Modélisation thermochimique et poroélastique de la cristallisation de sel, et nouveau dispositif expérimental d’écoulement multiphasique : comment prédire l’évolution de l’injectivité pour le stockage du CO2 en aquifère profond ?

In a context of international reduction of greenhouse gases emissions, CCS (ce{CO2} Capture and Storage) appears as a particularly interesting midterm solution. Indeed, geological storage capacities may raise to several millions of tons of ce{CO2} injected per year, allowing to reduce substantially the atmospheric emissions of this gas. One of the most interesting targets for the development of this solution are the deep saline aquifers. These aquifers are geological formations containing brine whose salinity is often higher than sea water's, making it unsuitable for human consumption. However, this solution has to cope with numerous technical issues, and in particular, the precipitation of salt initially dissolved in the aquifer brine. Consequences of this precipitation are multiple, but the most important is the modification of the injectivity i.e. the injection capacity. Knowledge of the influence of the precipitation on the injectivity is particularly important for both the storage efficiency and the storage security and durability. The aim of this PhD work is to compare the relative importance of negative (clogging) and positive (fracturing) phenomena following ce{CO2} injection and salt precipitation. Because of the numerous simulations and modelling results in the literature describing the clogging of the porosity, it has been decided to focus on the mechanical effects of the salt crystallization and the possible deformation of the host rock. A macroscopic and microscopic modelling has then been developed, taking into account two possible modes of evaporation induced by the spatial distribution of residual water, in order to predict the behavior of a porous material subjected to the drying by carbon dioxide injection. Results show that crystallization pressure created by the growth of a crystal in a confined medium can reach values susceptible to locally exceed the mechanic resistance of the host rock, highlighting the importance of these phenomena in the global mechanical behavior of the aquifer. At the experimental level, the study of a rock core submitted to the injection of supercritical carbon dioxide has been proceeded on a new reactive percolation prototype in order to obtain the evolution of permeabilities in conditions similar to these of a deep saline aquiferDans un contexte de réduction internationale des émissions de gaz à effet de serre, les techniques de Captage Transport et Stockage de ce{CO2} (CTSC) apparaissent comme une solution à moyen terme particulièrement efficace. En effet, les capacités de stockage géologique pourraient s'élever jusqu'à plusieurs millions de tonnes de ce{CO2} injectées par an, soit une réduction substantielle des émissions atmosphériques de ce gaz. Une des cibles privilégiées pour la mise en place de cette solution sont les aquifères salins profonds. Ces aquifères sont des formations géologiques contenant une saumure dont la salinité est souvent supérieure à celle de la mer la rendant impropre à la consommation. Cependant, cette technique fait face à de nombreux défis technologiques; en particulier la précipitation des sels, dissous dans l'eau présente initialement dans l'aquifère cible, suite à son évaporation par le ce{CO2} injecté. Les conséquences de cette précipitation sont multiples, mais la plus importante est une modification de l'injectivité, c'est-à-dire des capacités d'injection. La connaissance de l'influence de la précipitation sur l'injectivité est particulièrement importante tant au niveau de l'efficacité du stockage et de l'injection qu'au niveau de la sécurité et de la durabilité du stockage. Le but de ces travaux de thèse est de comparer l'importance relative des phénomènes négatif (colmatage) et positif (fracturation) consécutifs à l'injection de ce{CO2} et à la précipitation des sels. Au vu des nombreux résultats de simulations et de modélisation dans la littérature décrivant le colmatage de la porosité, il a été décidé de porter l'accent sur les effets mécaniques de la cristallisation des sels et la possible déformation de la roche mère. Une modélisation macroscopique et microscopique, tenant compte de deux modes possibles d'évaporation induits par la distribution spatiale de l'eau résiduelle a donc été développée afin de prédire le comportement mécanique d'un matériau poreux soumis à un assèchement par injection de ce{CO2}. Les résultats montrent que la pression de cristallisation consécutive à la croissance d'un cristal en milieu confiné peut atteindre des valeurs susceptibles localement de dépasser la résistance mécanique du matériau, soulignant ainsi l'importance de ces phénomènes dans le comportement mécanique global de l'aquifère. Sur le plan expérimental, les travaux ont porté sur l'utilisation d'un nouveau prototype de percolation réactive afin de reproduire le comportement d'une carotte de roche soumise à l'injection et ainsi obtenir l'évolution des perméabilités dans des conditions similaires à celle d'un aquifèr

Experimental study of the co-valorization of carbon dioxide storage through hydrogen production in ultramafic geological formations

International audienceWith the recent IPCC report about global warming urging humanity to limit the global temperature increase to 2°C maximum, research on the geological storage of carbon dioxide appears more important than ever. However, the injection in geological formations (such as deep saline aquifers and depleted gas/oil fields) of supercritical CO2, stores it in the porosity of the host rock raising legitimate concern about the safety and long-term behavior of such dynamic multiphase hydrosystems. Additionally, the economic and energetic weight of such storage complicates its development at the world scale without strong political incentives. The storage of CO2 in ultramafic formations in some specific contexts appears, on the contrary, as a very appealing technology since it involves the safe mineralization of the carbon by precipitation of carbonates with the major alkaline earth metals (i.e. Mg, Ca…) leached from the formation itself. Moreover, as these rocks contain high amounts of ferrous iron, its oxidation by the water co-injected with CO2 produces dihydrogen, which can be economically valuable rendering the whole process more viable. Large ophiolite formations (Oman, Papua New Guinea, east coast of Adriatic Sea…) are expected to have a storage capacity of several billion tons of CO2 and could produce similar amounts of clean dihydrogen. We present experimental results on the mineral carbonation of natural cores of serpentinites by the continuous percolation of carbon-saturated water. We show that the dimensionless Péclet (relative importance of diffusion and convection processes), and Damköhler (relative importance of convection and chemical processes) numbers as well as the initial geometry of the porosity and permeability control the localization of the silicate dissolution and the carbonate precipitation in the porous medium. We also show that the chemical behavior is principally controlled by the reactivity of calcium-bearing silicates (wollastonite, diopside) and the precipitation of calcite as well as the initial iron content of the different phases. Such results are particularly interesting for the design and the optimization of pilot sites and the development of this technology at industrial scale

Experimental study of the co-valorization of carbon dioxide storage through hydrogen production in ultramafic geological formations

International audienceWith the recent IPCC report about global warming urging humanity to limit the global temperature increase to 2°C maximum, research on the geological storage of carbon dioxide appears more important than ever. However, the injection in geological formations (such as deep saline aquifers and depleted gas/oil fields) of supercritical CO2, stores it in the porosity of the host rock raising legitimate concern about the safety and long-term behavior of such dynamic multiphase hydrosystems. Additionally, the economic and energetic weight of such storage complicates its development at the world scale without strong political incentives. The storage of CO2 in ultramafic formations in some specific contexts appears, on the contrary, as a very appealing technology since it involves the safe mineralization of the carbon by precipitation of carbonates with the major alkaline earth metals (i.e. Mg, Ca…) leached from the formation itself. Moreover, as these rocks contain high amounts of ferrous iron, its oxidation by the water co-injected with CO2 produces dihydrogen, which can be economically valuable rendering the whole process more viable. Large ophiolite formations (Oman, Papua New Guinea, east coast of Adriatic Sea…) are expected to have a storage capacity of several billion tons of CO2 and could produce similar amounts of clean dihydrogen. We present experimental results on the mineral carbonation of natural cores of serpentinites by the continuous percolation of carbon-saturated water. We show that the dimensionless Péclet (relative importance of diffusion and convection processes), and Damköhler (relative importance of convection and chemical processes) numbers as well as the initial geometry of the porosity and permeability control the localization of the silicate dissolution and the carbonate precipitation in the porous medium. We also show that the chemical behavior is principally controlled by the reactivity of calcium-bearing silicates (wollastonite, diopside) and the precipitation of calcite as well as the initial iron content of the different phases. Such results are particularly interesting for the design and the optimization of pilot sites and the development of this technology at industrial scale

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

Reactive percolation experiments of the co-valorization of carbon dioxide geological storage through hydrogen production in ultramafic formations.

International audienceThe discovery of deep ocean smokers revealed the importance of hydrogen in the global mass balance between the upper mantle, the oceanic crust and the ocean, as well as its fundamental role in the deep ocean biosphere. Nowadays, hydrogen is also highly regarded as a potential replacement for fossil fuel in a growing number of applications. In parallel, the development of geological carbon dioxide storage technologies highlighted the potential of ultramafic formations as a recipient for CO2 mineralization due to their high reactivity (peridotite+CO2 = carbonates+silica), offering huge storage capacities, 10 to 100 times larger than the required amount for climate stabilization, and with no risk of leakage back to the surface. The combination of these two phenomena appears then as a natural development, allowing the offset of the carbonation costs in ultramafic formations by the production of clean and natural hydrogen fueling the energy transition, in a process where CO2-rich brine is injected in the formation and an H2-rich fluid is extracted from the other side In this study, we present several reactive percolation experiments in natural serpentinite cores from the South-West Indian Oceanic Ridge, with fluids either NaCl-only or NaClNaHCO3 brine. The purpose was to analyze the influence of parameters such as temperature, pressure, inlet solution composition on the hydrogen production as well as the CO2 storage efficiency. Results show that the carbonation leads to a fast and complete clogging of the cores by the precipitation of carbonates in the main percolation paths. On the contrary, NaCl-brine experiments presented a steady but much slower decrease in permeability. However, despite the fast clogging, carbonation extent reached interesting levels, e.g. 31% efficiency at 280°C and 200 bars. On the other hand, hydrogen production presents lower levels in the CO2 experiments than in the CO2-free experiments, highlighting competition between iron oxidation and its incorporation in the secondary phases. These results will not only help understand the complicated coupling between hydrogen formation and CO2 storage in a potential industrial development of the technology, but also help describe the interplay of serpentinization and carbonation in natural settings such as mid-oceanic ridges or subduction zones

Microfluidic measurement of the dissolution rate of gypsum in water using the reactive infiltration-instability

We present an original method for measuring the intrinsic dissolution rate of gypsum. We use a simple microfluidic setup, with a gypsum block inserted between two polycarbonate plates, which is dissolved by water. By changing the flow rate and the distance between the plates, we can scan a wide range of Péclet and Damköhler numbers, characterizing the relative magnitude of advection, diffusion and reaction in the system. We find the dissolution to be unstable, with a formation of a characteristic fingering pattern. The dissolution rate can then be calculated from the initial wavelength of this pattern. Alternatively, it can also be estimated from the time it takes for the gypsum chip to get completely dissolved near the inlet channel. The method presented here is general and can be used to assess the dissolution rates of other minerals

Recommendations for integrating isotope fingerprinting in Environmental Baseline Assessment as part of regulation on unconventional gas exploration and exploitation

International audienceMulti-isotope fingerprinting of gases (methane, higher alkanes, CO 2) and of dissolved compounds in saline fluids (C, S, O, Sr, B, Li, U, Cu, Zn,…) allows for the discrimination of point contamination related to unconventional gas development compared to the environmental baseline. We present results from a multitude of settings worldwide with a focus on the identification of thermogenic stray gases from the natural background values, taking into account the prevailing redox conditions. A second aspect are the specific isotope fingerprints of flowback waters from hydraulic fracturing compared to natural saline fluids

A Probabilistic Approach for Predicting Methane Occurrence in Groundwater

Aqueous geochemistry datasets from regional groundwater monitoring programs can be a major asset for environmental baseline assessment (EBA) in regions with development of natural gases from unconventional hydrocarbon resources. However, they usually do not include crucial parameters for EBA in areas of shale gas development such as methane concentrations. A logistic regression (LR) model was developed to predict the probability of methane occurrence in aquifers in Alberta (Canada). The model was calibrated and tested using geochemistry data including methane concentrations from two groundwater monitoring programs. The LR model correctly predicts methane occurrence in 89.8% (n = 234 samples) and 88.1% (n = 532 samples) of groundwater samples from each monitoring program. Methane concentrations strongly depend on the occurrence of electron donors such as sulfate and to a lesser extent on well depth and the total dissolved solids of groundwater. The model was then applied to a province-wide public health groundwater monitoring program (n = 52,849 samples) providing aqueous geochemistry data but no methane concentrations. This approach allowed the prediction of methane occurrence in regions where no groundwater gas data are available, thereby increasing the resolution of EBA in areas of shale gas development by using basic hydrochemical parameters measured in high-density groundwater monitoring programs

Solubility of NaCl under anisotropic stress state

Salt solubility is generally determined under isotropic stress conditions. Yet, in the context of salt weathering of porous media, mechanical constraints on the in-pore growth of salt crystals are likely to be orientation-dependent, resulting in an anisotropic stress state on the crystal. In this paper, we determine by molecular simulation the solubility of NaCl in water when the crystal is subjected to anisotropic stress. Such anisotropy causes the chemical potential of the crystal to be orientation-dependent, and proper thermodynamic formulation requires describing the chemical potential as a tensor. The solute and crystal chemical potentials are computed from free energy calculations using Hamiltonian thermodynamic integration, and the usual condition of solubility is reformulated to account for the tensorial nature of the crystal chemical potential. We investigate in detail how the uniaxial compression of the crystal affects its solubility. The molecular simulation results led to revisiting the Correns law under anisotropic stress. Regarding the solute, the non-ideal behavior of the liquid phase is captured using Pitzer’s ion interaction approach up to high concentrations of interest for in-pore crystallization and beyond the concentrations addressed in the existing literature. Regarding NaCl crystals, the validity of the generalized Gibbs–Duhem equation for a tensorial chemical potential is carefully verified, and it is found that crystallization progresses almost orthogonally to the crystal surface even under high shear stresses. Comparing uniaxial and isotropic compression highlights the major differences in solubility caused by stress anisotropy, and the revisited Correns law offers an appropriate framework to capture this phenomenon

Time-dependent shapes of a dissolving mineral grain: Comparisons of simulations with microfluidic experiments

International audienceExperimental observations of the dissolution of calcium sulfate by flowing water have been used to investigate the assumptions underlying pore-scale models of reactive transport. Microfluidic experiments were designed to observe changes in size and shape as cylindrical disks (radius 10 mm) of gypsum dissolved for periods of up to 40 days. The dissolution flux over the whole surface of the sample can be determined by observing the motion of the interface. However, in order to extract surface reaction rates, numerical simulations are required to account for diffusional hindrance across the concentration boundary layer; the geometry is too complex for analytic solutions.We have found that a first-principles simulation of pore-scale flow and transport, with a single value of the surface reaction rate, was able to reproduce the time sequence of sample shapes without any fitting parameters. The value of the rate constant is close to recent experimental measurements but much smaller than some earlier values. The shape evolution is a more stringent test of the validity of the method than average measurements such as effluent concentration, because it requires the correct flux at each point on the sample surface