A novel, invert emulsion fluid useful in the drilling, completion, and workover of subterranean wells has been invented. The new invert emulsion drilling fluid can readily and reversilby be converted from an invert, i.e., water-in-oil emulsion, to a regular, i.e., oil-in-water emoulsion, and back to the original invert emulsion using an acid-base chemical switch.
展开▼