry. The push-pull test was performed using a volume of groundwater previously pumped from the aquifer that was saturated in CO2 and introduced into a fractured sandstone aquifer before re-pumping it. Groundwater pH, alkalinity, electric conductivity, redox potential and FeII were measured on-site. A specific protocol was established to avoid oxidation during sampling. Field measurements and laboratory analyses showed rapid and systematic changes in pH and alkalinity as well as an increase in the aqueous concentrations of major cations (Ca, Mg) and trace element species (Fe, Mn, Zn, As). Thermodynamic calculations taking into account both redox and pH sensitive reactions indicated that trace elements may be mobilized as the result of the dissolution of metal oxide minerals. A simplified kinetic model, based on quantitative analyses provided by a mixing model, showed that the trace element release rate is ruled by a reaction of complex order with respect to pH, suggesting the influence of metal complexation reactions, involving bicarbonate and sulfate anions. Results suggest that, in the case of potential CO2 leakage in subsurface aquifers, the remobilization of bivalent metal cations (Fe, Mn, Zn) is relatively high, while it is limited for other elements such as As, Ca or Mg. This study provides a new data set for evaluating the impact of CO2 leakage in shallow aquifers and proposes specific methods for analyzing reaction pathways and kinetic reaction rates at the field scale

Kinetic rate of iron release during artificial CO2 injection in a shallow aquifer : preliminary results

International audienceWe performed an injection of CO2-saturated water in a shallow aquifer following a 'push-pull' test protocol. A specific protocol was designed to measure in situ fluid pH and redox potential with careful sampling. We found increases of dissolved calcium, magnesium, alkalinity, iron and manganese, and other trace elements. Concentrations of Fe resulting from reactivity were estimated using measured concentrations of Fe corrected by a calculated fluid dynamics coefficient. Thermodynamic equilibrium calculations suggested that ferrihydrite Fe(OH)3 dissolution is the main source of iron release. The kinetic rate of Fe(OH)3 dissolution estimated by a surface protonation model indicates that the reaction order is two. Since laboratory experimental results show a reaction order of zero, we propose that the mechanism of ferrihydrite dissolution proceeds by a more complex mechanism under natural conditions

Behavior of rare earth elements in an aquifer perturbed by CO2 injection: Environmental implications

International audienceThree cubic-meters of CO2-saturated water was injected into a subsurface fractured aquifer in a post-mined area, using a push-pull test protocol. Groundwater samples were collected before and after CO2-injection to quantify geochemical changes. CO2-injection initially reduced the pH of water from 7.3 to 5.7, led to the enrichment of major ions (Ca2+, Mg2+, and alkalinity), and dissolved trace metals (including Fe, Mn, As, and Zn) in the groundwater. Rare earth elements (REE) and yttrium concentrations were also measured in these samples before and after CO2 perturbation, to evaluate their behavior. An enrichment of total Y plus REE (REY) occurred. REY fractionation was observed with higher heavy REE (HREE) enrichment compared to light REE (LREE), and significant variations in La/Yb and Y/Ho ratios were observed following CO2 perturbation. Enrichment by a factor of three was observed for Y, Lu, and Tm, and by nearly one order of magnitude for Dy and Yb. A geochemical model was used to evaluate the amount of REE aqueous ions complexed throughout the experiment. Modeling of the results showed that speciation of dissolved REE with carbonate, along with desorption from iron oxyhydroxide surface were the main factors controlling REE behavior. This study increases an understanding of dissolved REE behavior in the environment, and the potential use for applying iron oxides for REE recovery from mine drainages. Furthermore, the description of REE fractionation patterns may assist in surveying CO2 geological storage sites, surveying underground waste disposal sites, and for understanding the formation of ore deposits and fluid inclusions in geological formations