Method for Terminating or Reducing Water Flow in a Subterranean Formation

A method for placing an aqueous polymer comprising phenoformaldehyde containing 1-2 weight % of a mixture consisting essentially of sodium bisulphite, sodium metabisulphite and mixtures thereof additionally containing 10 weight % anhydrous sodium sulphate, in the water conduits of the production zone of a gas or oil reservoir to form a barrier to shut off or reduce unwanted production of water, through a well-bore tubing and/or annulus of a well in communication with the production zone of the gas or oil reservoir, comprising:

• injecting water into the production zone to establish an injection rate into the production zone of at least 200 L/min. at a pressure differential in the range of 2 to 5 MPa above ambient formation pressure, injecting N2 or CO2 gas into the formation in a first gas injection in an amount sufficient to displace the water or flushing the water to surface with N2 or CO2 in an amount sufficient to displace the water, injecting the aqueous polymer into the production zone at said established injection rate, injecting N2 or CO2 to displace the aqueous polymer from the well bore into formation, to establish communication to the gas zone and to optimize gas permeability in the production zone.

A method as claimed in claimed 12, in which 1 to 10 m3 of hydrofloric acid is injected at a rate of 200 L/min. followed by 1 m3 of water and followed by 25 m3 of N2 gas at STP.