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Carbon Capture and Storage (CCS) is a suite of technologies available to directly reduce carbon dioxide (CO2) emissions to the atmosphere from fossil fuelled power plants and large industrial point sources. For a safe deployment of CCS it is important that CO2 injected into deep geological formations does not migrate out of the storage site. Characterising and understanding possible migration mechanisms and pathways along which migration may occur is therefore crucial to ensure secure engineered storage of anthropogenic CO2. In this thesis naturally occurring CO2 accumulations in the subsurface are studied as analogue sites for engineered storage sites with respect to CO2 migration pathways and mechanisms that ensure the retention of CO2 in the subsurface. Geological data of natural CO2 reservoirs world-wide has been compiled from published literature and analysed. Results show that faults are the main pathways for migration of CO2 from subsurface reservoirs to the surface and that the state and density of CO2, pressure of the reservoir, and thickness of the caprock influence the successful retention of CO2. Gaseous, low density CO2, overpressured reservoirs, and thin caprocks are characteristics of insecure storage sites. Two natural CO2 reservoirs have been studied in detail with respect to their fault seal properties. This includes the first study of how fault rock seals behave in CO2 reservoirs. It has been shown that the bounding fault of the Fizzy Field reservoir in the southern North Sea can with hold the amount of CO2 trapped in the reservoir at current time. A initially higher gas column would have led to across fault migration of CO2 as the fault rock seals would not have been able to withhold higher pressures. Depending on the present day stress regime the fault could be close to failure. At the natural CO2 reservoir of St. Johns Dome, Arizona, migration of CO2 to the surface has been occurring for at least the last 500 ka. Fault seal analysis shows that this migration is related to the fault rock composition and the orientation of the bounding fault in the present day stress field. Using the U-Th disequilibrium method the ages of travertine deposits of the St. Johns Dome area have been determined. The results illustrate that along one fault CO2 migration took place for at least 480 ka and that individual travertine mounds have had long lifespans of up to ~350 ka. Age and uranium isotope trends along the fault have been interpreted as signs of a shrinking CO2 reservoir. The amount of CO2 calculated to have migrated out of the St. Johns Dome is up to 113 Gt. Calculated rates span from 5 t/yr to 30,000 t/yr and indicate that at the worst case large amounts of CO2 can migrate rapidly from the subsurface reservoir along faults to the surface. This thesis highlights the importance of faults as fluid pathways for vertical migration of CO2. It has been also shown that they can act as baffles for CO2 migration and that whether a fault acts as pathway or baffle for CO2 can be predicted using fault seal analysis. However, further work is needed in order to minimise the uncertainties of fault seal analysis for CO2 reservoirs.

Global energy consumption will increase in the next decades and it is expected to largely rely on fossil fuels. The use of fossil fuels is intimately related to CO₂ emissions and the potential for global warming. Geological CO₂ storage aims to mitigate the global warming problem by sequestering CO₂ underground. Coupled hydro-chemo-mechanical phenomena determine the successful operation and long term stability of CO₂ geological storage. This research explores various coupled phenomena, identifies different zones in the storage reservoir, and investigates their implications in CO₂ geological storage. Spatial patterns in mineral dissolution and precipitation are examined based on a comprehensive mass balance formulation. CO₂-dissolved fluid flow is modeled using a novel technique that couples laminar flow, advective and diffusive mass transport of species, mineral dissolution, and consequent pore changes to study the reactive fluid transport at the scale of a single rock fracture. The methodology is extended to the scale of a porous medium using pore network simulations to study both CO₂ reservoirs and caprocks. The two-phase flow problem between immiscible CO₂ and the formation fluid (water or brine) is investigated experimentally. Plug tests on shale and cement specimens are used to investigate CO₂ breakthrough pressure. Sealing strategies are explored to plug existing cracks and increase the CO₂ breakthrough pressure. Finally, CO₂-water-surfactant mixtures are evaluated to reduce the CO₂-water interfacial tension in view of enhanced sweep efficiency. Results can be used to identify optimal CO₂ injection and remediation strategies to maximize the efficiency of CO₂ injection and to attain long-term storage.

Une des solutions visant à atténuer le changement climatique est le stockage géologique de CO2 dans des aquifères salins ou des réservoirs de pétrole - ou de gaz - en fin de vie. L'étanchéité des puits d'injection de CO2 doit cependant être garantie pour des durées séculaires. En théorie, le ciment coulé après le forage du puits entre le cuvelage en acier et la formation rocheuse a pour vocation de rétablir l'étanchéité naturelle entre les différentes couches géologiques traversées par le puits. Une fois pris, le ciment constitue une interface de quelques centimètres d'épaisseur entre la roche et le cuvelage. Cette interface cimentaire apparaît comme le point le plus critique vis-à-vis de l’étanchéité et du confinement CO2. En effet, le CO2 injecté étant sec et sous pression, la zone « proche puits » au niveau du point d'injection va s'assécher progressivement et s'étendre vers le toit du réservoir au fur et à mesure que le CO2 est injecté. L’interface se retrouve alors soumise à de fortes sollicitations hydriques induisant un séchage et de fortes contraintes mécaniques (réservoir de CO2). On s'attend donc à ce que ces contraintes engendrées par les incompatibilités de déformation entre les différents matériaux et les pressions d'injection soient par conséquent à l'origine d'une fissuration le long de l'interface et dans la zone proche puits. Dans ce contexte, nous nous intéressons à la manière dont le formalisme de la poromécanique doit être étendu en utilisant une approche énergétique de la mécanique de la rupture pour décrire ces phénomènes induit par l'injection de fluide sous pression dans un milieu poreux confiné. L’idée originale de cette démarche est de pouvoir décrire des écoulements couplés dans un milieu poreux élastique déformable et endommageable induits par une action combinée des gradients hydrauliques et de pressions imposés simultanément. Ce modèle devrait permettre une bonne compréhension, ainsi qu'une analyse théorique, de la physique mise en jeu dans ces processus complexes de transport pouvant provoquer la dégradation d’une structure. L’implémentation numérique s'appuie sur une discrétisation éléments finis standard et sur l’adaptation d’un modèle d'eigenerosion pour simuler l’apparition de fissures. / Underground carbon dioxyde (CO2) storage operation in deep geological formation like saline aquifers or gas reservoirs is considered to be a prospective solution to reduce the emission of greenhouse gases into the atmosphere. However CO2 sealing injection has to be assured for centuries. Once setting, the cement is a few centimeters thickness interface between the rock and the casing. This cementeous interface appears as the most critical point for the sealing and containment of CO2. A continuous stream of CO2 being injected into reservoir rock formation will cause in a region around the injection water desaturation and drying shrinkage of the reservoir and the cement paste and potentially hydraulic fracture. Therefore, the moisture balance with the CO2 reservoir induces water desaturation and drying shrinkage. Some local stresses are then expected because of the strain incompatibility between the cement and the steel casing and the high pressures levels. These stresses may result in a cracking process along the interface and in a secondary cracks network. In this context, we investigate how the poromechanical theory should be extended using a energy approach framework to describe the fracture mechanic induced by the fluid injection in a porous medium. The original idea of this approach consists in deriving the poro-mechanical equations introducing explicitly the multiphase flow. This model, aims at describing coupled flows in a damageable elastic porous medium, due to the combined influence of hydraulic and pressure gradients simultaneously imposed. The numerical implementation is based on a standard finite element discretization and adaptation of a eigenerosion model to simulate cracking.

In an effort to mitigate carbon dioxide (CO2) emissions in the atmosphere, the Southeast Offshore Storage Resource Assessment (SOSRA) project has for objective to identify geological targets for CO2 storage in two main areas: the eastern part of the Gulf of Mexico and the Atlantic Ocean subsurface. SOSRA's second objective is to estimate the geological targets' capacity to store up to 30 million metric tons of CO2 each year with an error margin of ±30%. As part of this project, the research presented here focuses on the outer continental shelf of North Carolina and its potential for the deployment of large-scale offshore carbon storage in the near future. To identify geological targets, workflow followed typical early oil and gas exploration protocols: collecting existing datasets, selecting the most applicable datasets for reservoir exploration, and interpreting datasets to build a comprehensive regional geological framework of the subsurface of the outer continental shelf. The geomodel obtained can then be used to conduct static volumetric calculations estimating the storage capacity of each identified target. Numerous uncertainties regarding the geomodel were attributed to the variable coverage and quality of the geological and geophysical data. To address these uncertainties and quantify their potential impact on the storage capacity estimations, dynamic volumetric calculations (reservoir simulations) were conducted. Results have shown that, in this area, both Upper and Lower Cretaceous Formations have the potential to store large amounts of CO2 (in the gigatons range). However, sensitivity analysis highlighted the need to collect more data to refine the geomodel and thereby reduce the uncertainties related to the presence, dimensions and characteristics of potential reservoirs and seals. Reducing these uncertainties could lead to more accurate storage capacity estimations. Adequate injection strategies could then be developed based on robust knowledge of this area, thus increasing the probability of success for carbon capture and storage (CCS) offshore projects in North Carolina's outer continental shelf. / Doctor of Philosophy / Since the industrial revolution, a significant increase in the anthropogenic emissions of greenhouse gases has been observed worldwide. The rise in concentration of these gases in the atmosphere, specifically carbon dioxide (CO₂), has been linked to an increase in the average temperature on Earth, what is commonly known as global warming. To mitigate the emission of anthropogenic CO₂ in the atmosphere and consequently limit its impact on Earth’s climate, Carbon Capture and Storage projects (CCS) have been developed on various scales. In this type of project, CO₂ is captured from an emitting source (e.g., power plants), then transported via pipelines and stored in deep geological formations. In the United States, onshore CCS projects have demonstrated the technical feasibility of such projects. However, controversies associated with public acceptance and mineral ownership make expansive onshore CCS project development complicated. For these reasons, the U.S. Department of Energy (DOE) has been investigating offshore locations for the deployment of large-scale CCS projects. Southeast Offshore Storage Resource Assessment (SOSRA) is a project sponsored by the U.S. DOE to assess the storage potential of the eastern part of the Gulf of Mexico and the Atlantic Ocean as a first step towards the development of large-scale offshore storage of CO₂. The state of North Carolina was identified as an adequate candidate for CO₂ offshore storage due to its location on the Atlantic coast and its elevated CO₂ emissions from the power plants on its coastal plains. However, as exploration conducted on the outer continental shelf of North Carolina has been minimal, published information regarding the subsurface of this area remains limited to this date. To ensure the safe, long-term storage of CO₂ in this area, an extensive study was needed to select suitable geological formations and determine the storage capacity of each identified target. The research described here aimed to identify such geological targets and estimate the CO₂ storage capacity of North Carolina’s outer continental shelf

Yes / The process of capturing and storing carbon dioxide (CCS) was previously considered a crucial and time-sensitive approach for diminishing CO2 emissions originating from coal, oil, and gas sectors. Its implementation was seen necessary to address the detrimental effects of CO2 on the atmosphere and the ecosystem. This recognition was achieved by previous substantial study efforts. The carbon capture and storage (CCS) cycle concludes with the final stage of CO2 storage. This stage involves primarily the adsorption of CO2 in the ocean and the injection of CO2 into subsurface reservoir formations. Additionally, the process of CO2 reactivity with minerals in the reservoir formations leads to the formation of limestone through injectivities. Carbon capture and storage (CCS) is the final phase in the CCS cycle, mostly achieved by the use of marine and underground geological sequestration methods, along with mineral carbonation techniques. The introduction of supercritical CO2 into geological formations has the potential to alter the prevailing physical and chemical characteristics of the subsurface environment. This process can lead to modifications in the pore fluid pressure, temperature conditions, chemical reactivity, and stress distribution within the reservoir rock. The objective of this study is to enhance our existing understanding of CO2 injection and storage systems, with a specific focus on CO2 storage techniques and the associated issues faced during their implementation. Additionally, this research examines strategies for mitigating important uncertainties in carbon capture and storage (CCS) practises. Carbon capture and storage (CCS) facilities can be considered as integrated systems. However, in scientific research, these storage systems are often divided based on the physical and spatial scales relevant to the investigations. Utilising the chosen system as a boundary condition is a highly effective method for segregating the physics in a diverse range of physical applications. Regrettably, the used separation technique fails to effectively depict the behaviour of the broader significant system in the context of water and gas movement within porous media. The limited efficacy of the technique in capturing the behaviour of the broader relevant system can be attributed to the intricate nature of geological subsurface systems. As a result, various carbon capture and storage (CCS) technologies have emerged, each with distinct applications, associated prices, and social and environmental implications. The results of this study have the potential to enhance comprehension regarding the selection of an appropriate carbon capture and storage (CCS) application method. Moreover, these findings can contribute to the optimisation of greenhouse gas emissions and their associated environmental consequences. By promoting process sustainability, this research can address critical challenges related to global climate change, which are currently of utmost importance to humanity. Despite the significant advancements in this technology over the past decade, various concerns and ambiguities have been highlighted. Considerable emphasis was placed on the fundamental discoveries made in practical programmes related to the storage of CO2 thus far. The study has provided evidence that despite the extensive research and implementation of several CCS technologies thus far, the process of selecting an appropriate and widely accepted CCS technology remains challenging due to considerations related to its technological feasibility, economic viability, and societal and environmental acceptance.

Yes / Capturing and storing CO2 (CCS) was once regarded as a significant, urgent, and necessary option for reducing the emissions of CO2 from coal and oil and gas industries and mitigating the serious impacts of CO2 on the atmosphere and the environment. This recognition came about as a result of extensive research conducted in the past. The CCS cycle comes to a close with the last phase of CO2 storage, which is accomplished primarily by the adsorption of CO2 in the ocean and injection of CO2 subsurface reservoir formation, in addition to the formation of limestone via the process of CO2 reactivity with reservoir formation minerals through injectivities. CCS is the last stage in the carbon capture and storage (CCS) cycle and is accomplished chiefly via oceanic and subterranean geological sequestration, as well as mineral carbonation. The injection of supercritical CO2 into geological formations disrupts the sub-surface’s existing physical and chemical conditions; changes can occur in the pore fluid pressure, temperature state, chemical reactivity, and stress distribution of the reservoir rock. This paper aims at advancing our current knowledge in CO2 injection and storage systems, particularly CO2 storage methods and the challenges encountered during the implementation of each method and analyses on how key uncertainties in CCS can be reduced. CCS sites are essentially unified systems; yet, given the scientific context, these storage systems are typically split during scientific investigations based on the physics and spatial scales involved. Separating the physics by using the chosen system as a boundary condition is a strategy that works effectively for a wide variety of physical applications. Unfortunately, the separation technique does not accurately capture the behaviour of the larger important system in the case of water and gas flow in porous media. This is due to the complexity of geological subsurface systems, which prevents the approach from being able to effectively capture the behaviour of the larger relevant system. This consequently gives rise to different CCS technology with different applications, costs and social and environmental impacts. The findings of this study can help improve the ability to select a suitable CCS application method and can further improve the efficiency of greenhouse gas emissions and their environmental impact, promoting the process sustainability and helping to tackle some of the most important issues that human being is currently accounting global climate change. Though this technology has already had large-scale development for the last decade, some issues and uncertainties are identified. Special attention was focused on the basic findings achieved in CO2 storage operational projects to date. The study has demonstrated that though a number of CCS technologies have been researched and implemented to date, choosing a suitable and acceptable CCS technology is still daunting in terms of its technological application, cost effectiveness and socio-environmental acceptance.

La sorption de CO2 et de CH4 dans des charbons a été caractérisée au laboratoire afin d'étudier la faisabilité du stockage géologique de CO2 dans les veines de charbon. La diffusion et la sorption de CO2 et de CH4 sur des charbons du bassin de Lorraine et du bassin de Gardanne ont été étudiées par une méthode gravimétrique jusqu'à une pression de 5 MPa et pour des températures variant de 283 à 333 K. La cinétique de sorption dépend du gaz utilisé, de la granulométrie, de la pression en gaz et de la température. Elle peut être représentée par un modèle unipore basé sur la loi de Fick. Le coefficient de diffusion de CO2 dans le charbon est supérieur à celui du CH4 et est d'environ 10–12 m2 s–1, valeur de diffusion assez faible. A l'équilibre, la température, la pression, le gaz utilisé, la composition des charbons et la teneur en eau sont des paramètres qui influencent la capacité de sorption sur les charbons. Le charbon du bassin de Lorraine possède une plus grande capacité de sorption de CO2 (1,6 mmol g–1, soit ~ 36 m3 t–1) que celle du charbon du bassin de Gardanne. Le modèle de Dubinin-Astakhov basé sur un remplissage volumique des pores, rend mieux compte de la sorption de CO2 et CH4 que les modèles de Dubinin-Radushkevich et de Langmuir. Par ailleurs, les mécanismes de sorption de l'eau sur le charbon ont été mis en évidence, permettant de mieux interpréter l'influence de l'eau sur la capacité de sorption des gaz. A partir de l'ensemble des résultats, une évaluation des possibilités de stockage est discutée. Il en ressort la nécessité d'études complémentaires dans le but d'améliorer la perméabilité de la veine à l'échelle du site de stockage pour permettre une meilleure injectivité du gaz / The CO2 and CH4 sorption onto coals has been characterized in laboratory in order to study the feasibility of CO2 geological storage in coal seams. The diffusion and sorption of CO2 and CH4 on coals of Lorraine and Gardanne basins have been performed from a gravimetric method until a pressure of 5 MPa and for temperatures from 283 to 333 K. The kinetics of sorption depends on the nature of gas, the grain size of coal, the gas pressure and the temperature. It can be represented by a unipore model based on Fick's law. The CO2 diffusion coefficient on coal is higher than that of CH4 and is about 10–12 m2 s–1. At equilibrium, the temperature, pressure, nature of gas, composition of coal and water content are parameters that influence the sorption capacity of coals. The coal of Lorraine basin has a greater capacity for sorption of CO2 (1.6 mmol g–1, ~ 36 m3 t–1) than that of coal of Gardanne basin. The model of Dubinin-Astakhov based on a pore volume filling, has a best fit of sorption data that Dubinin-Radushkevich and Langmuir models. Finally, the different mechanisms of water sorption on coal have been identified and can better interpret the influence of moisture on the gas sorption capacity. From all results, an assessment of capacity storage is discussed. This indicates the need for further studies in order to improve the permeability of the coal seams across the storage site for better gas injectivity

TOTAL a choisi la voie du stockage géologique de CO2 en Béarn pour les fumées issues du pilote d’oxycombustion qui sont injectées dans un réservoir déplété de gaz naturel. Cependant, la mise en œuvre de cette technologie nécessite une connaissance des processus physiques, physico-chimiques et des interactions entre les phases depuis le captage jusqu’au stockage, d’autant plus que le CO2 injecté n’est pas pur. Il peut contenir par exemple quelques pourcents d’oxygène. Nous étudions plus précisément l’impact de l’injection d’un mélange de gaz (CO2 + O2) sur les roches de réservoir et de couverture en présence de saumure. A cette fin, un pilote expérimental a été développé et instrumenté pour acquérir des données thermodynamiques (solubilités et masses volumiques) et cinétiques de dégradation des roches indispensables aux modélisations et simulations thermodynamiques et réactives du système triphasique (gaz-saumure-roches) dans les conditions de stockage (T < 150°C et P < 200 bar). / TOTAL has chosen the path of geological storage of CO2 in Béarn flue gases from driver oxycombustion which are injected into a depleted natural gas reservoir. However, the implementation of this technology requires knowledge of physical processes and physico-chemical interactions between the phases from capture to storage, especially as the injected CO2 flow is not pure. It may contain a few percent of oxygen. The impact of the injection of a gas mixture (CO2 + O2) on reservoir rock and in the presence of coverage of brine is studied. An experimental pilot was developed and instrumented to acquire thermodynamic data (solubility and density) and kinetics of degradation of solids essential for modeling and simulations of thermodynamic and reactive three-phase system (gas-brine-rock) in storage conditions (T <150°C and P <200 bar).

The demand for large scale storage of carbon dioxide (CO2) grows stronger as incentives to reduce greenhouse gas emissions are introduced. Geological storage sites such as depleted oil and gas reservoirs, unminable coal seams and deep saline water-saturated aquifers are a few of many possible geological storage sites. Geological formations offer large scale storage potential, hidden locations and are naturally occurring world wide. A disadvantage is the difficulty to investigate the properties of storage material over large areas. Reservoir simulation studies addressing issues of heterogeneous reservoirs are growing in number. There is still much to investigate however this study adds to the field by investigating the significance of the heterogeneity in hydraulic conductivity based on core sample data. The data was received from the main CO2 injection site Heletz, Israel in the European Union Seventh Framework Programme for research and technological development (EU FP7) project MUSTANG (CO2MUSTANG, 2011-03-13). By developing models using iTOUGH2/ECO2N, the aim of this study is to contribute to a better understanding of how the average permeability, variance in permeability and spatial correlation of the reservoir properties affect the distribution of CO2 within the deep saline aquifer target layer. In this study a stochastic simulation approach known as the Monte Carlo method is applied. Based on core sample data, geostatistical properties of the data are determined and utilized to create equally probable realizations where properties are described through a probability distribution described by a mean and variance as well as a constructed semivariogram. The results suggest that deep saline aquifers are less storage effective for higher values of average permeability, variance in permeability and spatial correlation. The results also indicate that the Heletz aquifer, with its highly heterogeneous characteristics, in some extreme cases can be just as storage effective as a deep saline aquifer ten times as permeable consisting of homogeneous sandstone. / Incitament för minskningar av växthusgaser har på senare tid ökat efterfrågan för storskalig lagring av koldioxid (CO2). Geologiska lagringsplatser som exploaterade olje- och gasreservoarer, svårutvunna kollager och djupt belägna salina akvifärer är exempel på potentiella lagringsplatser. Sådana geologiska formationer erbjuder storskalig lagring, dold förvaring och är naturligt förekommande världen över. Dock finns det stora svårigheter i att undersöka de materiella egenskaperna för hela lagringsområden. Simuleringsstudier som hantera frågor gällande reservoarers heterogenitet växer i antal. Det finns fortfarande mycket kvar att undersöka och denna studie bidrar till detta forskningsområde genom att undersöka betydelsen av heterogenitet i hydraulisk konduktivitet för spridningen av koldioxid med hjälp av uppmätt brunnsdata. Data erhölls från lagringsplatsen Heletz i Israel som är den huvudsakliga lagringplatsen i projektet MUSTANG är en del av den Europeiska Unionens sjunde ramprogram för forskning och teknisk utveckling (EU FP7), (CO2MUSTANG, 2011/3/13). Genom att utveckla modeller med hjälp av programvaran iTOUGH2/ECO2N är syftet med denna studie att bidra till en bättre förståelse för hur den genomsnittliga permeabilitet, varians i permeabilitet samt rumslig korrelation av reservoaregenskaper påverkar fördelningen av CO2 i den djupa saltvattenakvifären Heletz. Denna studie använde sig av stokastisk simulering genom att tillämpa Monte Carlo-metoden. Med hjälp av tidigare uppmätt brunnsdata kunde geostatistiska egenskaper bestämmas för att skapa ekvivalent sannolika realiseringar. De geostatistiska egenskaperna beskrevs med en sannolikhetsfördelning genom medelvärde och varians samt ett konstruerat semivariogram. Resultaten tyder på att djupa saltvattenakvifärer är mindre lagringseffektiva vid högre värden av genomsnittlig permeabilitet, varians i permeabilitet och rumslig horisontell korrelation. Resultaten visar även att Heletz akvifär, med dess mycket heterogena egenskaper, i extrema fall kan vara lika lagringsineffektiv som en djupt belägen saltvattenakvifär med tio gånger högre genomsnittlig permeabilitet.