In some waterfloods, oil is produced after breakthrough by being dragged along with the produced water or steam. Such wells will be water shut off candidates only if you can afford to lose this subordinate production.

If a production well has a uniform, high water saturation over the total producing interval, the well is not a good candidate for a produced water reduction treatment. If you shut off the water, you will most likely also shut off the oil.

A polymer gel matrix treatment alone won't improve the water injection profile in a well if the water is injected above fracture pressure. Instead, tail in with something strong to plug the perforations and isolate the formation from high pressure. Cement, solid polymers, or a casing patch might do it.

It takes about a quart of cement slurry to plug a perforation. If you are squeezing more than this, you may be fracturing it away!

If you displace a fluid down tubing with a denser fluid, the heavier fluid may reach bottom first. Use a wiper plug to separate the fluids or change their densities.

Plugged perforations will indicate a poor injection profile in the best of injection intervals. Be on guard against this. You may first want to do a stimulation treatment.

When doing a radioactive injection profile survey, test above and (if possible) below the perforations for an RA indication of fluid flowing up or down behind casing.

Properly abandoning a watered-out production well may be your...