Interaction eau-roche-CO2 en contexte de fuite contrôlée de CO2: apport du monitoring géochimique et isotopique lors d'un cas réel d'injection de CO2

Cette étude montre, dans un cas réel d'injection de CO2, comment une approche multi- isotopique (B, Li, S, O, Sr) combinée aux données chimiques permet (i) de tracer indirectement la réactivité et présence du CO2, (ii) de contraindre et comprendre précisément les interactions eau-roche-CO2 et les réponses isotopiques. L'originalité de ce travail consiste à utiliser des outils isotopiques développés dans les géosciences pour les appliquer à ce contexte particulier. L'idée majeure est d'utiliser ces outils comme traceurs des interactions eau-roche-CO2 afin de détecter toute anomalie de fuites de CO2 non décelables par les autres moyens de monitoring existant

Assessing the potential impacts of CO2 leakage on fresh groundwater: from experiments to predictive models

International audienceGeological storage of CO2 in deep saline aquifers is one of the options considered for the mitigation of CO2 emissions into the atmosphere. A deep geological CO2 storage is not expected to leak, however, potential impacts of CO2 leakage into aquifers overlying deep storage site have to be addressed. . A better understanding on how it could affect groundwater quality, aquifer minerals and trace elements mobilization is necessary to fully characterize a future storage site. Moreover, this characterization is required to evaluate monitoring and remediation plans. As part of the collaborative project CIPRES co-funded by the ANR, we present reactive transport works dedicated to the impact assessment of CCS on fresh groundwaters.In a 3D model using ToughReact v.3, we perform different CO2 leakage scenarios in a confined aquifer. This study focuses on theAlbian aquifer that is a strategic water resource in the Paris Basin. The model is based on groundwater and rock chemistry of the Albian green sand layer (i.e. Quartz, Glauconite, Kaolinite) at 700 m deep. The geochemical model was elaborated from experimental data (Barsotti et al. 2016 and Humez et al. 2014) taking into account kinetics for mineral dissolution, ion exchange and surface complexation processes. The numerical mesh consists of 200 m× 500 m × 60 m. A grid refinement near the leakage point is considered to focus on local phenomena e.g. secondary precipitation, surface processes. The total mesh comprises 21600 cells. The results highlight the importance of sorption processes on trace element mobilization and transport (As, Zn and Ni) in fresh groundwater. Moreover, we distinguish different geochemical behavior (CO2 plume shape, secondary precipitation, desorption...) occurring at different depth and length scale according to the horizontal flow rates and density effects that are influenced by hydrodynamic properties (regional gradient). Coupling geochemical processes and regional flows influence on water chemistry evolution allows to strengthen monitoring and verification plan as well remediation perspectives

CO2 leakage up from a geological storage site to shallow fresh groundwater: CO2-water-rock interaction assessment and development of sensitive monitoring

International audienceThe assessment of environmental impacts of carbon dioxide storage in geological repository requires the investigation of the potential CO2 leakage back into fresh groundwater, particularly with respect to protected groundwater reserves. We are starting a new project whith the aims of developing sensitive monitoring techniques in order to detect potential CO2 leaks and their magnitude as well as their geochemical impacts on the groundwater. In a predictive approach goal, a modelling study of the geochemical impact on fresh groundwaters of a CO2 intrusion during geological storage was performed and serves as a basis for the development of sensitive monitoring techniques (e.g. isotope tracing). Then, isotopic monitoring opportunities will be explored. A modeling study of the geochemical impact on fresh groundwaters of the ingress of CO2 during geological storage was conducted. The 3D model includes (i) storage saline aquifer, (ii) impacted overlying aquifer containing freshwater and (iii) a leakage path way up through an abandoned well represented as 1D porous medium and corresponding to the cement-rock formation interface. This model was used to simulate the supercritical CO2 migration path and the interaction between the fluid and the host rock

A reactive transport model for geochemical mitigation of CO2 leaking into a confined aquifer

Long-term storage of anthropogenic CO2 in the subsurface generally assumes that caprock formations will serve as physical barriers to upward migration of CO2. However, as a precaution and to provide assurances to regulators and the public, monitoring is used detect any unexpected leakage from the storage reservoir. If a leak is found, the ability to rapidly deploy mitigation measures is needed. Here we use the TOUGHREACT code to develop a series of two-dimensional reactive transport simulations of the hydrogeochemical characteristics of a newly formed CO2 leak into an overlying aquifer. Using this model, we consider: (1) geochemical shifts in formation water indicative of a leak; (2) hydrodynamics of pumping wells in the vicinity of a leak; and (3) delivery of a sealant to a leak through an adjacent well bore.Our results demonstrate that characteristic shifts in pH and dissolved inorganic carbon can be detected in the aquifer prior to the breakthrough of supercritical CO2, and could offer a potential means of identifying small and newly formed leaks. Pumping water into the aquifer in the vicinity of the leak provides a hydrodynamic control that can temporarily mitigate the flux rate of CO2 and facilitate delivery of a sealant to the location of the caprock defect. Injection of a fluid-phase sealant through the pumping well is demonstrated by introduction of a silica-bearing alkaline flood, resulting in precipitation of amorphous silica in areas of neutral to acidic pH. Results show that a decrease in permeability of several orders of magnitude can be achieved with a high molar volume sealant, such that CO2 flux rate is decreased. However, individual simulation results are highly contingent upon both the properties of the sealant, the porosity-permeability relationship employed in the model, and the relative flux rates of CO2 and alkaline flood introduced into the aquifer. These conclusions highlight the need for both experimental data and controlled field tests to constrain modelling predictions

Development of indirect indicators for CO2 intrusion into freshwater

Cette étude porte sur l'impact des fuites de CO2 provenant d'un réservoir géologique de stockage de CO2 sur un aquifère d'eau douce. Elle se distingue des autres études, réalisées sur le même thème, par la recherche et l'application, depuis l'échelle du laboratoire jusqu'à celle d'un site pilote, de nouveaux outils de monitoring et d'approche isotopique destinés à la détection précoce de fuite de CO2. Afin de tester ces outils, des échantillons solides et liquides provenant de l'aquifèrestratégique de l'Albien du Bassin de Paris ont été prélevés, analysés et utilisés pour une étude expérimentale en batch. Cette expérience permet de contraindre et de comprendre précisément les interactions eau-roche-CO2 et les réponses isotopiques. Une application grandeur nature en Norvège a permis de mettre en place ce programme isotopique et de suivre l'évolution de la composition isotopique en distinguant les processus et phénomènes naturels et les processus reliés à l'injection de CO2. Ces deux cas d'étude appliqués au contexte de détection de fuite de CO2 ont permis de choisir les outils isotopiques les meilleurs comme indicateurs indirects de la présence de CO2, dans le cas particulier des systèmes étudiés. L'efficience de ces outils isotopiques réside dans l'enregistrement de la trace laissée par la présence de CO2 au cours d'interactions eau/roche/CO2. L'utilisation de tels outils nécessite une méthodologie rigoureuse abordée dans ce manuscrit et nécessite d'être adaptée aux spécificités des sites envisagés.This study deals with the impact of CO2 leakages out of geological storage into overlying freshwater aquifers. Compared to other existing studies, the major added value of this study lies, on the one hand, in the research of new monitoring tools and isotopic approach in the context of CCS aiming at early and sensitive detection of CO2 leakage and, on the other hand, in the application of these tools at the (limited) laboratory scale as well as at field scale. In order to test these tools, solid and liquid materials were sampled out of the major strategic drinking water Albian aquifer in the Paris Basin (France). We have then precisely characterized and used them within a batch experiment. This experiment yields interesting results which help understanding and constraining precisely the water-rock-CO2 interactions as well as the isotopic responses. A real scale application of the method was then performed in Norway. It was an opportunity to develop this isotopic program and to track the isotopic evolution composition, while differentiating the natural processes and the system response tothe CO2 injection. When applied to the detection of CO2 leakage context, the two case studies open the way for choosing the “best” isotopic tools as indirect indicators of CO2 presence in these specific systems. The efficiency of these isotopic tools comes from the recording of the CO2 footprint all along the water-rock-CO2 interactions. Using such tools imposes a rigorous methodology, which is tackled inthis manuscript. Furthermore, future application will require adapting to the specifics of a proposed site

Traçage des intrusions de CO2 dans les aquifères d'eau douce par les méthodes multi-isotopiques

This study deals with the impact of CO2 leakages out of geological storage into overlying freshwater aquifers. Compared to other existing studies, the major added value of this study lies, on the one hand, in the research of new monitoring tools and isotopic approach in the context of CCS aiming at early and sensitive detection of CO2 leakage and, on the other hand, in the application of these tools at the (limited) laboratory scale as well as at field scale. In order to test these tools, solid and liquid materials were sampled out of the major strategic drinking water Albian aquifer in the Paris Basin (France). We have then precisely characterized and used them within a batch experiment. This experiment yields interesting results which help understanding and constraining precisely the water-rock-CO2 interactions as well as the isotopic responses. A real scale application of the method was then performed in Norway. It was an opportunity to develop this isotopic program and to track the isotopic evolution composition, while differentiating the natural processes and the system response tothe CO2 injection. When applied to the detection of CO2 leakage context, the two case studies open the way for choosing the “best” isotopic tools as indirect indicators of CO2 presence in these specific systems. The efficiency of these isotopic tools comes from the recording of the CO2 footprint all along the water-rock-CO2 interactions. Using such tools imposes a rigorous methodology, which is tackled inthis manuscript. Furthermore, future application will require adapting to the specifics of a proposed site.Cette étude porte sur l'impact des fuites de CO2 provenant d'un réservoir géologique de stockage de CO2 sur un aquifère d'eau douce. Elle se distingue des autres études, réalisées sur le même thème, par la recherche et l'application, depuis l'échelle du laboratoire jusqu'à celle d'un site pilote, de nouveaux outils de monitoring et d'approche isotopique destinés à la détection précoce de fuite de CO2. Afin de tester ces outils, des échantillons solides et liquides provenant de l'aquifèrestratégique de l'Albien du Bassin de Paris ont été prélevés, analysés et utilisés pour une étude expérimentale en batch. Cette expérience permet de contraindre et de comprendre précisément les interactions eau-roche-CO2 et les réponses isotopiques. Une application grandeur nature en Norvège a permis de mettre en place ce programme isotopique et de suivre l'évolution de la composition isotopique en distinguant les processus et phénomènes naturels et les processus reliés à l'injection de CO2. Ces deux cas d'étude appliqués au contexte de détection de fuite de CO2 ont permis de choisir les outils isotopiques les meilleurs comme indicateurs indirects de la présence de CO2, dans le cas particulier des systèmes étudiés. L'efficience de ces outils isotopiques réside dans l'enregistrement de la trace laissée par la présence de CO2 au cours d'interactions eau/roche/CO2. L'utilisation de tels outils nécessite une méthodologie rigoureuse abordée dans ce manuscrit et nécessite d'être adaptée aux spécificités des sites envisagés

Impact of a CO2 leakage on groundwater quality. Influence of regional flow using reactive transport models.

Carbon Capture and Storage in deep and saline aquifers is one of the most hopeful technologies to reduce CO2 emissions into the atmosphere. However, CO2 leakages into shallow freshwater aquifers are a potential risk and potential impacts on groundwater have to be studied. A better understanding on how it could affect groundwater quality, aquifer minerals and trace elements is necessary to characterize a future storage site. Moreover, monitoring and remediation solutions have to be evaluated before storage operations. As part of the ANR project CIPRES, we present here reactive transport works. In a 3D model using ToughReact2, we perform different CO2 leakage scenarios in a confined aquifer, considering both brines and carbon dioxide gas. Our modeling works are based on the Albian aquifer, a strategic water resource for the Paris basin. This layer is the main aquifer overlying the Dogger deep saline aquifer. We consider one groundwater and rocks chemistry of the Albian aquifer composed by the Albian green sand (Quartz, Calcite, Glauconite , Kaolinite) at 700 m deep. The geochemical model was elaborated from experimental data performed in previous study (Humez, 2012). The aquifer consists in a mesh, divided roughly in 20000 cells making a 60 m thick and a 500 m large layer. Furthermore, cells are subdivided near the leakage point to consider local phenomena (secondary precipitation, kinetics, sorption/desorption...). We highlight the importance of surface complexation on trace element transport (As, Zn and Ni). Moreover, we distinguish different geochemical behavior (CO2 plume shape, secondary precipitation of siderite or chalcedony, desorption...) according to different horizontal flow rate influenced directly by the hydrodynamics (regional gradient). Understanding how geochemical reactions and regional flows influence water chemistry, allows to ascertain measurement monitoring and verification plan and remediation works in case of leak considering a given location

Soil gas flux measurements as part of environmental baseline assessment

International audienceNatural gas seeps provide a unique opportunity for testing techniques and strategies of environmental baseline assessment (EBA) for exploration or exploitation activities of conventional and unconventional methane. We report field acquisitions performed at a gas seep in the French Alps where thermogenic, CH4-dominated (up to 85% vol.) and CO 2-rich (up to 11.5 % vol.) gas emanates over a localized 8x4 m emission area with complex geometry (Gal et al., 2016) that characterizes many naturally occurring gas vents (e.g. Etiope et al., 2010). We tested a portable system of in-situ soil gas flux measurements, combining an accumulation chamber and a monitoring system, recording CH4 and CO 2 enrichments as well as O 2 depletion over 3 minutes, the typical duration of soil flux measurements. Methane fluxes have been quantified on 70 monitoring points emplaced along a 2x1 m mesh grid. The potential time evolution of the CH4 and CO 2 emission has been assessed through complementary soil gas concentration measurements at 1 m depth. Only minor changes of the location of the emitting points with respect to previous measurements have been observed. Correlations of CO 2 , O 2 and CH4 indicate distinct processes of CH4-oxidation in the area surrounding the main CH4-vent and in the vent itself. The most active part of the gas vent only exhibits high CH4 fluxes whereas adjacent areas show moderate to high CH4 and CO 2 fluxes and more distal areas are only characterized by a CO 2 flux. Multi-gas flux measurements in the vicinity of a seep or supposed leak is an efficient and straightforward onsite method to be integrated in EBA, but spatial extension and resolution of survey grids will depend much on the expected scale of impact of industrial point sources (exploration/exploitation wells). Natural fluxes can be addressed both for methane and CO 2 and reduction-oxydation processes assessed through correlation with O 2. Other vents in similar geological positions in the French subalpine chains on a vast transect from the Swiss border to the Provence were identified, based on historical records, and some of them rediscovered and measured

A geochemical and multi-isotope modeling approach to determine sources and fate of methane in shallow groundwater above unconventional hydrocarbon reservoirs

International audienceDue to increasing concerns over the potential impact of shale gas and coalbed methane (CBM) development on groundwater resources, it has become necessary to develop reliable tools to detect any potential pollution associated with hydrocarbon exploitation from unconventional reservoirs. One of the key concepts for such monitoring approaches is the establishment of a geochemical baseline of the considered groundwater systems. However, the detection of methane is not enough to assess potential impact from CBM and shale gas exploitation since methane in low concentrations has been found to be naturally ubiquitous in many groundwater systems. The objective of this study was to determine the methane sources, the extent of potential methane oxidation, and gas-water-rock-interactions in shallow aquifers by integrating chemical and isotopic monitoring data of dissolved gases and aqueous species into a geochemical PHREEQC model. Using data from a regional groundwater observation network in Alberta (Canada), the model was designed to describe the evolution of the concentrations of methane, sulfate and dissolved inorganic carbon (DIC) as well as their isotopic compositions (δ34SSO4, δ13CCH4 and δ13CDIC) in groundwater subjected to different scenarios of migration, oxidation and in situ generation of methane. Model results show that methane migration and subsequent methane oxidation in anaerobic environments can strongly affect its concentration and isotopic fingerprint and potentially compromise the accurate identification of the methane source. For example elevated δ13CCH4 values can be the result of oxidation of microbial methane and may be misinterpreted as methane of thermogenic origin. Hence, quantification of the extent of methane oxidation is essential for determining the origin of methane in groundwater. The application of this model to aquifers in Alberta shows that some cases of elevated δ13CCH4 values were due to methane oxidation resulting in pseudo-thermogenic isotopic fingerprints of methane. The model indicated no contamination of shallow aquifers by deep thermogenic methane from conventional and unconventional hydrocarbon reservoirs under baseline conditions. The developed geochemical and multi-isotopic model describing the sources and fate of methane in groundwater is a promising tool for groundwater assessment purposes in areas with shale gas and coalbed methane development

CO2-water-mineral reactions during CO2 leakage into glauconitic sands: geochemical and isotopic monitoring of batch experiments

International audienceThe assessment of environmental impacts of carbon dioxide geological storage requires the investigation of the potential CO2 leakages into fresh groundwater reserves. The Albian aquifer of the Paris Basin was chosen as a case of study because i) the Paris Basin contains deep saline Jurassic and Triassic aquifers identified as targets by the French national program of CO2 geological storage and ii) the Albian aquifer is a deep freshwater resource of strategic national importance, above the Jurassic and Triassic formations. An experimental and a geochemical modelling approach were carried out in order to better understand the rock-water-CO2 interactions with two main objectives: to assess the evolution of the chemistry of the formation water and of the mineralogy of the solid phase during the interaction and to design a monitoring program for freshwater resources. The main focus is to select and develop suitable indirect indicators of the presence of CO2 in the aquifer. We present here the experimental results, which combines both major and trace elements and isotopic tools, some of them new in the CCS field. Batch reactors with a liquid/solid ratio of 10 made of appropriate materials (PTFE, stainless steel) were equipped with simultaneous controls on several parameters (pH measurement, gas phase composition, pressure, tightness. . . ) after CO2 injection (PCO2= 2 bar; room temperature). Ten reactors were run simultaneously, over pre-determined durations of CO2-water-rock interaction (1, 7, 15 and 30 days). During the batch experiment, we observed major changes in several chemical parameters due to the CO2 injection. A sharp drop in pH from 6.6 to 4.9 was noticeable, immediately after the injection, due to CO2 dissolution in the water phase. Alkalinity varies from 1.3 mmol.L-1 in the initial water to 2.0 mmol.L-1 at the end of the 1-month experiment. Four types of ion behaviors are observed: (1) calcium, silicon and magnesium concentrations increase during the 1-month experiment; (2) dissolved iron strongly decreases immediately after CO2 injection; (3) potassium, sodium and fluorine concentrations increase at the start of CO2 injection and then stabilize to levels higher than the pre-injection concentrations, (4) chlorides and sulfates are stable. These variations indicate dissolution/precipitation and surface reactions involving mineral phases such as glauconite, siderite/iron hydroxide. The experimental results were interpreted and the geochemical mechanisms involved were included in geochemical modeling using PHREEQC, an essential step to quantify the overall effect of the combined individual reactions and processes. These mechanisms were corroborated with isotopic ratio variations. E.g. the variations of δ13CDIC (from -15.7 ﰐ to -21 ﰐ vs. PDB) cannot be explained solely by the CO2 dissolution, and indicate additional chemical processes. Likewise, shifts of δ11B towards more negative values stress the implication of the glauconitic minerals, mainly B-bearing phase in the system. These experimental results, and their numerical simulation, are promising for the development of our indirect geochemical and isotopic monitoring technique