In situ method for sealing undesirable transverse fractures under hydraulic pressure during lithological displacement of an evaporite deposit

In an underground formation containing an evaporite mineral stratum comprising a water-soluble mineral, said evaporite mineral stratum lying immediately above a water-insoluble stratum of a different composition, said formation comprising a defined parting interface between the two strata and above which is defined an overburden up to the ground,

• a method for sealing undesirable fractures in the evaporite stratum during lithological displacement, comprising
• (a) applying a hydraulic pressure which is greater than the overburden pressure at the interface to lithologically displace the evaporite stratum, thereby forming a gap between the strata and exposing a main mineral free-surface, wherein said application of hydraulic pressure is carried out by injecting a lithological displacement fluid for its flow to further induce formation of new undesirable transverse fractures and/or to intersect natural undesirable transverse fractures in the evaporite stratum, thereby exposing minor mineral free-surfaces in said undesirable fractures;
• (b) flowing a sealing agent into the gap and into the transverse fractures;
• and
• (c) maintaining such sealing agent in said gap and said transverse fractures to form a solidified matter inside said transverse fractures and in said gap.