Subterranean cavity chimney development for connecting solution mined cavities

A method of connecting two subterranean cavities in a deposit having a potassium chloride-rich stratum that contains sodium chloride and which is disposed above a potassium chloride-lean, sodium chloride-rich stratum, which comprises the steps of:

• (a) drilling adjacent boreholes into the sodium chloride-rich stratum,
• (b) forming a substantially cylindrical chimney in each borehole by injecting aqueous solvent unsaturated with respect to sodium chloride and potassium chloride into the bottom of the borehole and withdrawing solvent enriched in potassium chloride and sodium chloride from the borehole at a level in the deposit that is at least the lowest level at which connection of the cavities is to be effected, said chimney having a diameter larger than the initial borehole and a volume sufficient to prevent inadvertent reduction in thickness during cavity development of the water-immiscible, non-solvent liquid blanket established in step (c),
• (c) introducing water-immiscible, non-solvent liquid having a density lower than the aqueous solvent into said chimneys, therby establishing a reservoir and blanket of said non-solvent on top of the aqueous solvent in said chimneys,
• (d) introducing aqueous solvent into said chimneys below the surface of said blanket and withdrawing enriched solvent from near the bottom of the chimney, thereby expanding the chimneys laterally adjacent to the bottom of the non-solvent blanket and forming subterranean cavities,
• (e) continuing to expand said cavities in the manner described in step (d) while raising the level of the non-solvent blanket in the cavities incrementally as the cavities expand laterally, thereby forming inverted cone-shaped cavities, and
• (f) further expanding the cone-shaped cavities laterally while maintaining the non-solvent blanket in the adjacent cavities at about the same level until the cavities connect.