a method of degrading a blocking gel in a subterranean formation of a well bore is shown in which a gellable blocking fluid is first formed by blending together an aqueous fluid , a hydratable polymer , a suitable crosslinking agent for crosslinking the hydratable polymer to form a polymer gel . the polymer gel may contain an enzyme breaker incorporated within . the cross - linked polymer gel is pumped into the well bore . if required , an externally applied enzyme breaker is added prior to gel degradation . the enzyme breaker is allowed to degrade the cross - linked polymer with time to reduce the viscosity of the fluid so that the fluid can be removed from the formation back to the well surface . the particular enzyme breaker utilized has an activity in the ph range from about 1 . 0 to 8 . 0 and is effective to attack only specific linkages in the cross - linked polymer gel .