Abstract: The invention provides water base well drilling and servicing fluids containing a biopolymer viscosifier and a water soluble polyalkylene glycol shale stabilizing additive therein having enhanced thermal stability, as indicated by the low shear rate viscosity at 0.06 sec.sup.-1, the enhanced thermal stability being provided by an amorphous silica viscosifier therein.A method of enhancing the thermal stability of aqueous base well drilling and servicing fluids containing a biopolymer viscosifier and a water soluble polyalkylene glycol shale stabilizing additive therein is disclosed which comprises adding to the fluid an amorphous silica viscosifier.

Abstract: Disclosed are invert oil emulsion drilling fluids in which the internal aqueous phase contains one or more water soluble polyethylene glycols dissolved therein. The fluids are characterized by an elevated low shear rate viscosity, hence excellent suspension properties, an elevated Shear Thinning Index, hence excellent drilling characteristics, and a high shale stability index, hence excellent cuttings stabilization and formation protection. Preferred polyethyleneglycols have a molecular weight from about 500 to about 10,000, preferably from about 1000 to about 10,000. Preferred fluids contain from about 5% to about 40% by weight of the polyethyleneglycol in the aqueous phase, most preferably from about 10% to about 30% by weight. Also disclosed is a method of enhancing the thermal stability of invert emulsion well drilling and servicing fluids which comprises dissolving in the aqueous phase thereof one or more polyethyleneglycols.

Abstract: A well drilling and servicing fluid comprising a brine having dissolved therein a formate salt selected from the group consisting of potassium formate, cesium formate, and mixtures thereof, a biopolymer viscosifier, and a pre-gelatinized amylopectin derivative, and optionally a bridging agent and magnesium oxide. The amylopectin starch derivative is a crosslinked amylopectin starch (waxy) which has been crosslinked to the extent that the viscosity of an aqueous amylopectin starch suspension undergoing crosslinking is within about 25% to about 60%, preferably from about 25% to less than about 50%, of the maximum viscosity which can be obtained, and gelatinized.A process of increasing the low shear rate viscosity at ambient temperatures of the aqueous formate brine which comprises adding to the brine a biopolymer and the pre-gelatinized crosslinked amylopectin starch in amounts such that they interact to synergistically increase the low shear rate viscosity of the brine.

Abstract: The invention provides: (1) a process to enhance the removal of solids such as clays, clay-like solids, and shale solids-drill solids-from the surface of a borehole, the solids being deposited from well drilling, completion, or workover fluids during well servicing operations; and (2) a process to enhance the removal of such solids from screens or other sand control devices present in a borehole. The process comprises contacting the solids with an acidic soak solution containing a polyglycol or mono ether derivative thereof and thereafter contacting the surface of the borehole with a wash solution to remove the solids from the borehole.