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 in a shallow aquifer - Observed changes in case of small release

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 but potential leakage monitoring is required by legislation, as e.g. the EU Directive relative to Geological Storage of CO2. To ensure that the storage will be permanent and safe for the environment and human health, the legislation require that the CCS operators monitor the injection, the storage complex and if needed the environment to detect any CO2 leakage and its hazardous effects on the environment. Various monitoring methods are available for the monitoring of CO2 storage sites and the environment as listed by the IEA-GHG and the monitoring selection tool. Geophysical based methods have a greater area of investigation but may suffer from insufficient sensitivities to detect small leakages. At the opposite, geochemical monitoring methods may have insufficient investigation area but may be able to detect more subtle changes even if monitoring in deep environments is not straightforward. Leakage detection is not yet well constrained and research efforts and tests are required to gain confidence into monitoring strategies. In the framework of the CIPRES project, funded by the French Research Agency, a shallow CO2 release experiment has been performed in October 2013 in a chalk aquifer from the Paris basin. The Catenoy site has been characterised since March 2013 through several wells set on a straight line oriented along the local flow (see Gombert et al., this conference). Such an experiment is designed to gain confidence in leakage detection in subsurface environments by understanding processes and principles governing seepage occurrence. Contrary to other experiments such as ZERT or CO2FieldLab ones, where gaseous CO2 was injected directly in the water, the injection was done with water saturated with CO2 at atmospheric pressure. 10 m3 of water were pumped from the aquifer, then saturated with 20 kg of food-grade CO2 and injected during 40 hours between 12 and 25 m depth. Daily monitoring of soil gases and water was performed during injection and post-injection phases (2 weeks duration) in the area previously delimited by a tracer test. The aim is to determine if geochemical methods are accurate enough to allow detecting small release in shallow environments. If successful, such an experiment can help to gain confidence in leakage detection. As expected, no change was noticed in the unsaturated zone. The shape of gas concentrations distribution at the surface (CO2, O2, N2, 4He, 222Rn) observed during the injection is strictly similar to the repartition of gas species observed since March 2013. The main process observed is respiration and no change linked to the injection was highlighted, only seasonal effects. Slight changes were observed in the saturated zone. The water was collected at 15 m deep excepted for one stratified borehole where water was sampled at 15 and 18 m. The pH of the injected water was lower (mean value: 5.3±0.1) than the initial pH of the aquifer (7.1-7.2) due to CO2 dissolution. Only two monitoring boreholes set 10 m and 20 m downstream from the injection well may be considered as influenced by the experiment. A probable enrichment in HCO3 linked to interaction of the CO2 saturated water with chalk was noticed, with an enrichment close to +8 to +10% of the initial value. For one borehole the pH value remained nearly stable in relation with pH buffering and in the other borehole a slight decrease was observed (-0.1 to -0.15 pH unit). However this decrease is significant as it is above the instrumental uncertainty of the electrodes. In addition, a slight increase of the electrical conductivity was noticed but it did not exceed +6% compared to baseline data. Such slight changes in the physico-chemical parameters are related to small variations in dissolved elements. Apart from HCO3, the other major ion affected by CO2-water rock-interaction is Ca as the aquifer is mainly composed by calcite. Concentrations increases by +8 to +9% whose amplitude is in agreement with the increase of HCO3. Trace elements were also little affected, the main change concerned Sr (+8 to +10% increase). Modifications occurring during this CO2 release experiment have small amplitude as expected but these results highlight that geochemical methods are able to detect small leakages. Consequently, effects were noticed only during a short period of time. It is not possible to determine if all the injected CO2 has migrated downwards in the direction of flow or if partial lateral migration has occurred, but post-injection monitoring and boreholes logging 12 days after the stop of injection did not reveal any discrepancy in the water columns. On the other hand, the magnitude of the pH change is consistent with the behaviour of the co-injected tracer (dilution ratio ~30). In the perspective of getting more information on the remobilisation of trace metal elements, a push-pull test will be performed in 2014 on the basis of the learning of this first experiment

Hydrochemical impatcs of CO2 leakage on fresh groundwater; A field scale experiment

One of the questions related to the emerging technology for Carbon Geological Storage concerns the risk of CO2 migration beyond the geological storage formation. In the event of leakage toward the surface, the CO2 might affect resources in neighbouring formations (geothermal or mineral resources, groundwater) or even represent a hazard for human activities at the surface or in the subsurface. In view of the preservation of the groundwater resources mainly for human consumption, this project studies the potential hydrogeochemical impacts of CO2 leakage on fresh groundwater quality. One of the objectives is to characterize the bio-geochemical mechanisms that may impair the quality of fresh groundwater resources in case of CO2 leakage. To reach the above mentioned objectives, this project proposes a field experiment to characterize in situ the mechanisms having an impact on water quality and the CO2-water-rock interactions and also to improve the monitoring methodology by controlled CO2 leakage in shallow aquifer. The tests ran on an experimental site in the chalk formation of the Paris Basin. The site is equipped with an appropriate instrumentation and previously characterized (8 piezometers, 25 m deep and 4 piezairs 11 m deep). The injection test was preceded by 6 months of monitoring in order to characterize hydrodynamics and geochemical baselines of the site (groundwater, vadose and soil). Leakage into groundwater is simulated via the injection of a small quantity of food quality CO2 (~20 kg dissolved in 10 m3 of water) in the injection well at a depth of about 20 m. A plume of dissolved CO2 is formed and moves downward according to the direction of groundwater flow and probably by degassing in part to the surface. During the injection test, hydrochemical monitoring of the aquifer is done in situ and by sampling. The parameters monitored in the groundwater are the piezometric head, temperature, pH and electrical conductivity. Analysis on water samples provide chemical elements (major, minor and trace metals), dissolved gases, microbiological diversity and isotopes (13C). The evolution of the composition of the groundwater in terms of major elements, trace elements and isotope signatures is interpreted in terms of geochemical mechanisms, and the water-rock-CO2 interactions are characterised. Modification of the chemical composition of the water in the aquifer due to CO2 injection is assessed in term of groundwater quality i.e. metal element release and the possibility of exceeding references and quality of water for human consumption. One outcome of the CIPRES project will be to highlight mechanisms that can impact groundwater quality when a CO2 leakage occurs and to propose recommendations to prevent or/and eliminate negative effects and any risks to the environment and human health. This project is partially funded by the French Research Agency (ANR)

CO2 leakage in a shallow aquifer – Observed changes in case of small release

AbstractGeological 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 but potential leakage monitoring is required by legislation, as e.g. the EU Directive relative to Geological Storage of CO2. To ensure that the storage will be permanent and safe for the environment and human health, the legislation require that the CCS operators monitor the injection, the storage complex and if needed the environment to detect any CO2 leakage and its hazardous effects on the environment. Various monitoring methods are available for the monitoring of CO2 storage sites and the environment as listed by the IEA-GHG and the monitoring selection tool. Geophysical based methods have a greater area of investigation but may suffer from insufficient sensitivities to detect small leakages. At the opposite, geochemical monitoring methods may have insufficient investigation area but may be able to detect more subtle changes even if monitoring in deep environments is not straightforward. Leakage detection is not yet well constrained and research efforts and tests are required to gain confidence into monitoring strategies.In the framework of the CIPRES project, funded by the French Research Agency, a shallow CO2 release experiment has been performed in October 2013 in a chalk aquifer from the Paris basin. The Catenoy site has been characterised since March 2013 through several wells set on a straight line oriented along the local flow (see Gombert et al., this conference). Such an experiment is designed to gain confidence in leakage detection in subsurface environments by understanding processes and principles governing seepage occurrence. Contrary to other experiments such as ZER

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 guide for assessing the potential impacts on ecosystems of leakage from CO2 storage sites

Evidence to date indicates that leakage is of low probability if site selection, characterisation and storage project design are undertaken correctly. In Europe, the Storage Directive (EC, 2009) provides a legislative framework, implemented by Member States, which requires appropriate project design to ensure the storage of CO2 is permanent and safe. However, it is incumbent on storage site operators to demonstrate an understanding of the potential impacts on surface ecosystems should a leak occur. The RISCS (Research into Impacts and Safety in CO2 Storage) project has produced a Guide to potential impacts of leakage from CO2 storage (the ‘Guide’). RISCS assessed the potential effects of CO2 leakage from geological storage on both onshore and offshore near-surface ecosystems and on potable ground water. This assessment was achieved through laboratory and field experiments, through observations at sites of natural CO2 seepage and through numerical simulations. The Guide summarises some of the key findings of the project. The Guide provides information on the best approaches to evaluate potential impacts of hypothetical leakage from CO2 storage sites and to provide guidance on appraising these impacts. This information will be relevant to regulators and operators in particular, but also to other stakeholders who are concerned with CO2 storage, such as national and local governments, and members of the public

Selection, Instrumentation and Characterization of a Pilot Site for CO2 Leakage Experimentation in a Superficial Aquifer

AbstractCO2 geological storage is one of the options for mitigation of GHG emissions into the atmosphere. Although storage is provided for several millennia, leakage can occur. Therefore the risk that the fugitive CO2 reaches a shallow aquifer cannot be excluded [1]. That is why the consortium launched the research program CIPRES, funded by the French Research Agency, concerning the potential impacts of CO2 leakage on groundwater quality. This program includes the realization of a shallow CO2 release experiment in a carbonated aquifer and its monitoring in the saturated and unsaturated zones, the soil and the soil-atmosphere interface. The experimentation consists in drilling a well into the aquifer, injecting dissolved CO2 in water [2] and tracking its impact downstream. Prior to this experiment, a site had to be selected, instrumented and characterized.Hydrogeological target is the Paris basin chalk which is the largest French aquifer. The selected area is a large parcel, formerly cultivated in intensive monoculture but left fallow for several years, located in Catenoy (Oise) about 50km north of Paris. The geological log shows the chalk is covered by 6-7 m of sands but water table is located at 12-13 m depth, i.e. integrally in the chalk strata.The site has been equipped with 10 wells to characterize the groundwater flow (hydraulic gradient ∼5 10-3). 6 wells are aligned in the groundwater flow direction: the PZ2, planned for CO2 injection, the PZ1 located 20 m upstream and 4 monitoring wells located downstream between 10 and 60 m from PZ2. There are also 4 lateral piezometers located near (PZ7, PZ8) and far (PZ9, PZ10) from the injection site: they are dedicated to the lateral plume. These 25 m depth wells are equipped with tubing fully slotted in the chalk. Alongside, 4 wells dedicated to gas monitoring in unsaturated zone have been drilled at 11m depth.To characterize the site, the following operations were performed prior to the CO2 injection between March and September 2013:•pump test into PZ2 to estimate the hydraulic conductivity (10-3 m.s-1) and the storage coefficient (1.6%); the hydraulic conductivity is higher in the first 3 m of saturated zone (∼5 10-3 m.s-1);•hydrogeochemical baseline with monthly water analysis in each well (physicochemical parameters, major and minor ions, metallic trace elements); electrical conductivity is 714μs.cm-1 and groundwater has a calcium-bicarbonated facies with high nitrate concentration (45mg.l-1) and low-level presence of trace metals;•gas baseline with continuous O2 and CO2 measurement in vadose trough 11 m depth boreholes and measurements campaigns to determine gas concentration in the soil and gas flux on the surface;•flowmeter heatpulse logging at PZ2, PZ3 and PZ4 in static and dynamic conditions; only the area situated from 15 m to 20 m depth is productive and a vertical natural downflow is measured in PZ3 (∼1-2mm.s-1) and PZ4 (1cm.s-1); furthermore, no flow is measured from 20 to 25 m depth; this confirms the vertical anisotropy of the chalky aquifer;Following this experiments, a tracer test has been done in June 2013 from PZ2 with fluorescent tracer (amino-acid G) and a dissolved gas (He), in the way to calibrate the future CO2 injection and its monitoring. 2 m3 of water from the aquifer were pumped the day before the injection and stored in tanks. Then 2kg of tracer were dissolved and water was saturated with He. This water was injected into the PZ2 the next day during 8h. The monitoring was conducted for a month by water sampling, tracer and He analyzes. The peak of fluorescent tracer arrived at the 2nd day following injection in the PZ4 (20 m downstream) but only one week later in the PZ3 (10 m downstream), due to the site anisotropy. Low He concentrations have been detected in the unsaturated zone of PZ4 before PZ3, in correlation with tracer migration.The main result is the existence of an high aquifer anisotropy in such a small area: i) the first 3 m of the saturated zone shows a higher permeability and the last 5 m a lower one, ii) the tracer arrives quickly and with higher concentration at PZ4 located 10 m farther than PZ3. However, the dilution ratio is rather important and may induce, during CO2 leakage experimentation, a slight pH decrease at the downstream wells: in order to increase the impact of the CO2 leakage, we have therefore planned to inject a higher volume (10 m3) of CO2 saturated water

Etude hydrogéochimique de la mobilité de polluants inorganiques dans des sédiments de curage mis en dépôt: expérimentations, étude in situ et modélisations

In order to maintain navigation channels, periodic dredging of the bed sediments is carried out. In industrialised areas, these sediments may have been contaminated by discharged effluents. Therefore, significant quantities of contaminated sediments may be deposited, generally on the banks of the watercourse. Consequently, physicochemical alteration of these sediments, especially oxidation, plays a significant role in determining the mobility and hence eventual distribution of these contaminants. These mobilised toxic elements may represent a hazard for the soils and the aquifers in the vicinity of the deposited sediments. The objective of this study was to characterize and model the mechanisms responsible for the mobilization of the inorganic pollutants in the studied sediment. Both laboratory experiments and field studies were performed. The laboratory experiments consisted of performing leaching test under controlled and simplified conditions, on sediments contaminated with Pb, Zn and Cd, sampled after 5 years of ageing. To characterize both the mobile components (major elements and metals) and the mechanisms controlling their mobility, the leaching tests were performed as both static tests in the form of batch kinetic desorption tests and dynamic tests. The dynamic tests were performed as both batch, in the form of shaking cascade test and in column in order to account for the hydrodynamic factors. All the tests found that zinc and cadmium were reversibly bound to the sediment and underlined the importance of calcium concentration in determining their mobility by ionic exchange. After characterising both the composition of the sediment and the mechanisms controlling the metals motilities, a conceptual model of the sediment was devised in order to simulate the experiments. The model accounted for buffering capacity, mineral dissolution kinetics and ionic exchange. Simulations performed using the geochemical code CHESS gave good agreement with the results obtained from the batch experiments. The reactive transport code HYTEC was used to simulate the column experiments, using the same reaction parameters as for the batch simulations. The field studies were primarily related to the characterization of the sediment deposit. The thirty year old deposit contains a subsurface layer of very highly contaminated materials (Pb, Zn, Cd, As). On the surfaces of the deposit, oxidation of the sediment with precipitation of secondary phases such as carbonates and sulphates as well as (hydr)oxides is evident. However, due to the thickness of the deposit, the major phases of the system are sulphides. A piezometric study of the deposit identified three zones, differing in their texture, total metals content, hydrochemistry and hydrogeology. From these data in combination with geochemical modelling, it was possible to determine the mechanisms responsible for controlling the mobility of the metals. In order to evaluate the environmental impact of the sediment deposits the study also considered the subjacent horizons and aquifer. The high sorption capacity of the subjacent horizons was fount to be responsible for the retention of the investigated metals (Pb, Zn, Cd). Simulations of both saturated and unsaturated zones were performed by HYTEC to reproduce the site hydrogeology, coupled with a geochemical model accounting for ionic exchange and mineral precipitation. These simulations were used to predict the infiltration of metals into the subjacent aquifer. Moreover a survey of this aquifer was set up and confirmed the absence of contamination. Lastly, hydrogeological simulations were performed to investigate tracer dispersion in the aquifer, accounting for the local hydrogeology.L'entretien des voies navigables nécessite le curage régulier des cours d'eau. Dans les environnements industriels et miniers, les sédiments peuvent être contaminés par divers polluants. Dans le cas où ces derniers s'avèrent être mobiles, l'entreposage des sédiments de curage peut présenter un risque pour l'environnement. Cette étude a porté sur la caractérisation de la mobilité des métaux et des métalloïdes dans les sédiments mis en dépôt. Dans un premier temps, elle a été menée à l'échelle du laboratoire où des essais de lixiviation, en batch et en colonne, ont mis en évidence que le zinc et le cadmium sont mobilisables. L'interprétation des données a permis de déterminer les principales phases et les mécanismes (dissolution cinétique, échange ionique) susceptibles de contrôler la solution. Ces hypothèses ont permis d'élaborer un système simplifié du sédiment étudié qui, intégré aux codes géochimiques CHESS et HYTEC, a permis de reproduire l'ensemble des essais expérimentaux. La modélisation a souligné le rôle majeur du calcium en solution, sur la mobilité des métaux disponibles sous forme échangeable (Zn, Cd et Mn). La mobilité des contaminants inorganiques a également été appréhendée à l'échelle du terrain. Le site étudié contient des sédiments, fortement contaminés, mis en dépôt il y a 30 ans. Cette étape a consisté à caractériser les interactions eau/sédiment au sein du matériel entreposé, notamment par des calculs de spéciation. Puis la dissémination des métaux (Pb, Zn et Cd) vers les couches et l'aquifère sous-jacents au dépôt a été évaluée. Pour cela, des essais de sorption ont été réalisés et un suivi de la qualité des eaux de la nappe de la Craie a été mis en place autour et sous le site. Cette phase a été complétée par une phase de modélisation hydrogéochimique: en prenant en compte les écoulements en zone saturée et non saturée et les mécanismes géochimiques tels la précipitation et l'échange ionique, il a été possible d'évaluer que les temps de transfert des métaux, entre le dépôt contaminé et l'aquifère de la Craie, sont très lents. Ceci s'explique, notamment, par un pouvoir de rétention important des couches sous-jacentes au dépôt. Cette étude a montré qu'après leur mise en dépôt, les sédiments sont susceptibles de libérer les métaux qu'ils contiennent. Ces métaux, sont rapidement immobilisés sous forme secondaires telles les sulfates, les carbonates, les oxydes mais également sous forme échangeable. Ce mécanisme de rétention est réversible, l'immobilisation des métaux n'est donc pas définitive, mais il contribue cependant à retarder la dissémination des métaux dans l'environnement. Ainsi, à l'heure actuelle, aucune pollution de la nappe phréatique n'a été observée suite à la mise en dépôt de ces sédiments, même fortement contaminés

Synthèse sur les impacts potentiels du stockage géologique du CO 2 sur les ressources en eau souterraines

International audienceAfin de réduire les émissions atmosphériques de CO 2 provenant des activités humaines, des stratégies novatrices de stockage doivent être appliquées au dioxyde de carbone (CO 2 ) produit par la combustion de combustibles fossiles. Parmi les techniques de stockage actuellement proposées, le captage, le transport et le stockage du CO 2 sont proposés. Le stockage géologique du CO 2 consiste à injecter du CO 2 dans les formations géologiques profondes, par exemple dans les réservoirs de pétrole et de gaz épuisés, les formations salines profondes et des veines de charbon inexploitables. L‟objectif est de stocker de grande quantité de CO 2 et de le maintenir isolé de l‟atmosphère durablement.La technologie du captage et stockage de CO 2 (CSC) se doit également d‟avoir un impact minimal et acceptable sur la sécurité et la santé humaine, les ressources du sous-sol dont les eaux et sur l‟environnement. En France, le stockage principalement envisagé dans des formations aquifères profondes dont les eaux sont impropres à leur utilisation par l‟homme. Un stockage sûr et permanent est donc en mesure de respecter les conditions de sécurité pour la santé humaine et l‟environnement. Il convient néanmoins de s‟assurer que les futurs sites de stockage soient suffisamment bien caractérisés et surveillés pour éviter toutes défaillances ou impacts susceptibles notamment d‟altérer les ressources en eauxsouterraines.Ce rapport a pour objectif de décrire les impacts du stockage du CO2 sur les eaux souterraines et se focalise sur le stockage en aquifère salin profond