Forced collapse of an insoluble seam during the leaching of underground storage facilities in salt

Abstract

Until recently, the basic trend in the creation of reservoir storage facilities for liquid and gaseous products was the construction of above-ground and embedded holding capacities to which the following series of deficiencies were inherent: high construction cost and significant operating expenses, metal consumption, dependence of the temperature regime of the storage facility on atmospheric and climatic conditions, inability to bring into harmony with mechanical action, blast and fire safety, a large land area expropriated, and the ecological effect on the surrounding region.In recent years, increasing attention has therefore been focused on the construction of underground storage facilities in rock salt.To construct underground storage facilities in salt by the leaching method, the presence of salt deposits 100-200 m thick is required as a function of their unit capacity. These intervals of "pure" salt are rarely encountered in nature.As a rule, there are several seams of nonsaline rock in a salt mass (especially in stratified and lens-type deposits).Official specifications [I] permit the presence of insoluble seams up to 2.5 m thick in the working zone, since it is assumed that with sufficient exposure, seams of these dimensions can be removed over the entire section of the leaching chamber.Self-destruction of thick nonsaline seams is not observed, however, in construction practice.Moreover, spontaneous displacements and local failures of these seams, which are associated with characteristic operating procedures of the storage area (periodic filling or emptying, etc.), may lead to disturbance of normal operation of the system and to emergency shutdown of the storage area on the whole with loss of significant amounts of the product being stored.The problem of the forced collapse of insoluble seams over the entire section of the leaching chamber during construction of a storage facility, especially by blasting, arises in this connection.The first premises regarding the forced collapse of an insoluble seam using blast energy during scouring of storage facilities in salt proposed the use of a hole charge placed inside the seam or on its surface [2]. These methods have not come into practical use in view of the small radius of the failure region.Petryashin et al. [3] have proposed a method for the collapse of an insoluble seam by the blast energy of a gas-air mixture filling a portion of the leaching chamber situated above the seam.In substantiating the method, the authors disregarded the elastic properties of the fluid (brine) filling the lower section of the chamber; the counterpressure in the latter, which develops from the start of seam deformation, is rather high and impedes its failure.Unfavorable conditions for the collapse of an insoluble seam are created in cases where intensive external loading causes it to deform in the direction of the free surface.Technologically, this can be achieved in the following manner.Let there be formed as a result of scouring in the salt mass a certain recess with a radius ...