The results are given of the simulation on equivalent materials of the behaviour of underground reservoirs in rock salts designed for the storage of natural gas. The limiting values of the spans of the reservoirs are obtained which provide for the long-time stability of the reservoirs.
On cite des resultats de la creation des modeles sur les materiaux equivalents de la conduit des reservoirs sou terrains dans les depôts de sel de roche affectes pour Ie stockage du gaz naturel. On a recu des valeures Iimites des espacements des reservoirs qui assuraient leur resistance durable.
Es sind die Modellierungsergebnisse angefuehrt die an aquivalenten Materialien des Kavernenverhaltens im Steinsalz erhalten wurden, die der Erdgasspeicherung dienen. Die erhaltenen Grenzwerte der Kavernendurchmesser sind angegeben, bei denen die Langzeitstabilitat gewahrleistet wird.
Underground reservoirs for the storage of hydrocarbons are made in rock salts by means of dissolving through wells. Costs per unit of volume of such reservoirs drop substantially as the volume increases. As the height of a reservoir is determined by the geological conditions at the construction site, the minimum costs correspond to the maximum span. For reservoirs made in homogeneous rock salts, a method has been developed for the determination of a permissible span. This method is based on the concepts of continuum mechanics (SNiP 1985). For a reservoir located in salts including clay partings, the span will be determined by means of theoretical studies and experiments conducted on models made from equivalent materials. The use of simulating along with the calculation methods makes it possible to add to the reliability of design approaches to the construction of such critical structures. This study has been carried out to facilitate the construction of an underground gas storage in Russia's Perm region. It is contemplated to make more than one reservoir in this place. Each reservoir will be a body of revolution of a generatrix about a vertical axis normal to the earth's surface. The interval between the reservoirs is such that the interference is negligible. Section through the reservoir by a plane passing through the axis of rotation is shown in Fig. 1. A rock salt mass with a reservoir can be simulated with a two-dimensional or a three-dimensional model. As this takes place, a permissible span value obtained with a two-dimensional model is somewhat less than the value obtained with a three-dimensional model. Should correlation be established between the results of a study carried out on such models, it could be used to determine the characteristic reservoir dimensions considering only the results of a study carried out on two-dimensional models.
In the geological section across the area of the construction of the underground reservoirs Tertiary and Quaternary deposits are present. Below the tertiary deposits lie rocks belonging to the ufimian stage of upper division of the Permian system. They are underlain by covering rock salts, potashmagnesium salts, underlying rock salt up to 20 m thick and a "marker clay" bed 1,5 m thick. Below the "marker clay" bed lies rock salt with clay partings 1- 10 cm thick. This salts 160 m thick is contemplated to be environment for the future underground reservoirs. The overlaying strata effectively protect the reservoir construction interval against invasion of aggressive water. The rock salts are represented by seven sorts with a uniaxial compression strength of 16,8 MPa to 32 MPa. Microgranular salts admixed with dolomite and anhydrite have the highest strength, medium-granular salts with weakened crystal bonds have the lowest strength. An exploratory well struck the bottom of the "marker clay" bed at a depth of 410,8 m. Table 1 gives the depths of clay partings in the upper part of the salt bed.
