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The two-phase flow characterization (CO 2 /water) of a Triassic sandstone core from the Paris Basin, France, is reported in this paper. Absolute properties (porosity and water permeability), capillary pressure, relative permeability with hysteresis between drainage and imbibition, and residual trapping capacities have been assessed at 9 MPa pore pressure and 28 C (CO 2 in liquid state) using a single core-flooding apparatus associated with magnetic resonance imaging. Different methodologies have been followed to obtain a data set of flow properties to be upscaled and used in large-scale CO 2 geological storage evolution modeling tools. The measurements are consistent with the properties of well-sorted water-wet porous systems. As the mineralogical investigations showed a nonnegligible proportion of carbonates in the core, the experimental protocol was designed to observe potential impacts on flow properties of mineralogical changes. The magnetic resonance scanning and mineralogical observations indicate mineral dissolution during the experimental campaign, and the core-flooding results show an increase in porosity and water absolute permeability. The changes in two-phase flow properties appear coherent with the pore structure modifications induced by the carbonates dissolution but the changes in relative permeability could also be explained by a potential increase of the water-wet character of the core. Further investigations on the impacts of mineral changes are required with other reactive formation rocks, especially carbonate-rich ones, because the implications can be significant both for the validity of laboratory measurements and for the outcomes of in situ operations modeling.

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International audienceThis article presents the main outputs from the multidisciplinary Carmex project (2009-2012), which was concerned with the possibility of applying ex situ mineral carbonation concepts to mafic/ultramafic mining wastes. Focus points of the project included (i) matching significant and accessible mining wastes to large CO2 emitters through a dedicated geographical information system (GIS), (ii) analysis of aqueous carbonation mechanisms of mining waste and process development and (iii) environmental assessment of ex situ mining waste carbonation through life cycle assessment (LCA) methodology. With a number of materials associated with the mining sector, the project took a close look at the aqueous carbonation mechanisms for these materials and obtained unexpected carbonation levels (up to 80%) by coupling mechanical exfoliation and reactive carbonation. Results from this work support the possibility of processing serpentine-rich peridotites without applying the classical first step of heat activation. Perspectives are also given for the carbonation of Ni-pyrometallurgical slag available closed to ultramafic mining residues. LCA of the mining waste carbonation system as a whole made it clear that the viability of this CO2 storage option lies with the carbonation process itself and optimisation of its operating conditions. By combining the body of knowledge acquired by this project, it is concluded that New Caledonia, with its insularity and local abundance of 'carbonable' rocks and industrial wastes coupled with significant greenhouse gas (GHG) emissions from world-class nickel pyro and hydrometallurgical industries stands out as a strong potential candidate for application of ex situ mineral carbonation

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[1] Chemical osmosis is considered a plausible cause of abnormal pressures in shale formations of sedimentary basins. A set of experimental data on chemical osmosis was recently obtained for different shales, mainly in the framework of studies on radioactive waste repositories in deep argillaceous formations. Based on these data, large, osmotically induced overpressures up to tens of MPa were predicted by Neuzil and Provost [2009] under appropriate conditions. However, such large overpressures have not been found in sedimentary basins such that the reasons for this disparity between predictions and observations need to be clarified. Accordingly, two natural causes for lower than expected osmotic pressure were investigated: the effect of the complex composition of natural waters, including both monovalent and divalent cations, on the osmotic efficiency and the resulting abnormal pressures, and the presence of steady state rather than transient-state salinity distributions. For this purpose, an electrical triple-layer model accounting for multi-ionic solutions was developed and used to calculate the osmotic efficiency at different proportions of monovalent and divalent cations. The calculated decrease of the osmotic efficiency when Ca 2þ is introduced in a Na þ -clay system yields a noticeable decrease in the ability of the shale to generate overpressures. A discussion addresses the generation of abnormal pressures at steady state conditions found in sedimentary basins, i.e., with a linear distribution of the concentration across the formation. The persistence of moderate overpressures was predicted because of the nonlinearity associated with the dependence of the chemo-osmotic efficiency on the concentration and the porosity. Finally, a case study of the moderate excess hydraulic head measured in the Toarcian/Domerian argillaceous formation of Tournemire (SE of France) was investigated. The analysis indicated an osmotic origin for the excess head and illustrated the influence of the pore water composition.

International audienceSaline aquifers are choice targets for geological storage of CO2because of their storage potential andbecause these formations are not suitable for other uses. Geochemical modeling is an interesting tool toassess the geochemical behavior of CO2in the saline aquifer, including its dissolution in the brine andits interactions with minerals. Two key parameters which determine the confidence one can have in theresults of geochemical modeling are tested in this paper: (i) the establishment of the conceptual model,including the selection of the primary and secondary minerals expected to react; and (ii) the activitymodel and the associated thermodynamic databases to calculate the interaction energies within thesaline solution. In this study, we performed an analysis of a large set of CO2storage natural analogs, whichmakes it possible to identify the minerals that are likely to precipitate and dissolve during CO2-brine-rockinteractions. Interestingly, this analysis indicates a strong dependence of Dawsonite precipitation on theinitial sandstone mineralogy. Dawsonite can precipitate in lithic and feldspar rich sandstones but wasnot observed in quartz rich sandstones. These observations on mineral reactivity are used to establishreactivity conceptual models for three CO2storage case-studies in saline sandstone aquifers (Ketzin, InSalah and Snøhvit) and a methodology is proposed to evaluate the long-term geochemical reactivityof these saline aquifers as a result of CO2injection. Noticeable differences are obtained between thecase-studies as a function of the initial mineralogy and chemical conditions in the sandstones, whichhighlight that CO2mineral trapping can take place in a given storage site but can be almost absent inother storage sites. Regarding the activity model and the database, the Pitzer interaction model is rarelyused for simulating CO2geochemical behavior in saline aquifers despite the fact that more conventionallyused activity models are not valid for such salinities. A comparison between calculated mineral solubilityevolution with salinity versus experimental data is performed here using both B-dot and Pitzer activitymodels as well as six different databases. This comparison exercise shows that chemical interactionswithin saline solutions can only be reproduced using the Pitzer model, even though Pitzer databasesare still incomplete or are not coherent for a wide range of chemical species and temperatures. Thegeochemical simulations of CO2injection in Ketzin, In Salah and Snøhvit saline aquifers give divergentresults using different activity models and databases. A high uncertainty on the simulation results is thenlinked to the database choice and this study clearly stresses the need for a Pitzer database that can beconfidently used in all physical/chemical conditions found in deep sedimentary aquifers