Draining well for an underground cavity for storing liquefied gas under pressure

Claim 1

An underground storage facility for storing a liquefied gas under pressure and at ambient temperature, said liquefied gas having a lower density than water and being immiscible with water, said facility comprising: a cavity (1) formed in water-impregnated rock for storing said liquefied gas, the hydrostatic pressure in the rock surrounding the cavity implementing the balancing of the gas liquefaction pressure to establish storage equilibrium, a draining or sump well (2) extending downwardly from a bottom (3) of the cavity for collecting and extracting water which seeps into the cavity from the surrounding rock, said well having an upper portion (9) and a contiguous lower portion (10), said upper well portion having a larger cross-sectional area than said lower well portion, a first tube (6) extending downwardly into the lower well portion for extracting water therefrom, a second tube (5) extending downwardly into the well to a point proximate a junction between the upper and lower well portions for extracting liquefied gas from the facility, and means for filling the second tube with water to a height at which hydrostatic equilibrium is established with the pressure in the cavity to implement the mothballing of the storage facility, the volume of the upper well portion above a lower end of the second tube being greater than the volume of said height of water filled in the second tube.