Preparation of viscosifiers for zinc salt workover and completion brines

Claim 1

A viscosified zinc salt brine for use as a well fluid, comprising an aqueous solution of zinc bromide in admixture with calcium salt selected from the class consisting of calcium bromide, calcium chloride, and mixtures thereof, said solution containing sufficient zinc to provide a density of at least 15 pounds per gallon, said brine containing from 1 to 6 pounds per barrel of a treated viscosifier prepared by forming a treating solution comprising an aldehyde reagent dissolved in a solvent carrier, said aldehyde reagent being selected from the class consisting of formaldehyde, aliphatic dialdehydes containing from 2 to 6 carbons, and mixtures thereof, said solvent carrier being selected from the class consisting of organic polar solvents in which said aldehyde reagent is soluble and mixtures thereof with a minor proportion of water, said treating solution containing from 0.5 to 15% by weight of said aldehyde reagent, and contacting said treating solution with a viscosifier suitable for use in well fluids, said viscosifier being in the form of a particulate solid and being selected from the class consisting of hydroxyethylcellulose, xanthan gum, the natural vegetable gums and gelatin, a sufficient amount of said treating solution being used to wet said particulate viscosifier, said viscosifier being maintained is essentially unswollen condition during said contacting.