Abstract: The use is disclosed of at least substantially water-insoluble ethers which are fluid and/or at least plastically deformable at working temperature and have flash points of at least 80° C., of mono- and/or polyfunctional alcohols of natural and/or synthetic origin or corresponding solutions of such ethers in ecologically acceptable water-insoluble oils as the dispersed oil phase of water-based O/W-emulsion drilling fluids which are suitable for the environmentally acceptable development of geological formations and which contain, if desired, insoluble, finely particulate weighting agents for the formation of water-based O/W-emulsion drilling muds and/or further additives, such as emulsifiers, fluid-loss additives, wetting agents, alkali reserves and/or auxiliary substances for the inhibition of drilled rock of high water-sensitivity.

Abstract: Described is the use of ecologically compatible, and more particularly of biologically degradable, oils having flash points of above 80.degree. C. for washing mineral oil-loaded drill cuttings prior to the disposal thereof by off-shore and/or on-shore deposition. For the use as wash oils there are preferred aerobically and/or anaerobically degradable low-viscosity oils are employed which are also suitable for being used as a mixture component of the continuous oil phase of W/O invert drilling fluids.

Abstract: Invert emulsion muds for drilling of gas and oil, which are environmentally safe, and which contain:A. a continuous oil phase composed predominantly of at least one monocarboxylic acid ester of a C.sub.2 C.sub.12 monofunctional alkanol wherein the monocarboxylic acid contains from 12 to 16 carbon atoms and is aliphatically saturated,B. a disperse aqueous phase,C. at least one emulsifier,D. at least one weighting agent,E. at least one fluid loss additive, andF. a mild alkaline reserve.

Abstract: Invert emulsion muds for drilling of gas and oil, which are environmentally safe, and which contain:A. a continuous oil phase composed predominantly of at least one monocarboxylic acid ester of a C.sub.2 -C.sub.12 monofunctional alkalol wherein the monocarboxylic acid contains from 16 to 24 carbon atoms and is olefinically mono- or poly-unsaturated,B. a disperse aqueous phase,C. at least one emulsifier,D. at least one weighing agent,E. at least one fluid loss additive, andF. a mild alkaline reserve.