Method and apparatus for underground storage of ammonia and analogous products

A method of storing underground a product, such as ammonia, which is liquefiable under pressure and which is miscible with water, said method comprising the steps of:

• forming a double skin storage container within a cavity in a water-impregnated underground formation, at a depth such that the hydrostatic pressure of the water in the underground formation is greater than the pressure of storage of the product as a liquid, with said double skins spaced to define an intermediate space, said double skin container comprising an outer skin permeable to water and an inner skin impervious to water,
• supplying said product to said container under pressure such that said product is liquid under storage,
• filling said intermediate space with water, and
• maintaining said water within said intermediate space at a pressure which is lower than the lowest expected pressure of the stored product;
• whereby, since the underground formation is at a hydrostatic pressure which is greater than the pressure of storage, water may pass from the formation through the outer skin into the intermediate space, thereby preventing the stored product from leaking into the surrounding formation, and wherein since the water within the intermediate space is at a pressure less than that of the liquified product within the inner skin, any product leakage is through the inner skin into the intermediate space.