Abstract: There is provided a method of drilling an oil or gas well, comprising drilling a wellbore into an underground formation in which a drill bit at the lower end of a drill pipe is placed at the bottom of the wellbore; pumping a first drilling fluid into the wellbore; determining the producing zone of the underground formation; and introducing a second drilling fluid into the wellbore through the drill pipe when the borehole is within the producing zone of the underground formation, wherein the second drilling fluid is a high density drill-in fluid, having a composition different from that of the first drilling fluid and including a brine system with at least one dissolved monovalent salt and at least one dissolved divalent salt together with a suspension polymer, said drilling fluid having a density of at least about 1.50 g/cm.sup.3 and a plastic viscosity of less than about 50 lbs/100 ft.sup.2.

Abstract: A method of converting sodium bromide brine to ammonium bromide brine and optionally to calcium bromide is disclosed. The method involves introducing ammonia and carbon dioxide into the reactant brine, removing a resulting bicarbonate precipitate, driving off any excess ammonium carbonate, and optionally contacting with lime.