Methods of using invertible oil external-water internal emulsions in
drilling, hydraulic fracturing, gravel packing and completion and then
inverting the emulsion to a water external-oil internal emulsion are
provided. The methods basically comprise the steps of contacting the oil
external-water internal emulsion with an aqueous acid solution containing
an anionic sulfonate surfactant for preventing aqueous acid
solution-crude oil emulsions and crude oil sludging and a chemical for
preventing the anionic sulfonate surfactant from reacting with the
emulsifier in the oil external-water internal emulsion.