Abstract: Disclosed is a hydrophilic, water soluble polymer concentrate for addition to aqueous liquids to enhance the properties thereof, particularly to increase the viscosity or decrease the fluid loss of well drilling and servicing fluids, the concentrate comprising a hydrophobic, water insoluble liquid, an organophilic clay suspension agent, the water soluble polymer, and a stabilizing agent comprising one or more acids in an amount from about 0.001% to about 1.5%, one or more anionic surfactants in an amount from about 0.001% to about 1.0%, one or more nonionic surfactants in an amount from 0.001% to about 0.625% and, from about 0% to about 0.75% of one or more water soluble organic liquids, wherein the total concentration of the stabilizing agent is from about 0.1% to about 2.5%, these percentages being based on the weight of the concentrate.

Abstract: Methods of consolidating formations or forming chemical casing or both while drilling are provided. One method of the invention comprises drilling a well bore with a drilling fluid comprised of water, a polymeric cationic catalyst which is adsorbed on weak zones or formations formed of unconsolidated clays, shale, sand stone and the like, a water soluble or dispersible polymer which is cross-linked by a thermoset resin and causes the resin to be hard and tough when cured, a particulate curable solid thermoset resin, a water soluble thermoset resin, and a delayed dispersible acid catalyst for curing the solid and water soluble resins. The drilling fluid forms a filter cake on the walls of the well bore that cures and consolidates the unconsolidated weak zones and formations penetrated by the well bore so that sloughing is prevented and forms a hard and tough cross-linked chemical casing on the walls of the well bore.

Abstract: Low concentrations, 1-10% of potassium salt, especially potassium formate, are used in a drilling fluid in oil production. Preferably they are used with guar derivatives, most preferably carboxymethyl hydroxypropyl guar. The concentration of potassium formate is maintained at the desired level by adjusting the potassium formate to maintain a desired Zeta potential in the circulating drilling fluid. The potassium formate/guar derivative composition may be used in the substantial absence of hydrophilic clay additive.

Abstract: The invention provides an organic diacid anhydride-modified chitosan containing a polar additive comprising water soluble compounds containing one or more hydroxyl groups or one or more amino groups, including compounds containing both hydroxyl and amine groups, having a molecular weight less than about 2000, preferably less than about 1000. The invention also provides fluids useful in various well drilling and servicing operations comprising an alkaline aqueous liquid containing an organic diacid anhydride, chitosan, and the polar additive therein, as well as a method of drilling wells therewith.

Abstract: A brine for use during drilling operations, preferably a completion brine, comprising an amount of a low molecular weight water-soluble organic compound effective to reduce the crystallization point of the brine. The low molecular weight water soluble organic compound can be a variety of compounds, with preferred compounds being ethylene glycol, tripropylene glycol bottoms, and combinations thereof. A method of lowering the crystallization point of the brine using a low molecular weight water soluble organic compound also is provided.

Abstract: This invention provides a water-free oil based fluid polymer suspension composition for use as a rheology modifier and fluid loss reducer in oil or gas well servicing fluids. It has been found that by using white medicinal oil as a carrier, high solids content and environmental friendly anhydrous fluidized polymer suspensions of xanthan gum, cellulose ethers, guar gum and derivatives thereof can be prepared. More specifically, in one aspect, an oil-based fluid polymer suspension (FPS) composition for use in oil or gas well servicing fluids is preferred containing: a) a hydrophilic polymer, b) an organophilic clay, c) a stabilizer, and d) a white medicinal oil having selected properties.

Abstract: Disclosed is a method and gellable composition for decreasing the loss of fluid during well drilling or servicing operations. The gellable composition comprises a superabsorbent polymer in an acidic aqueous liquid in which the superabsorbent is not swellable. Preferably the gellable composition also contains a viscosifier, preferably chitosan. The method is practiced by forming the gellable composition, placing it at the location of fluid loss in a well, and mixing it with a basic aqueous liquid to raise the pH and thus allow the superabsorbent to expand in volume. Advantageously, the superabsorbent, chitosan, and an acid, preferably a solid acid, preferably sulfamic acid, are admixed to form an additive for preparing the gellable composition.

Abstract: The invention relates to a ligand-modified cellulose product comprising cellulose ether, calcium salt and at least one ligand as a chelating agent. The product can be used e.g. in drilling fluids.

Abstract: A drilling fluid comprising a pyruvate-free xanthan, which may be an acetate-free pyruvate-free xanthan, and a high density calcium-based brine. Preferably the pyruvate-free xanthan is a genetically prepared pyruvate-free xanthan. A process for recovering crude oil from an oil-bearing subterranean formation by drilling the formation and using a drilling fluid comprising a pyruvate-free gum and a high density calcium-based brine.

Abstract: Disclosed is a composition for and method of reducing the loss of fluid from well drilling, completion, or workover fluids during well drilling, completion, or workover operations, particularly for reducing or overcoming the lost circulation of drilling fluids. The composition comprises an aqueous liquid containing partially hydrated chitosan particles wherein the chitosan particles have been partially hydrated at a pH less than about 4.5, and wherein the aqueous liquid has a pH of at least about 6.5 such that any further solublizing of the chitosan is prevented. The aqueous liquid, preferably when mixed with a drilling, completion, or workover fluid, is effective in decreasing the loss of such fluids after introducing the partially hydrated chitosan-containing liquid or fluid into the flow passages in a well to which such fluids are being lost.

Abstract: The present disclosure relates to a lubricating composition usable for lubricating an interface between a tire and a safety support mounted on a wheel rim within said tire, and a mounted assembly for an automobile provided with said lubricating composition. The lubricating composition according to the invention comprises an aqueous or non aqueous lubricating agent, and a polysaccharide intended to thicken said lubricating agent. The lubricating agent comprises glycerine in a mass fraction equal to or greater than about 60% of the lubricating agent and the lubricating agent is present in said composition in a mass fraction of between about 95% and 99%. The invention also relates to the lubrication between the support and the tire when traveling on a flat tire, following a drop in inflation pressure within said tire.

Abstract: Disclosed are drilling fluids suitable for use in connection with oil well drilling. The drilling fluids of the invention include in one embodiment a liquid base, an alkyl glucoside, such as methyl glucoside, and a borehole stability agent that includes a maltodextrin, a carboxyalkyl starch, a hemicellulose-containing material, or a mixture of the foregoing. In another embodiment, the drilling fluid includes a liquid base and desugared molasses solids, preferably in combination with an alkyl glucoside and more preferably in further combination with one of the aforementioned borehole stability agents. The drilling fluids of the invention surprisingly have a reduced tendency to swell shale as compared with known drilling fluids. Also disclosed are a drilling apparatus and process. The drilling apparatus includes a drill string, which may be conventional, that is fluidically coupled to a source of drilling fluid, the source of drilling fluid including the drilling fluid of the invention.

Abstract: The present invention relates to the use of a buffered acid wash to reduce the amount of oil in cuttings associated with the use of an invert emulsion well fluid. The buffered acid wash is sufficiently acidic as to convert all of the surfactant in the invert oil emulsion from one charge species into another, but substantially prevents the fluid from becoming so acidic as to generate carbon dioxide.

Abstract: Water-based drilling fluid comprising: (a) water, (b) at least one biopolymer of the polysaccharide type, (c) at least one filtrate reducer selected from starches with different cross-linking degrees in presence of cellulose microfibers, (d) optionally a hydrosoluble polymeric surface-active agent having an HLB from 10 to 16, preferably from 11 to 14.

Abstract: Selectively cross-linked starches are disclosed that are useful as fluid loss control additives in subterranean treatment fluids comprising starches that cross-linked to a Brabender peak viscosity of about 800 to about 1250 Brabender units after about 40 to about 70 minutes at about 92° C. and provide good fluid loss control over a temperature range of from about 20° C. to about 160° C. (68° F. to 320° F.).

Abstract: The invention concerns guar-free fluids capable of being used in oil mining and containing deacetylated xanthan gum in the form of a polypentamer, combined with at least one compound increasing the medium ionic strength. The invention also concerns the use, as filtrate reducer with improved properties, of deacetylated xanthan gum in the form of a polypentamer, combined with a compound increasing the medium ionic strength and a standard filtrate reducer.

Abstract: Clay is stabilized in the drilling of wells for hydrocarbon production by the addition to the drilling fluid of potassium formate together with an amount of guar effective to inhibit clay and shale swelling and sloughing.

Abstract: A new stable liquid suspension containing non-soluble particles dispersed in a non-aqueous liquid medium having a concentration of a suspension aid and a method of making and use thereof.

Abstract: The invention provides an organic diacid anhydride-modified chitosan containing a polar additive comprising water soluble compounds containing one or more hydroxyl groups or one or more amino groups, including compounds containing both hydroxyl and amine groups, having a molecular weight less than about 2000, preferably less than about 1000. The invention also provides fluids useful in various well drilling and servicing operations comprising an alkaline aqueous liquid containing an organic diacid anhydride, chitosan, and the polar additive therein, as well as a method of drilling wells therewith.

Abstract: The invention provides a method and fluid for drilling or servicing a well in a subterranean formation, particularly containing lost circulation zones or depleted, low pressure reservoirs. A method of decreasing the density of the fluid circulated in a borehole, decreasing the invasion of fluid into formations contacted by the fluid, or decreasing the lost circulation potential of the fluid is provided by using as the fluid an aqueous liquid having dispersed therein a polymer which increases the low shear rate viscosity of the fluid to the extent that the shear thinning index of the fluid is at least about 10, a surfactant, and aphrons, wherein the aphrons are preferably generated by the turbulence and pressure drop as the fluid exits the drill bit in the vicinity of the formation, the fluid having a low shear rate viscosity of at least 40,000 centipoise.

Abstract: A process and composition are provided for permeability reduction in a hydrocarbon-bearing formation to improve hydrocarbon recovery therefrom. A moderately epichlorohydrin cross-linked, non-hydroxylpropylated starch is derived from high amylopectin waxy maize starch for use in drilling, workover and completion fluids. The starch is combined with xanthan gum and used in solutions of fresh water, non-saturated brine or saturated brine containing sized salt particles, typically sodium chloride, of various sizes, or sized calcium carbonate, or a combination of sized salt and sized calcium carbonate.

Abstract: The invention provides well drilling and servicing fluids comprising an alkaline aqueous liquid containing chitosan, an anhydride, and an aldehyde therein. The invention further provides a method of drilling a well wherein there is circulated in the wellbore during drilling a drilling fluid comprising an alkaline aqueous liquid containing chitosan and an anhydride, and optionally an aldehyde therein.

Abstract: A chemical system and method to stop or minimize fluid loss during completion of wells penetrating hydrocarbon formations are provided. The inventions relates to formulating a highly stable crosslinked hydroxyethyl cellulose (HEC), control released viscosity reduction additives, and user friendly packaging. The chemical system contains a linear HEC polymer solution, a low solubility compound which slowly raises the fluid pH, a chelating agent which further increases the pH level beyond the equilibrium achievable by the low solubility compound, a metal crosslinker which crosslinks HEC at elevated pH, a crosslink delaying agent which allows fluid viscosity to remain low until the fluid reaches the subterranean formation, and optionally an internal breaker. The chemical additives are packaged as an integrated pallet and transported to a field location which allows operators to conveniently mix them before pumping.

Abstract: Disclosed is a composition for and method of reducing the loss of fluid from well drilling, completion, or workover fluids during well drilling, completion, or workover operations, particularly for reducing or overcoming the lost circulation of drilling fluids. The composition comprises an aqueous liquid containing partially hydrated chitosan particles wherein the chitosan particles have been partially hydrated at a pH less than about 4.5, and wherein the aqueous liquid has a pH of at least about 6.5 such that any further solublizing of the chitosan is prevented. The aqueous liquid, preferably when mixed with a drilling, completion, or workover fluid, is effective in decreasing the loss of such fluids after introducing the partially hydrated chitosan-containing liquid or fluid into the flow passages in a well to which such fluids are being lost.

Abstract: The present invention comprises a stable hydrocolloid composition in which preferably welan gum is uniformly dispersed in a superplasticizer solution such as sulfonated naphthalene, sulfonated melamine, modified lignosulfate, their derivatives and mixtures thereof. The solution is wet milled to form an extremely fine particle size distribution of the gum. The composition is rapidly hydratable and useful as a stabilizing additive in many cement and drilling fluid applications.

Abstract: The invention provides aqueous viscous or gelled alkaline fluids particularly useful in oil and gas well operations, and a method of drilling a well therewith. The fluids contain chitosan, an amine reactive acid, and an aldehyde therein, whereby the amine reactive acid and the aldehyde react with the primary amino group on the chitosan to increase the viscosity and stability of the fluid. The fluids are also useful wherein other chitosan-containing fluids are utilized. The preferred amine reactive acid is glyoxylic acid, and the preferred aldehyde is lactose.

Abstract: Water based drilling fluid compositions which contain at least one viscosity builder and at least one rheological control agent wherein the rheological control agent is an amphoteric polymer, the cationic groups of the amphoteric polymer being quaternary ammonium groups.

Abstract: The present invention discloses a method of producing modified, derivatized chitosans which produce viscous aqueous liquids when dispersed (solublized) in compatible aqueous liquids. The method comprises reacting chitosan in an acidic solution with an aldehyde-group containing chemical modifier at an elevated temperature wherein the concentration of chitosan in the acidic solution and the reaction time at the elevated temperature are sufficient to produce a semi-solid gel. The preferred chemical modifier is one or more saccharides containing less than about 10 saccharide units, most preferably lactose. The preferred reaction temperature is greater than about 60° C., and the preferred concentration of chitosan is at least about 1.43% w/v. The invention also discloses the acidic chitosan-containing concentrates prepared by the method, and the viscous acidic fluids prepared by dispersing/solubilizing the concentrates in aqueous liquids.

Abstract: The invention provides well drilling and servicing fluids and method of drilling a well therewith, the fluids comprising an alkaline aqueous liquid containing chitosan and an anhydride therein, and optionally an aldehyde and/or pyruvic acid therein. The preferred anhydride is succinic anhydride at an anhydride to chitosan weight ratio from about 0.1 to 1 to about 1.5 to 1.

Abstract: The invention provides aqueous viscous or gelled alkaline fluids particularly useful in oil and gas well operations, and a method of drilling a well therewith. The fluids contain chitosan, an amine reactive acid, and an aldehyde therein, whereby the amine reactive acid and the aldehyde react with the primary amino group on the chitosan to increase the viscosity and stability of the fluid. The fluids are also useful wherein other chitosan-containing fluids are utilized. The preferred amine reactive acid is glyoxylic acid, and the preferred aldehyde is lactose.

Abstract: Disclosed are a process for the preparation of pseudoplastic, shear thinning chitosan-containing fluids, and a method of enhancing the thermal stability of such fluids. Pseudoplastic fluids useful oil and/or gas wells, particularly drilling fluids, drill-in fluids, workover fluids, completion fluids, perforating fluids, filter cake removal fluids, various pills, and the like, are prepared by solublizing chitosan in an acidic solution and thereafter raising the pH above about 7.0 by the addition of a basic compound thereto. The thermal stability of such fluids is enhanced by incorporating into the fluids certain aldose or ketose sugars, oligosaccharides of such sugars, and mixtures thereof, optionally together with a water soluble bisulfite compound.

Abstract: A salt water drilling mud comprising a mixture salt water, a solid phase such as pre-hydrated bentonite, attapulgite, sepiolite, and extended bentonite, among others and optionally a synthetic oil, which is mixed with at least one of five different modules. A first module contains caustic, a natural wax and a natural thinner. A second module contains components of the first module and an alkali metal aluminate prepared by reacting the first module with aluminum metal. A third module contains the components of the first module and an alkali metal phosphate and/or alkali metal silicate. A fourth module contains the components of the first module, a saturated or unsaturated carboxylic acid source, a surfactant, and a preservative. The fifth module contains a combination of the first, third and fourth modules.

Abstract: Selectively cross-linked starches are disclosed that are useful as fluid loss control additives in subterranean treatment fluids comprising starches that are cross-linked to a Brabender peak viscosity of about 800 to about 1250 Brabender units after about 40 to about 70 minutes at about 92° C. and provide good fluid loss control over a temperature range of from about 20° C. to about 160° C. (68° F. to 320° F.).

Abstract: Compositions and methods useful in creating boreholes, tunnels and other excavations in unstable soils and earth formations, especially those composed partially or wholly of sand, gravel or other granular or permeable material are disclosed. The fluids include a polymer, and a soluble silicate ion source. The fluids of the invention, when used according to the methods of the invention, have unique dual functionality as excavating fluids and as earth-grouting or soil-hardening compositions.

Abstract: Selectively cross-linked starches are disclosed that are useful as fluid loss control additives in subterranean treatment fluids comprising starches that are cross-linked to a Brabender peak viscosity of about 800 to about 1250 Brabender units after about 40 to about 70 minutes at about 92° C. and provide good fluid loss control over a temperature range of from about 20° C. to about 160° C. (68° F. to 320° F.).

Abstract: A process and composition are provided for permeability reduction in a hydrocarbon-bearing formation to improve hydrocarbon recovery therefrom. A moderately epichlorohydrin cross-linked, non-hydroxylpropylated starch is derived from high amylopectin waxy maize starch for use in drilling, workover and completion fluids. The starch is combined with xanthan gum and used in solutions of fresh water, non-saturated brine or saturated brine containing sized salt particles, typically sodium chloride, of various sizes, or sized calcium carbonate, or a combination of sized salt and sized calcium carbonate.

Abstract: Disclosed are oil-in-water emulsions containing an aqueous continuous phase, an emulsified oleaginous liquid, and an oligosaccharide mixture composed of sugar units selected from the group consisting of arabinose, mannose, galactose, glucose, xylose, and mixtures thereof, and which consists primarily of pentosans, hexosans, and mixtures thereof, containing from one to ten sugar units. The emulsions preferably also contain an alkaline earth metal oxide or hydroxide, preferably lime. The emulsions may also contain aphrons.

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: The invention provides a method and fluid for drilling or servicing a well in a subterranean formation, particularly containing lost circulation zones or depleted, low pressure reservoirs. A method of decreasing the density of the fluid circulated in a borehole, decreasing the invasion of fluid into formations contacted by the fluid, or decreasing the lost circulation potential of the fluid is provided by using as the fluid an aqueous liquid having dispersed therein a polymer which increases the low shear rate viscosity of the fluid to the extent that the shear thinning index of the fluid is at least about 10, a surfactant, and aphrons, wherein the aphrons are preferably generated by the turbulence and pressure drop as the fluid exits the drill bit in the vicinity of the formation, the fluid having a low shear rate viscosity of at least 10,000 centipoise.

Abstract: The present invention comprises a stable hydrocolloid composition in which preferably welan gum is uniformly dispersed in a superplasticizer solution such as sulfonated naphthalene, sulfonated melamine, modified lignosulfate, their derivatives and solution thereof. The mixture is wet milled to form an extremely fine particle size, from about 3 microns to about 500 microns distribution of the gum. The composition is rapidly hydratable and useful as a stabilizing additive in many cement and drilling fluid applications.

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: Surfactant compositions for wellbore operations consisting essentially of a first surfactant selected from the group consisting of alkyl polyglycosides containing alkyl groups containing an odd number of carbon atoms from about 9 to about 13 carbon atoms and a second surfactant selected from the group consisting of alkyl polyglycosides containing alkyl groups containing from about 12 to about 18 carbon atoms and a third surfactant selected from the group consisting of linear ethoxylated alcohols containing from about 8 to 12 carbon atoms and from about 2 to about 8 ethylene oxide groups and a method for formulating such surfactant compositions.

Abstract: The present invention provides a method for suppressing the formation of hydrates during drilling operations under conditions that are conducive to hydrate formation comprising using a water based fluid selected from the group consisting of a drilling, a drill-in, and a completion fluid, wherein said water based fluid comprises as an integral component a hydrate suppressing amount of a water-soluble organic compound having a molecular weight below about 800 and said fluid has effective rheology and fluid loss control properties.

Abstract: A fluid selected form the group consisting of a drilling, a drill-in, and a completion fluid, said fluid comprising a substantially linear heteropolyglycol in an amount effective to perform a function selected from the group consisting of polymer stabilization, shale stabilization, and a combination thereof. The fluid preferably comprises water as a continuous phase, and the heteropolyglycol preferably consists essentially of monomers selected from the group consisting of ethylene oxide and linear alpha-omega alkylene diols.

Abstract: A chemical system and method to stop or minimize fluid loss during completion of wells penetrating hydrocarbon formations are provided. The inventions relates to formulating a highly stable crosslinked hydroxyethyl cellulose (HEC), control released viscosity reduction additives, and user friendly packaging. The chemical system contains a linear HEC polymer solution, a low solubility compound which slowly raises the fluid pH, a chelating agent which further increases the pH level beyond the equilibrium achievable by the low solubility compound, a metal crosslinker which crosslinks HEC at elevated pH, a crosslink delaying agent which allows fluid viscosity to remain low until the fluid reaches the subterranean formation, and optionally an internal breaker. The chemical additives are packaged as an integrated pallet and transported to a field location which allows operators to conveniently mix them before pumping.

Abstract: Disclosed are oil-in-water emulsions containing an aqueous polysaccharide-containing continuous phase, an emulsified oleaginous liquid, and an oligosaccharide mixture composed of sugar units selected from the group consisting of arabinose, mannose, galactose, glucose, xylose, and mixtures thereof, and which consists primarily of pentosans and hexosans containing from one to ten sugar units. The emulsions preferably also contain an alkaline earth metal oxide or hydroxide, preferably lime. The emulsions may also contain aphrons. Also disclosed is a method of increasing the low shear rate viscosity of aqueous polysaccharide-containing fluids which comprise incorporating into the fluids an oligosaccharide mixture, an oleaginous liquid, and optionally, an alkaline earth metal oxide or hydroxide.

Abstract: A drilling fluid additive for controlling solids comprising a carrageenan material, such as iota or kappa carrageenan. The drilling fluid additive may be used with other additives, such as a polyacrylate dispersant. Among other things, the drilling fluid additive may be used to drill deviated or horizontal wells, or wells having large diameter boreholes.

Abstract: A dry mix additive, which is used to form a clay-free, i.e., non-argillaceous, inorganic salt-free, i.e., non-brine, biodegradable and chemically degradable aqueous-based wellbore fluid, which is capable of imparting non-Newtonian, pseudoplasticity and fluid loss controlling properties to aqueous systems for use in horizontal directional drilling, finding utility in horizontal environmental well installation for soil and groundwater remediation. The dry mixture comprises (1) from about 80-90 by weight of pre-gelatinized corn starch heteropolysaccharide, and (2) from about 10-20 by weight of a synthetic biopolymer such as Xanthan gum treated with a dispersing agent (glyoxal) for ease of dispersion. Sodium hypochlorite can be added, if desired, to the wellbore fluid to provide resistance to bacterial attack. The dry mixture is added to either fresh water or acidic water in amounts of 12-15 pounds of the dry mixture to a barrel (42 U.S.

Abstract: A plugging liquid for plugging of a zone of a subterranean formation around a drill hole, consisting of an emulsion comprising (a) a continuous phase containing a hydrophobic liquid, an emulsifier and a crosslinking agent for a polysaccharide, and (b) a discontinuous phase containing water and a polysaccharide. A variant of the plugging composition contains in addition a weighting material in the discontinuous phase. Also described is a method for preparing the plugging liquid and a method for plugging a zone of a subterranean formation penetrated by a drill hole in fluid communication with the zone, according to which method the new plugging liquid is injected into the zone via the drill hole and is subjected to high shear forces in the drill hole, whereby the polysaccharide and the crosslinking agent are brought into contact with one another with resulting initiation of a crosslinking of the polysaccharide and the crosslinking agent and a setting of the plugging liquid.

Abstract: Disclosed is a method of increasing the thermal stability or decreasing the fluid loss of aqueous polysaccharide-containing fluids which comprises incorporating into the fluids an oligosaccharide mixture composed of arabinose, mannose, galactose, glucose, and xylose sugar units, the oligosaccharide mixture consisting of the water soluble portion of thermally hydrolyzed lignocellulose and consisting primarily of pentosans and hexosans containing from one to four combined sugar units.Preferred fluids contain a biopolymer which increases the low shear rate viscosity of the fluids. Fluids which contain polysaccharides which impart other desirable characteristics to the fluids, such as increased viscosity at higher shear rates, fluid loss control, and the like, also exhibit increased thermal stability upon incorporating the oligosaccharide mixture therein.