The objective of this study is to synthesize the geological and hydrogeological characteristics of the main aquifers in the Paris Basin within the Cenozoic sedimentary formations. This work is part of the multi-annual scientific program RGF (Référentiel Géologique de la France, https://rgf.brgm.fr/page/bassin-parisien), which aims to update the representation and mapping of French geology on a national scale. The program also funds several PhD projects in collaboration with the academic community, focusing on the geometry, distribution of petrophysical properties, modeling, and mapping of key Cenozoic geological formations in the basin. Particular emphasis is placed on the major aquifers as part of this modeling effort.The geology of the Paris Basin has been extensively documented by various authors (Pomerol, 1967; Mégnien, 1980; Gély and Lorenz, 1991; Briais, 2015). Data from well logs and core descriptions collected from over 2,000 petroleum wells have been used to reconstruct the stratigraphic surfaces of the main formations, while also identifying the large-scale geometries of associated aquifers and aquitards. Recent studies have enhanced the dating of specific stratigraphic markers (Marlot, 2023; Moreau, 2023), described the geometries of alluvial formations in the Seine River (Chourio-Camacho, 2024), advanced knowledge in structural geology (Brown, 2024), and provided petrophysical characterizations of reservoir rocks (Moreau, 2023; Marie, 2024).The hydrogeology of the Paris Basin has been studied and modeled for decades (Mégnien, 1980; Goncalves, 2003; Lamé, 2013). The lateral extent of aquifers varies significantly across regions. For instance, in Île-de-France, the hydrosystem comprises six primary aquifers: the Alluvial, Brie, Champigny, Lutetian, Ypresian, and Chalk aquifers. However, lateral facies variations can significantly alter hydrogeological properties, influencing groundwater resource potential. In the Oligocene formations, the main aquifers are primarily located in Île-de-France and the northern part of the Centre-Val de Loire region: i) on the Beauce plateau, commonly referred to as the "Beauce aquifer," ii) in the Yvelines area, primarily associated with the Fontainebleau Sands, and iii) on the Brie and Bière plateaus, where they are predominantly contained within the Brie Limestone.These lateral facies variations, coupled with the presence of fractures or karstification, result in substantial differences in the petrophysical properties of the identified aquifers and aquitards. Pumping test data have been compiled and converted into permeability and transmissivity coefficients, which were subsequently mapped along lateral transects in the Brie region of the basin (Marie, 2024).This study will also contribute to the harmonization of the lithostratigraphic framework across the 187 geological maps covering the territory. Furthermore, the 3D model will facilitate vertical and lateral interpolation of hydrological reference data from the BDLISA database (https://bdlisa.eaufrance.fr/), which currently provides detailed mapping of water bodies at the scale of metropolitan France.

We present a panel of numerical modeling studies aimed to improve groundwater management resources for different contexts in the Northern part of France (the 'Hauts-de-France' Region). The objective is to demonstrate the capacities and limitations of modeling tools in reproducing observed data and providing predictions on the groundwater evolution under increasing anthropic pressures and climate change. Numerical models are developed in 3D at the regional scale to evaluate various scenarios of groundwater management, considering several types of anthropic or natural constraints such as pumping for irrigation, drinking water and/or industrial use, land use evolution, and modifications in precipitation and/or evapotranspiration due to climate change. In the three case studies presented, groundwater models are developed using BRGM’s 3D volume finite numerical tool MARTHE. The first case aims to characterize groundwater dynamics to identify the risks of flooding in the sewerage network of the urban communities of Lens-Liévin. The second case explores the role of land use in groundwater modeling for the sustainable management of the Lille Metropolitan Area. The third case evaluates the impact of climate change on the groundwater resource of the Somme River watershed. Limitations and capacities to assess such complex hydrogeological systems are discussed, particularly concerning the uncertainty in the simulated results, the CPU time and space resolution constraints necessary for a meaningful calibration of observed data.

In a reservoir characterization study of the Hontomín deep saline aquifer, the impact of geological heterogeneities on reservoir storage capacity and the migration of the CO2 plume is explored. This work presents, for the first time, very long-term (up to 200 years) simulations of CO2 injection into the naturally fractured Sopeña Formation, of the lower Jurassic age, at Hontomín. CO2 injection was simulated as a dual permeability case with Eclipse compositional software. The matrix permeability of the carbonate reservoir is quite low (0.5 mD) and thus fluid flow through the fractures dominates. The reservoir is dissected by eight normal faults which limited its south-east extension and divided it into several segments. The effect of geological heterogeneities was tested through scenario-based modeling and variation of parameters characterizing heterogeneity within realistic limits based on other similar formations. This modeling approach worked well in Hontomín where the database is completely scarce. The plume migration, the reservoir storage capacity, and pressure, were each influenced in diverse ways by incorporating particular types of heterogeneities. The effect of matrix heterogeneities on reservoir storage capacity was substantial (by factors up to ∼2.8×), compared to the plume migration. As the reservoir matrix permeability heterogeneity increased, the reservoir storage capacity markedly decreased, whilst an increase in porosity heterogeneity significantly increased it. The vertical gas migration in the homogeneous base case was relatively larger compared to the heterogeneous cases, and gas accumulated underneath the caprock via hydrodynamic trapping. It was also observed that, in heterogeneous cases, gas saturation in rock layers from top to bottom was relatively high compared to the base case, for which most of the gas was stored in the topmost layer. In contrast, the impact on storage capacity and plume movement of matrix vertical to horizontal permeability ratio in the fractured carbonate reservoir was small. The impact of the transmissibility of faults on reservoir pressure was only observed when the CO2 plume reached their vicinity.

The RGF-BP is the Paris Basin work programme of the French Geological Reference Platform (see Calcagno et al., same session) designed by the BRGM as a national programme for the acquisition and management of geological data. In the continuation of the 1:50000 scale geological maps, covering the whole country, the RGF-BP intends to improve the knowledge of the Paris Basin geology with specific focuses on: (i) the Grand Paris field work conducted for the development of new underground transport lines (metro and RER), (ii) the Tertiary and Quaternary sedimentary formations with the resolution of the geological maps and (iii) the deeper formations from Cretaceous to the Trias which reaches the crystalline basement formations. The main objectives of the RGF-BP are to obtain harmonized numerical geological maps of the Paris Basin, correlated 3D geometries of the sedimentary formations and 3D models populated with geotechnical, hydrogeological, geothermal and geochemical properties, all freely accessible to the public. This large piece of work involved the collection of existing and new data to be validated and incorporated into a common numerical referential (common lithological referential, update of geological maps, correlation transect, datation horizon) validated by the data providers, industries and the scientific community involved in the project via pHD ad Masters. The new knowledge on subsoils developed by the RGF-BP intends to support innovative responses to a wide range of issues facing our society, e.g. surface and subsurface planning, water and mineral resources management, energy prospection and storage, and risk mitigation.

We propose an approach for estimating the permeability tensor using seismic emission induced by borehole hydraulic tests or by a fluid injection of an arbitrary nature. This approach provides a single estimation of the permeability tensor for the complete heterogeneous rock volume, where the seismic emission was recorded. The approach is an extension of the method proposed by Shapiro et al, (1997) for isotropic case. It is based on the hypothesis, that the triggering front of the hydraulic-induced microseismicity propagates like the low-frequency second-type compressional Biot wave (corresponding to the process of the pore-pressure relaxation) in an effective homogeneous anisotropic poroelastic fluid-saturated medium. The permeability tensor of this effective medium is the permeability tensor of the heterogeneous rock volume upscaled to the characteristic size of the seismic-active region. We demonstrate the method using the microseismic data collected during the Hot-Dry-Rock Soultz-sous-Forˆ ets experiment (Dyer et al., 1994). These data show that the corresponding rock volume is characterized by a significant permeability anisotropy caused by oriented crack systems. The maximal principal component of the permeability tensor has a subvertical orientation. It is about seven times larger than the minimal subhorizontal principal component.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Predicting long-term geochemical alteration of wellbore cement in a generic geological CO2 confinement site: tackling a difficult reactive transport modeling challenge Fabrizio Gherardi, Pascal Audigane, Eric C. Gaucher

To provide quantitative data for the development of underground hydrogen storage in porous sedimentary rocks, capillary pressures and relative permeabilities have been measured for the hydrogen–water system. The tests have been performed on a Triassic sandstone. Two potential underground hydrogen storage conditions (“shallower”: 55 bar, 20 \(^{\circ }\hbox {C}\) and “deeper”: 100 bar, 45 \(^{\circ }\hbox {C}\)) have been investigated. Capillary pressure curves have been measured following a modified semi-dynamic technique. The data have been combined with mercury injection capillary pressure measurements to derive a model for capillary pressure valid over almost the entire water saturation range. Interfacial tensions and contact angles for the hydrogen–water system have been also derived. Relative permeability curves measured with the steady-state technique yield low values for minimum water saturations of \(\sim \) 40%. When combined with the capillary pressure data, the relative permeability of hydrogen in sandstone can be evaluated for almost the total range of water saturation. Capillary numbers calculated for our relative permeability experiments indicate a capillary-limited flow regime for the hydrogen–water system. Despite the two differing sets of conditions investigated and this flow regime, the relative permeability curves stay very close from each other, an effect attributed to the almost constant viscosity of hydrogen under our pressure and temperature conditions. This is in contrast with other fluid pairs (e.g., \(\hbox {CO}_{2}\)–water system) where capillary numbers can strongly vary with pressure and temperature. Similarly, capillary pressure data vary little between the experimental conditions. The interpretation of the results would suggest that the relative permeability and capillary pressure results from this study are applicable to a wide range of pressure and temperature conditions.

The use of hydrogen as an alternative for electric energy storage has emerged recently. Being composed of small molecules, hydrogen has a strong ability to migrate in porous medium and can also be highly reactive with rock-forming minerals. In the case of storage in sedimentary rocks such as sandstone, mineralogical transformations due to the presence of hydrogen may modify the porous structure of the rock and affect the storage properties. In this study, the geochemical reactivity of hydrogen with sandstone was assessed both experimentally and numerically. Experiments were performed to test the possibility of mineral transformations due to hydrogen, either pure or in presence of water. The experiments were carried out mostly at 100 and more rarely at 200 degrees C. Maximum hydrogen pressures of 100 bar were imposed and experimental durations ranged from 1.5 to 6 months. The experimental products bear the mark of only very limited reaction between minerals in sandstone and hydrogen. Taken together with the numerical results, this study demonstrates that hydrogen, once injected, can be considered as relatively inert. Overall, our results support the feasibility of hydrogen confinement in geological reservoirs such as sandstones.

Abstract This paper recall the Compositional Dual Mesh Method, an extension to the concept of dual mesh for reactive transport modeling. This approach involves two meshes, a low-resolution mesh to resolve the pressure equation and a high-resolution mesh to transport the species and to calculate the geochemical equilibrium. Geochemical equilibrium being very sensitive to the concentration, preserving the fine heterogeneities leads to a more accurate field behavior simulation than conventional approach which consist in performing simulations on a coarser mesh. The method is applied to a simulation of CO2 storage in a geological model representing a fluvial deposit with a complex realistic architecture that keep a high resolution of the heterogeneities.

In the present study, we assess the potential for initiating ductile failure in a fractured caprock due to the chemical alteration of its mechanical properties under pressure increase induced by CO 2 leakage and fixed in situ boundary conditions. In this view, 2D numerically coupled reactive-transport simulations were set up by using the Opalinus Clay formation as an analogue for a caprock layer. The fractured system was viewed as a compartmentalised system that consists of a main highly permeable pathway, a moderately permeable damage zone and the intact rock. The outputs of the numerical simulations (mineral fraction, porosity changes, gas saturation, pore-fluid pressure) were converted into parameter changes of the yield surface by viewing the rock material of the three compartments (fault, damage zone and intact rock) as a composite system that consists of a clayey solid material, pores and mineral inclusions (such as carbonate and quartz). Three alteration processes were considered: (1) the effect of the mineral fraction and porosity evolution on the yield surface, (2) changes in the resulting poro-elastic properties and (3) the suction effect, i.e. the bounding effect induced by the presence of two phases, water and CO 2 . Our numerical investigations showed that the decrease in the friction coefficient remained negligible during leakage, while the pre-consolidation stress mainly decreased. Consequently, the damage zone of the fractured system became more collapsible over time, which was driven by low-to-moderate pressure build-up of the fluid penetrating the fault (1 MPa in our case). For the considered case, the initiation of ductile failure is likely under conditions of fixed vertical stress and zero lateral strain. This process could potentially limit the spatial spreading of CO 2 -induced alteration, although this remains very site specific. We recommend that characterisation efforts be intensified to obtain better insight into the properties of fracture systems in caprock-like formations (with special attention to their initial over consolidation ratio).

To meet the ambitious EC target of an 80% reduction in greenhouse gas emissions by 2050, CO2 Capture and Storage (CCS) needs to move rapidly towards full scale implementation with geological storage solutions both on and offshore. Onshore storage offers increased flexibility and reduced infrastructure and monitoring costs. Enabling onshore storage will support management of decarbonisation strategies at territory level while enhancing security of energy supply and local economic activities, and securing jobs across Europe. However, successful onshore storage also requires overcoming some unique technical and societal challenges. ENOS will provide crucial advances to help foster onshore CO2 storage across Europe through: 1. Developing, testing and demonstrating in the field, under "real-life conditions", key technologies specifically adapted to onshore storage. 2. Contributing to the creation of a favourable environment for onshore storage across Europe. The ENOS site portfolio will provide a great opportunity for demonstration of technologies for safe and environmentally sound storage at relevant scale. Best practices will be developed using experience gained from the field experiments with the participation of local stakeholders and the lay public. This will produce improved integrated research outcomes and increase stakeholder understanding and confidence in CO2 storage. In this improved framework, ENOS will catalyse new onshore pilot and demonstration projects in new locations and geological settings across Europe, taking into account the site-specific and local socio-economic context. By developing technologies from TRL4/5 to TRL6 across the storage lifecycle, feeding the resultant knowledge and experience into training and education and cooperating at the pan-European and global level, ENOS will have a decisive impact on innovation and build the confidence needed for enabling onshore CO2 storage in Europe. ENOS is initiating strong international collaboration between European researchers and their counterparts from the USA, Canada, South Korea, Australia and South Africa for sharing experience worldwide based on real-life onshore pilots and field experiments. Fostering experience-sharing and research alignment between existing sites is key to maximise the investment made at individual sites and to support the efficient large scale deployment of CCS. ENOS is striving to promote collaboration between sites in the world through a programme of site twinning, focus groups centered around operative issues and the creation of a leakage simulation alliance. (c) 2017 The Authors. Published by Elsevier Ltd.

To prevent the release of large quantities of CO2 into the atmosphere, carbon capture and storage (CCS) represents a potential means of mitigating the contribution of fossil fuel emissions to global warming and ocean acidification. Fluvial saline aquifers are favourite targeted reservoirs for CO2 storage. These reservoirs are very heterogeneous but their heterogeneities were rarely integrated into CO2 reservoir models. Moreover, contrary to petroleum reservoirs, the available dataset is very limited and not supposed to be enriched. This leads to wide uncertainties on reservoir characteristics required for CSS management (injection location, CO2 plume migration, etc.). Stochastic simulations are classical strategies in such under-constrained context. They aim at generating a wide number of models that all fit the available dataset. The generated models serve as support for computing the required reservoir characteristics and their uncertainties. A challenge is to optimize the uncertainty computations by selecting stochastic models that should have a priori very different flow behaviours. Fluid flows depend on the connectivity of reservoir rocks (channel deposits). In this paper, it is proposed to study the variability of the Betti numbers in function of different fluvial architectures. The aim is to quantify the impact of fluvial heterogeneities and their spatial distribution on reservoir rock topology and then on CO2 storage capacities. Representative models of different scenarios of channel stacking and their internal heterogeneities are generated using geostatistical simulation approaches. The Betti numbers are computed on each generated models and statistically analysed to exhibit if fluvial architecture controls reservoir topology.

In this sensitivity analysis on a 3D model of a heterogeneous fluvial reservoir, two scenario orders have been considered. The first one focuses on the first-order heterogeneity (i.e. a fluvial belt with a 100% sand content), and the other one on the second-order heterogeneity accounting for the internal sedimentary fill within the fluvial belt (oxbow lakes). CO2 injections were simulated using THOUGH2, and the dynamic simulations show large variations of reservoir performances. The first-order heterogeneity generates a large spectrum of storage capacities ranging from 30 to 50 Mt, to be related to the natural connectivity variability between fluvial belts induced by the avulsion process. Considering second-order heterogeneity reduces the storage capacities by 30%, highlighting the importance of representing such objects in complex heterogeneous systems. Moreover, it increases the dissolution process, increasing by the way the storage efficiency. The CO2 plume extension and geometry is also estimated to be strongly dependent on the level of heterogeneity. Finally, trapping into poorly connected fluvial point bars affects strongly the storage capacity of the mobile CO2 as well as the pressure field.