A mixed formate and bromide brine used in drilling fluids

摘要

The use of a saturated aqueous salt solution, comprising at least one formate salt and at least one bromide salt, in a drilling fluid. Said saturated aqueous salt solution comprises 40-50 % by weight of water and 50-60 % by weight of said salts in a weight ratio formate to bromide of 30:70 to 60:40. Preferred salts are alkali metal formates and bromides. The saturated aqueous salts solution has a density and a total salt content exceeding that of a saturated aqueous solution of said bromide salt.