Invert emulsion compositions including an oleaginous, a non-oleaginous and an amine surfactant that are useful in the oil and gas well drilling art are disclosed. The amine surfactant is selected so that the invert emulsion can be converted form a water-in-oil type emulsion to a oil-in-water type emulsion upon the protonation of the amine surfactant. Deprotonation of the amine surfactant reverses the conversion. This solution also permits the conversion of oil-wet solids in the fluid into water-wet solids.