Abstract: A method for removing filtercake from a subterranean borehole comprising drilling the borehole with a drilling fluid that includes additives to form a filtercake having an oxidation-degradable component, preferably a polysaccharide. The filtercake is contacted with a clear brine containing bromine or bromate generating agents to degrade the polymers within the filtercake. The brine contains bromide salts and an oxidant capable of delayed oxidation of the bromide to bromine at downhole conditions.

Abstract: A drilling fluid comprising a blend of brine and additives for maintaining rheological properties in a neutral or slightly acidic brine and a method for using the drilling fluid to drill into a producing formation are disclosed. The drilling fluid comprises viscosifying polymer and fluid loss polymer that function in the brine without substantially adversely affecting their properties. The brine is substantially free of insoluble solids. The viscosifying polymer and/or the fluid loss control polymer can be acid soluble. Zinc salts in the form of zinc bromide alone or in a mixture of zinc bromide and calcium bromide are added to increase the density of the brine solution. The viscosifying polymer has pendant amide and sulfonic acid or sulfonate groups. Alternatively or additionally, the viscosifying polymer comprises a polysaccharide. The fluid loss control polymer can comprise a cross-linked, cationic or amphoteric starch. Soluble solids are dispersed in the brine.

Abstract: A composition is provided which comprises a polymer comprising repeat units derived from an unsaturated amide, an N-vinyl lactam, and optionally, a vinyl acid. Also provided is a water-based fluid composition which can be used as drilling fluid wherein the composition comprises calcium chloride and the polymer. Further providing is a process for using a water-based fluid wherein the process comprises contacting a subterranean formation with the water-based fluid composition disclosed above to effect the control of fluid loss of the water-based fluid composition.

Abstract: New drilling fluids have been invented which are invert emulsion fluids comprising an oleaginous liquid, a non-oleaginous liquid, and a protonated amine. Such fluids are acidic and thus useful in drilling wells in which acidic gases such as CO.sub.2 or H.sub.2 S are likely to be encountered and break, i.e. de-emulsify, the drilling fluid.

Abstract: A water-based drilling fluid for use in shale formations having a given average pore size has solutes dissolved therein sized so as to allow the pores of the shale formations to at least partially restrict the solutes. For purposes of enhancing the restriction of the solutes by the shale pores, the dissolved solutes may have different radii. Additional solutes, preferably lower molecular weight salts, are dissolved in the drilling fluid to lower the activity of the water in the water-based drilling fluid.The same combination of additives, a first additive of dissolved molecular solutes sized to at least partially block a shale pore space and a second additive of dissolved molecular solutes selected to lower the water activity, are combined in a water-based carrier fluid and used in earth boreholes surrounded by shale formations as either a spotting fluid, or as a lubricant, or as a shale formation strengthener or as a completion fluid.

Abstract: The present invention is directed to an aqueous foamed Drilling Fluid for drilling well bores into a subterranean formation, comprising water, at least one clay and at least one foaming agent. According to the invention, it further comprises at least one metal hydroxide. The invention further relates to a method for preparing said foamed drilling fluid.

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: Reduction of the adhesion of polyethercyclicpolyol (PECP) to metals by preparing the PECP by condensing polyol molecules by reactive distillation and replacing part of the polyol with an alcohol of lower hydroxyl content than the polyol.

Abstract: The invention provides brine based well drilling and servicing fluids which exhibit relatively thermally stable rheological and filtration characteristics. The fluids comprise a brine, an amorphous silica viscosifier, a biopolymer viscosifier, a fluid loss control additive, and a bridging agent. By utilizing both a silica viscosifier and a biopolymer viscosifier to provide the desired rheological characteristics, the fluids have enhanced thermal stability thus maintaining their suspension and hole cleaning properties over an extended temperature range.

Abstract: Disclosed is a composition comprising a water swellable clay, and particularly a sodium montmorillonite clay such as bentonite, sodium carbonate, and a water-soluble biopolymer, and particularly a xanthan biopolymer. The composition when mixed with fresh water forms an aqueous drilling mud having the desirable fluid properties including a high gel strength profile of 10-second/10-minute/30-minute gel and a low API fluid loss for use in trenchless directional drilling including mini-horizontal directional drilling, guided boring, auger boring, pipe jacking, microtunneling, and river crossing. The composition mixed with an aqueous medium provides a water-based drilling mud applicable to trenchless directional drilling in an unconsolidated formation and particularly in an environment contaminated with salty water such as sea water. The composition contains a mixture of about 91 to 98% by weight of Wyoming bentonite, about 1 to 8% by weight of carbonate salt of alkali metal, and about 0.

Abstract: The use of a water external micellar dispersion as a drilling fluid for rotary and horizontal drilling operations wherein the drilling fluid contains more than 50% oil in the internal phase, improved high temperature stability, high yield points, low gel strengths, and ultra low fluid loss.

Abstract: Reducing the adherence of polyethercyclicpolyol to metal by exposing the metal to a selected surfactant.

Abstract: Aqueous compositions for use as drilling fluids or as workover fluids/completion fluids comprise calcium chloride and calcium nitrate. The compositions have a density of at least 1.35 g cm.sup.-3 and the weight ratio of calcium chloride to calcium nitrate is 5:95 to 95:5. The compositions may be formulated so as to have low crystallisation temperatures. Additional densifying agents such as calcium bromide and/or zinc bromide may also be included.

Abstract: The invention provides methods for (1) reducing the fluid loss of and (2) reducing the concentration of polymer required to provide a desired degree of fluid loss control to, a well drilling and servicing fluid which contains at least one polymeric viscosifier, at least one polymeric fluid loss control additive, and a water soluble bridging agent suspended in an a liquid in which the bridging agent is not soluble, the methods comprising adding to the fluids a particulate, water soluble, ultra fine filtrate reducing agent having a particle size distribution such that at least 90% of the particles thereof are less than 10 micrometers and the average particle size is from about 3 to about 5 micrometers, the ultra fine filtrate reducing agent being insoluble in the liquid.

Abstract: Disclosed are low solids, high density fluids useful as drilling, workover, and completion fluids and the like in oil and gas well operations. The fluids comprise one or more brines having a density greater than about 1500 kg/m.sup.3, a viscosifier which is a high surface area silica, a fluid loss control additive which is preferably a starch derivative, one or more water soluble or acid soluble bridging agents, and, optionally, an alkaline buffer and a polar additive.Also disclosed is an additive for the preparation of low solids, high density fluids which comprises a fumed silica and a bridging agent in a weight ratio of bridging agent to fumed silica from about 2 to about 20, and optionally, an alkaline buffer in a weight ratio of alkaline buffer to fumed silica from about 0.03 to about 2.5.

Abstract: A composition useful for viscosifying a water-based fluid is provided which comprises a metal aluminate such as sodium aluminate, or a blend of a viscosity promoter such as sodium aluminate and a magnesium compound such as magnesium oxide, or a clay such as bentonite and the blend. The water-based fluid can also contain a clay such as bentonite. A process for viscosifying a water-based fluid is also provided which comprises contacting the fluid with the composition described herein. Also disclosed is a process for controlling water loss of a water-based drilling fluid wherein the process comprises contacting the fluid with the composition described herein.

Abstract: The present invention provides methods of cementing a well with a cementing composition utilizing a portion of the fluid used to drill the well as a component of the cementing composition. The methods basically comprise forming a cementing composition, consisting essentially of a cementing precursor composition and a set-activator introducing the cementing composition into the well and permitting the cementing composition to set into a hard mass therein; wherein the cementing precursor composition is the fluid used to drill the well.

Abstract: A drilling and cementing operation is carried out utilizing a universal fluid comprising blast furnace slag, water, a silicate and a retarder, the components of the drilling fluid being chosen so as to have a dual functionality in promoting the drilling fluid and thereafter in being functional constituents of a cementitious slurry.

Abstract: The present invention provides methods of cementing a well with a cementing composition utilizing a portion of the drilling fluid used to drill the well as a component of the cementing composition. The methods basically comprise forming a cementing composition, consisting essentially of a cementing precursor composition, a set-activator, and a portion of the drilling fluid, introducing the cementing composition into the well and permitting the cementing composition to set into a hard mass therein.

Abstract: A composition suitable for drilling and cementing comprising coal slag, water and drill solids, the components of the drilling fluid being chosen so as to have a dual functionality in promoting the drilling fluid and thereafter in being functional constituents of a cementitious slurry. Also, a method for drilling using a drilling fluid containing coal slag so as to lay down a filter cake which is settable and which is compatible with a subsequent coal slag cementitious slurry.