aqueous solution out of the gas zone to overcome this problem the water used for the injection test can be flushed to surface using gas n 2 or co 2 the gas is injected down the casing annulus and the water is flushed back through the tubing or vice versa this water can also be swabbed back to surface if a permanent packer to isolate the tubing from the casing is in place coil tubing can be used to perform this task if coil tubing or swabbing is not an option after the feed rate with water is performed wait at least 48 hours to allow the pressure in the reservoir to reach the equilibrium before doing the application once the water is displaced a feed rate for gas should then be established a gas such as nitrogen gas n 2 carbon dioxide co 2 or the like gas is then injected the volume of gas e g n 2 will be calculated to flush all the fluids out of the tubing and or annulus and to establish gas saturation and to ensure permeability in the near well bore matrix the presence of fine clays in proximity to the well bore due to migration of the clay fines during production towards the bore may plug permeability and impede the flow of the water blocking agent a pressure increase during injection of the n 2.