INVERT drilling fluids, because of their chemical composition, offer many advantages over water-based fluids. INVERT fluids have a continuous phase of oil and an aqueous interior phase. The interior water phase is normally a brine solution, formulated with calcium chloride (CaCl2) or sodium chloride (NaCl). Typically, the brine is emulsified into the oil in droplets less than a micron in diameter.
INVERT drilling fluids are generally used where drilling problems not easily handled by water-based fluids are expected, or in situations where the invert drilling fluid is more economical. The major advantage offered by invert fluids is increased borehole stability.
INVERT drilling fluids provide excellent rheological, filtration and oil wetting characteristics which are easily adaptable to various pressure, temperature and wellbore conditions. In addition, these fluids are stable in the presence of high electrolyte concentrations, soluble gases and high temperatures.
INVERT drilling fluids are composed of an oil phase, brine phase and specialty additives. Each of these three groups serves important functions in the preparation of a stable invert emulsion (water-in-oil) and in the maintenance of required drilling fluid properties.