Method for fragmenting underground formations by hydraulic pressure

A method for enlarging a cavity having a substantially unsupported roof in a subterranean formation comprising the steps of:

• substantially filling the subterranean cavity with liquid;
• increasing hydraulic pressure in the subterranean cavity during a period of at least about two hours, the maximum hydraulic pressure in the subterranean cavity being less than sufficient for lifting overburden above the top of a stress arch over the subterranean cavity;
• decreasing hydraulic pressure in the subterranean cavity during a subsequent period of at least about two hours;
• and
• alternately repeating the increasing and decreasing steps for cyclic flexing of the roof of the subterranean cavity.

A method for enlarging a subterranean cavity having a substantially unsupported roof in a subterranean formation and for exposing a leachable mineral constituent of the subterranean formation comprising the steps of:

• substantially filling the subterranean cavity with a liquid;
• increasing hydraulic pressure in the subterranean cavity during the period of at least about two hours, the maximum hydraulic pressure in the subterranean cavity being less than sufficient for lifting overburden above the top of a stress arch over the subterranean cavity;
• and thereafter
• suddenly decreasing the hydraulic pressure in the subterranean cavity.

A method for in situ leaching of at least one mineral constituent in a subterranean formation comprising the steps of:

• drilling at least one well from the ground surface to a subterranean formation selected for leaching;
• forming a cavity in the subterranean formation adjacent such a well;
• substantially filling the subterranean cavity with a solvent liquid for leaching mineral constituents of the subterranean formation;
• withdrawing a pregnant solution containing at least one dissolved mineral constituent from the subterranean cavity;
• repeatedly cyling hydraulic pressure of liquid in the subterranean cavity between a minimum pressure and a maximum pressure less than sufficient for lifting the overburden between the subterranean cavity and the ground surface, for promoting spallation of formation particles and enlarging the subterranean cavity;
• and
• withdrawing at least a portion of such formation particles with the pregnant solution.

A method for in situ leaching of mineral constituents from a subterranean formation comprising the steps of:

• drilling at least one well from the ground surface to a subterranean formation to be leached;
• forming an initial cavity in the subterranean formation in communication with such a well;
• substantially filling the initial subterranean cavity with a solvent liquid for dissolving mineral constituents from the subterranean formation;
• withdrawing a pregnant solution containing dissolved mineral constituents from the subterranean cavity;
• increasing hydraulic pressure in the subterranean cavity during a period of at least about two hours wherein the maximum hydraulic pressure in the subterranean cavity is less than sufficient for lifting overburden above the top of the stress arch formed over the cavity;
• and thereafter
• decreasing hydraulic pressure in the subterranean cavity for promoting spallation of formation particles into the cavity;
• and
• withdrawing at least a portion of such formation particles from the subterranean cavity.