Tensile effective stresses in hydrocarbon storage caverns

The "no-tensile effective stress" criterion is discussed. It is proven that effective tensile stresses can be generated at a cavern wall after a rapid increase or decrease in pressure. The Etzel K-102 test, performed in Germany more than 20 years ago, is revisited using the notion of effective tensile stresses

Rapid Depresurizations: Can they lead to irreversible damage?

International audienceRapid gas depressurization leads to gas cooling that is followed by slow gas warming when the cavern is kept idle. The decrease in the temperature of gas depends upon the relative withdrawal rate (in %/day), and cavern size and shape. Gas cooling may result in the onset of tensile stresses at cavern walls and roofs that may generate fractures or cracks. However, in most cases, the depth of penetration of these fractures is small, and they are perpendicular to the cavern wall. The distance between two parallel fractures becomes larger when fractures penetrate deeper into the rock mass, as some fractures stop growing. Fractures form a polygonal pattern. Salt slabs are created, with boundaries formed by the opened fractures. As long as the depth of penetration of the fracture remains small, these slabs remain strongly bonded to the rock mass, and it is believed that, in many cases, their weights are not large enough to allow them to break off the cavern wall

A simplified solution for Gas Flow during a Blow-out in an H2 or air storage cavern

International audienceA small number of blow-outs from gas storage caverns (for example, in Moss Bluff, Texas and Fort Saskatchewan, Canada) have been described in the literature. Gas flow lasted several days before the caverns were empty. In this paper, we suggest simplified methods that allow for computing blow-out duration and evolution of gas temperature and pressure in the cavern and in the well. This method is used to compute air flow from a shaft mine, an accident described by Van Sambeek (2009). The case of a hydrogen storage cavern also is considered, as it is known that hydrogen depressurization can lead, in certain cases, to hydrogen temperature increase

Nouvelles problematiques posees par le cyclage thermo-mecanique en cavites salines

Storage of natural gas in salt caverns had been developed mainly for seasonal storage, resulting in a small number of yearly pressure cycles and moderate gas-production rates. The needs of energy traders are changing towards more aggressive operational modes. The "high-frequency cycling" operation of salt caverns raises questions concerning the effects of frequently repeated and intense mechanical and thermal loading. These questions concern the constitutive creep laws for salt, laboratory test procedures, criteria to be used at the design stage to provide operability, and the long-term integrity of the underground salt caverns.Comment: in French, JNGG 2012, Bordeaux : France (2012

Une mesure de la perméabilité et du fluage d'une caverne dans le sel

Rock mass properties diff er significanùy from those measured on sam pies in the laboratory. A test has been performed on a deep brine-fi.lled ca vern, with the objective of measuring the equilibrium pressure reached when the ca vern was closed. Such an equilibrium is reached when salt mass creep, which leads to cavern shrinkage, balances brine permeation through the ca vern wall. A K = 2·10-19 m 2 value of the average in situ intrinsic permeability has been deduced from the test; it is significantly higher than the intrinsic permeability measured in a weil or in the laboratory. This result supports ca vern abandonment scenarios in which the risk of natural fracturation due to high brine pressures is alleviated.Les propriétés d'un massif rocheux sont en général différentes de celles mesurées au laboratoire sur un échantillon. On a cherché la pression d'équilibre à laquelle se stabilise la saumure contenue dans une cavité souterraine profonde fermée. Cet équilibre résulte de l'action du fluage du massif, qui tend à refermer la cavité, et de la perméation de la saumure à travers les parois de la cavité. On déduit de la valeur d'équilibre mesurée une perméabilité intrinsèque moyenne de l'ordre de $K = 2·10^{-19}\text{m}^2$, sensiblement plus forte que les valeurs estimées antérieurement sur des échantillons ou dans un puits. Ce résultat permet de construire un scénario du comportement de la caverne après abandon, qui exclut le risque de fracturation naturelle

Very slow creep tests on rock samples

International audienceTwelve years ago, creep tests at very low deviatoric stress were performed on an Etrez salt sample in the Varangéville Mine. Recently, a new testing campaign was performed on various salt samples to gain further insight on salt behavior. Creep tests are performed under a 0.1 MPa uniaxial loading on rock-salt samples from the Varangéville and Avery Island Mines and under a 0.24 MPa uniaxial loading on a crushed-salt sample. To minimize the effects of temperature variations, testing devices were placed in an underground mine room, where temperature fluctuations are of the order of one-hundredth of a degree Celsius. The me-chanical loading is provided by dead weights. The deformations were measured through special displacement sensors with a resolution of 1/80 µm. A typical steady-state strain rate reached after 6 months is -2.4 × 10-12 s-1. The influence of air hygrometry, which is approximately 74%RH in the mine, is smaller than expected

Abandon des mines de sel: faut-il en noyer?

L’abandon d’une mine de sel sèche soulève un problème très particulier en raison de la forte probabilité que la mine soit noyée après son abandon, avec des conséquences significatives à la surface du sol. On analyse plusieurs cas d’ennoyage survenus pendant que des mines de sel étaient encore actives, afin de comparer les avantages et les inconvénients d’un ennoyage délibéré avant l’abandon, et notamment la dégradation possible des bancs marneux situés au mur de la mine