Modélisation de l'éruption d'une cavité saline de stockage souterrain d'hydrogène

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Mechanical stability of a salt cavern used for hydrogen storage

International audienceUnderground salt cavern storage is recognised as one of the most suitable technologiesto meet the challenges of the new European energy system. With the advantage of being mostlyimpermeable to gases, salt caverns are currently the only structures used to store hydrogen on amassive scale underground. This paper studies the consequences of a rapid withdrawal of hydrogenon the mechanical stability of a salt cavern. Gaseous hydrogen cooling could generate rock saltdilation, cavern closure and tensile stresses at the cavern wall. Numerical computations using thefinite element method help to evaluate the geomechanical consequences of a rapid depressurisationin a selected cavern for an underground hydrogen storage demonstrator in France

Modélisation de l'éruption d'une cavité saline de stockage souterrain d'hydrogène

International audienceModélisation de l'éruption d'une cavité saline de stockage souterrain d'hydrogèn

Effect of impurities in rock salt samples on laboratory tests - consequences on rock mass representativity

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Stockage souterrain de gaz naturel : étude du comportement d’une cavité saline en cycles rapides de soutirage

International audienceThe natural gas storage in salt caverns requires fast injection/ withdrawal cycles due to the increasing dynamics of the energy market. High rates induce rapid changes in the internal pressure of the stored gas causing important temperature changes inducing rocksalt damage. To experimentally observe this phenomenon, the Starfish project led to initiate and characterize the damage caused by purely thermal stresses (cooling-induced) at the surface of a large bloc of rock in the salt Mine of Varangéville (France, near Nancy). The objective was to determine the type of failure mechanism involved with repeated cooling stages. Since the salt generates Acoustic Emissions (AE) with low attenuation of the stress waves, acoustic monitoring has been chosen as one of the methods to follow the impact of the salt cooling. In addition to thermal and mechanical sensors, an acoustic monitoring device consisting of 16 ultrasonic sensors has been installed on the free surface and in boreholes. It enabled to record and locate a large number of AE (58,426) located with good accuracy (2.5 cm). Those AE can be correlated to the evolution of salt fracturing. Acoustic activity is very intense at the start of each cooling cycle, then it decreases with time to reach a very low level (background) after about 15 days. The average localisation depth reached by the AE is about 90 cm during the first cooling period. For subsequent cooling cycles, this depth is limited to 74 cm. All these results show that the first cooling period is decisive, as it contains the strongest and deepest acoustic emissions. It would have been useful to know whether a first cycle with a lower temperature amplitude could have decreased the maximum amplitude and final depth of the AE. This crescendo approach would be useful for operatorsLe stockage du gaz naturel dans les cavités salines nécessite des cycles de remplissage-soutirage de gaz de plus en plus rapides sur le marché de l’énergie. Ces cycles s’accompagnent de variations rapides de la pression interne du gaz stocké avec des variations importantes de la température qui peuvent endommager le massif de sel à la paroi de la cavité de stockage. Plusieurs études théoriques ont été conduites pour estimer ce type d’endommagement qui peut en résulter dans le sel [1 ; 2]. Pour vérifier expérimentalement cet endommagement, une étude a été conduite afin de refroidir un massif de sel et reproduire les sollicitations du parement d’un stockage de gaz. L’objectif principal était d’initier et de caractériser l’endommagement par des contraintes d’origine purement thermique induites par refroidissement à la surface du massif. Il s’agissait de connaître le type de mécanisme de rupture de la roche, la nature et l’extension des fissures ; et de mettre en évidence ou non des éventuels phénomènes de fatigue du massif avec la répétition des cycles de refroidissement. Le sel a l’avantage d’être très émetteur d’émissions sismo-acoustiques (sismogène) et de présenter une atténuation très faible des ondes sismiques. C’est pour cela que l’écoute acoustique a été choisie pour suivre la fracturation du massif de sel

Survey of thermo-mechanical fracturing in salt. Acoustic monitoring

The natural gas storage in salt caverns requires faster injection cycles / racking due to the increasing dynamics of the energy market. These cycles induce rapid changes in the internal pressure of the stored gas causing important temperature changes that can damage the rock salt mass. Several theoretical studies have been conducted to estimate this type of damage (Brouard et al, 2011; Sicsic and Berest, 2014). To experimentally observe this damage, the Solution Mining Research Institute(SMRI) has cofounded the Starfish project between 2013 to 2016 and led by Storengy in partnership with the Ecole des Mines de Paris, the Salins du Midi and INERIS. The main objective of this project was to initiate and characterize the damage by purely thermal stresses at the surface of a large bloc of salt partially slotted in a rock mass of the salt Mine of Varangéville (France). This was to determine the type of failure mechanism involved, the nature and extent of the cracks induced, as well as amplification of the damage of the solid mass with repeated cooling cycles. The salt being favorable to the generation of Acoustic Emissions (AE) and the propagation of the stress waves, the acoustic monitoring method has been chosen to follow the impact of the salt cooling. In addition to thermal and mechanical sensors, an acoustic monitoring device consisting of 16 ultrasonic sensors has been installed on the free surface and in boreholes. It enabled to record and locate a large number of AE (58426) with good accuracy (2.5 cm). Those AE can be correlated to the evolution of salt fracturing. Acoustic monitoring provided a very good insight in the physics of the damaging process..

Acoustic monitoring of thermo-mechanical tests in a salt-mine

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Insights from an experimental campaign on rock salt and implications at the cavern scale

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