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International audienceGeological sequestration of CO2 offers a promising solution for reducing net emissions of greenhouse gases into the atmosphere. This emerging technology must make it possible to inject CO2 into deep saline aquifers or oil- and gas-depleted reservoirs in the supercritical state (P > 7.4MPa and T > 31.1◦C) to achieve a higher density and therefore occupy less volume underground. Previous experimental and numerical simulations have demonstrated that massive CO2 injection in saline reservoirs causes a major disequilibrium of the physical and geochemical characteristics of the host aquifer. The near-well injection zone seems to constitute an underground hydrogeological system particularly impacted by supercriticalCO2 injection and themost sensitive area, where chemical phenomena (e.g. mineral dissolution/precipitation) can have a major impact on the porosity and permeability. Furthermore, these phenomena are highly sensitive to temperature. This study, based on numerical multi-phase simulations, investigates thermal effects during CO2 injection into a deep carbonate formation. Different thermal processes and their influence on the chemical and mineral reactivity of the saline reservoir are discussed. This study underlines both the minor effects of intrinsic thermal and thermodynamic processes on mineral reactivity in carbonate aquifers, and the influence of anthropic thermal processes (e.g. injection temperature) on the carbonates' behaviou

This paper presents the results of a theoretical study on the thermal behavior of a hot water storage system in an aquifer using a single well. It is shown that the storage efficiency and temperature are controlled by a limited number of dimensionless groups that depend on the aquifer's physical characteristics and the storage operating parameters. A numerical model is checked against analytical solutions and is then used to evaluate the variation with time of the well temperature during production periods for symmetrical cycles (production volume and flowrate equal to injection volume and flowrate). From these results, type curves are plotted for several sets of dimensionless parameters, covering the range of practical applications. Effects of unequal injection and production periods, standby periods, and other operating conditions are also investigated. Practical recommendations are made for efficient storage projects. INTRODUCTIONThe depletion of classical resources in fossil fuels combined with high inflation rates has recently enhanced interest in developing the exploitation of alternate energy sources and in improving efficiency in the use of energy in general. Along these lines, hot water storage in permeable geological layers appears particularly attractive, for it provides a way of transferring energy from a period of low consumption where it is being produced, into peak hours or seasons.The most important parameters in a heat storage project are (1) the recovery factor (i.e., the ratio of the quantity of energy recovered to that injected) which determines the project economic feasibility and (2) the energy (or temperature) level in the recovered water and its variation during production, which conditions the type of surface utilization. These parameters depend upon the storage physical characteristics (aquifer reservoir thickness, thermal conductivity, heat capacity, etc.) and operating conditions (production and injection rates, duration of injection and production cycles, etc.).In order to facilitate rapid technical evaluations of heat storage projects, and to assess their economic feasibility without engaging into heavy investments, a general study was undertaken of the various parameters that would influence the behavior of such systems. The study, restricted to the case where the same borehole is used for hot water injection and production, included both a theoretical investigation and a field experiment. The theoretical results, which were used to construct type curves convenient for practical applications, are presented hereinafter. Results and analysis of the field experiment are the subject of a companion paper. ScoPE OF STUDYThe theoretical study is concerned with storage of hot water under liquid phase (sensible energy storage) in relatively deep aqufers. Compared with that in shallow aquifers,• Now with Flopetrol, 245 deep aquifer storage appears advantageous because (1) regional groundwater flow being usually negligible, the injected hot water is not displaced, (2) thickness of overburde...

Ten successive in situ experimental investigations of hot water storage by a single well and a pair of wells (doublet) were conducted in 1976-1977 at Bonnaud, Jura, in a confined aquifer 2.5 m thick. The injected volumes ranged from 500-1700 m 3. Temperature profiles were measured daily in 12 boreholes distributed along two perpendicular axes within 13 m of the injection well. Individual temperatures were measured by ten thermistors placed in the caprock. The results are discussed and used to calibrate two mathematical models. An axisymmetric model allows the calibration of average values of the parameters, while a three-dimensional model is used to determine their spatial variation in the horizontal plane. The latter model leads to the identification of a nonhomogeneous transmissibility field which fully accounts for both hydraulic and thermal contour curves. The models, which were matched against particular experiments, proved accurate when simulating other periods. Evidence is given of the importance to the recovery ratio of thermal dispersion in the aquifer and of the water content of the caprock. In a final section, experimental results of single well storage at Bonnaud, Campuget, and Auburn are compared with general type curves derived in the companion paper. They prove to yield adequate predictions of water temperature during the production phases.

Résumé -Choix et caractérisation de sites géologiques propices à l'installation d'un pilote pour le stockage de CO 2 dans le bassin de Paris (GéoCarbone-PICOREF) -Le projet GéoCarbone-PICOREF avait pour objectif de caractériser des sites propices à la réalisation d'un pilote national de stockage du CO 2 en réservoir géologique perméable. Deux types de réservoir ont été examinés : des aquifères profonds, et des gisements d'hydrocarbures en voie d'épuisement. Les sites devaient être choisis de manière que le pilote puisse tester des problématiques qui concernent les futurs stockages de grande taille. GéoCarbone-PICOREF D o s s i e rOil & Gas Science and Technology -Rev. IFP, Vol. 65 (2010), No. 3 376 Après avoir retraité 750 km de lignes sismiques, et avoir assemblé celles-ci selon six coupes calées sur des données de puits, on a précisé sur la Zone régionale :-les grandes caractéristiques des aquifères concernés ; -la localisation des failles ; -la continuité des couches très peu perméables situées au-dessus des réservoirs. Ces études ont permis de choisir un "Secteur", d'environ 70 × 70 km, au sein duquel on a ensuite affiné l'investigation géologique : 450 km supplémentaires de lignes sismiques, collecte exhaustive des données de puits, caractérisation fine des propriétés réservoir. Des observations de terrain ont été faites sur des roches équivalentes portées à l'affleurement. Un modèle géologique et informatique complet du Secteur a été construit à partir de ces données. Il permet de générer des maillages pour la simulation de divers comportements attendus suite à l'injection de CO 2 (déplacement et dissipation du gaz dans les couches réservoir, modification des pressions et des contraintes, déformation mécanique des terrains, interaction entre l'eau acidifiée et les minéraux, etc.