Abstract: A method for removing filter cake from a subterranean borehole comprising drilling the borehole with a drilling fluid that includes additives to form a filter cake having an oxidation-degradable component, preferably a polysaccharide. The filter cake is contacted with a clear brine containing a mixture of a persulfate salt in a variable density brine to degrade the polymers within the filter cake. The persulfate mixture breaks down the filter cake in well bores having temperatures ranging from about 65° F. to 165° F. Concentration of the persulfate sets the pace of the reaction.

Abstract: A method for removing filter cake from a subterranean borehole comprising drilling the borehole with a drilling fluid that includes additives to form a filter cake having an oxidation-degradable component, preferably a polysaccharide. The filter cake is contacted with a clear brine containing a mixture of a persulfate salt in a variable density brine to degrade the polymers within the filter cake. The persulfate mixture breaks down the filter cake in well bores having temperatures ranging from about 65° F. to 165° F. Concentration of the persulfate sets the pace of the reaction.

Abstract: A thermally insulating fluid composition comprising a glycol solvent for a viscosifier, a viscosifier, and optionally, an aqueous brine. The glycol may be selected from a propylene glycol, or under excessive heat temperatures, a butylene glycol, which can be used with or without a viscosifier. Viscosifiers can be selected from hydroxy propyl methyl cellulose, xanthan and hydroxy propyl guar and combinations thereof. In one method of producing the thermally insulating composition, a viscosifier is added to an aqueous brine, water is then added to that solution followed by the addition of dry salt of the brine to increase density if necessary. A propylene glycol solvent is added to the resulting solution. The thermally insulating fluid composition insulates substances stored or transported in multi-walled vessels, tanks, piping and thermal units.