Solution-mined salt caverns for the disposal of hazardous chemical wastes

Abstract

The need for storage caverns (oil, gas) and depositories (radioactive waste, toxic chemical waste) is rising world-wide. Rock salt (halite) formations are particularly suitable for the construction of cavities for such purposes. Rock salt is practically impermeable to gases and liquids. The solution mining method provides the means for the creation of large storage capacities at economic costs and, due to its favourable geomechanical properties, halite remains stable over long periods of time without support. Moreover, it can be shown that underground depositories in salt are safer from an environmental point of view compared with conventional depositories in shallow ground. Howover, safety analysis has to be carried out in each case based on specific site-investigated data. The geotechnical behavior of rock salt is well-known, with sufficient details for dimensioning purposes. For liquid-filled cavities, long-term sealing from the biosphere is of particular cementation has to be proved and it must be shown that the natural pressure rise in the closed cavity due to long-term convergence does not exceed the frac pressure. It is shown that the risk of hydraulic fracturing can be calculated with the aid of finite element computations. Hydraulic fracturing depends on the height and depth of the cavity as well as on the pressure increase rate.