Abstract: One embodiment of the present invention relates to spherical ceramic elements, such as proppants, for maintaining permeability in subterranean formations to facilitate extraction of oil and gas therefrom. The strength of the ceramic element may be enhanced by combining materials having different coefficients of thermal expansion. Methods of making the ceramic elements are also disclosed.

Abstract: Sintered, spherical composite pellets or particles comprising alumina fines, at least one of clay and bauxite and optionally a sintering aid, are described, along with a process for their manufacture. The use of such pellets in hydraulic fracturing of subterranean formations and in grinding is also described.

Abstract: The present disclosure includes a system and method contacting surfaces using swellable elements. In some implementations, an apparatus includes a tubing and a polymer compound. The tubing includes surface and is configured to longitudinally conduit fluid. The polymer compound is adjacent at least a portion the surface of the tubing and operable to expand at least in a radial direction in response to at least an activating agent. The polymer compound comprises nano particles with an aspect ratio at least 2.5.

Abstract: The invention describes a method for decreasing the viscosity of crude oils and residuum utilizing a combination of thermal and acidic treatment. Further, the invention describes a method for making a water-in-oil emulsion, or a solids-stabilized water-in-oil emulsion with a reduced viscosity. The emulsion can be used in enhanced oil recovery methods, including using the emulsion as a drive fluid to displace hydrocarbons in a subterranean formation, and using the emulsion as a barrier fluid for diverting flow of fluids in the formation.

Abstract: Viscoelastic surfactant (VES) gelled aqueous fluids containing water, a VES, an internal breaker, a VES stabilizer, a fluid loss control agent and a viscosity enhancer are useful as treating fluids and particularly as fracturing fluids for subterranean formations. These VES-based fluids have faster and more complete clean-up than polymer-based fracturing fluids. The use of an internal breaker permits ready removal of the unique VES micelle based pseudo-filter cake with several advantages including reducing the typical VES loading and total fluid volume since more VES fluid stays within the fracture, generating a more optimum fracture geometry for enhanced reservoir productivity, and treating reservoirs with permeability above the present VES limit of approximately 400 md to at least 2000 md.

Abstract: A method for reclamation of a brine that includes mixing a brine containing thiocyanates with an oxidizing agent; and allowing for a time sufficient for the oxidizing agent to oxidize at least a portion of the thiocyanates is disclosed. Other methods may also include determining the quantity of unoxidized thiocyanates after the oxidizing treatment.

Abstract: Many methods are provided herein including, in one embodiment, a method comprising: providing a fluid that comprises an acid, crosslinked oxidized xanthan, and optionally, a base fluid; placing the fluid in a well bore penetrating a subterranean formation; and allowing the fluid to acidize at least a portion of the formation or damage contained therein. In another embodiment, herein provided is a fluid for subterranean uses comprising an acid and crosslinked, oxidized xanthan.

Abstract: This invention relates to compositions for the management and treatment of water used for the production of oil and gas products comprising an electro-chemically activated, cation or anion-containing aqueous solution (catholyte or anolyte), and to a system and process for their production. A plant is described for treating water used for petroleum production and products including a water reservoir (15), a salt feed device (19) for creating an aqueous salt solution, an electrolysis device (21) to produce anolyte and catholyte solutions, an anolyte tank (31), a cation tank (32) and an anion holding/transport container (33) from which solution is injected into a petroleum processing, petroleum production enhancement or petroleum product application.

Abstract: An additive that increases the density of fluids used in a wellbore during the construction or repair of oil, gas, injection, water, or geothermal wells comprises In one illustrative embodiment the additive comprises a weighting agent, and more preferably an ultra-fine weighting agent. Another embodiment includes a wellbore fluid containing an ultra-fine weighting agent that has an increased density with improved suspension stability without a significant viscosity increase. The wellbore fluid as described herein has rheological properties comparable to a conventional wellbore fluid. An illustrative embodiment of the claimed subject matter is further directed to a method for making the ultra-fine weighting agent and a method for using such ultra-fine weighting agent in a wellbore fluid. In one preferred embodiment the additive has a particle diameter between 4 ?m to 15 ?m. In another preferred embodiment, the additive has a D50 of approximately 3 ?m (1 ?m to 6 ?m).

Abstract: A method of servicing a wellbore in contact with a subterranean formation, comprising placing into a wellbore a composition comprising a calcium aluminate cement and a polyvalent cation-containing compound, and allowing the composition to set. A method of increasing the thickening time of a calcium aluminate cement comprising contacting the calcium aluminate cement with a polyvalent cation-containing compound. A method of adjusting the thickening time of a calcium aluminate cement comprising contacting the calcium aluminate cement with a polyvalent cation-containing compound and at least one other set modifier.

Abstract: A method is provided for reducing lost circulation when aqueous, oil, or synthetic based drilling fluid is used. The method includes injecting two fluids into the well bore and lost circulation zone. The first fluid is an aqueous liquid containing at least one polymer capable of absorbing water in an alkaline environment. The aqueous liquid has a pH that inhibits at least one polymer from absorbing water. The second fluid contains a hardening composition in a base fluid having a pH sufficient to increase the pH in situ to allow at least one polymer to absorb water and expand with the absorbed water and substantially increase in size to close off the lost circulation zone and allow the hardening composition to create a plug in the well bore and set up.

Abstract: Methods and compositions for use in subterranean operations, and more particularly, additives comprising one or more silicates used to treat tar resident in a well bore, and methods of use, are provided. In one embodiment, the method comprises a method of treating tar resident in a well bore comprising providing a tar-treating additive comprising one or more silicates introducing the tar-treating additive into the well bore; and allowing the tar-treating additive to react with the tar resident in the well bore so as to at least partially reduce the adhesiveness of the tar.

Abstract: A water-based drilling fluid having a polymer latex capable of providing a deformable latex film on at least a portion of a subterranean formation has been discovered to provide reduced drilling fluid pressure invasion when used to drill in shale formations for hydrocarbon recovery operations. A precipitating agent such as a silicate or an aluminum complex (e.g. sodium aluminate) is preferably used in conjunction with the polymer. Typically, the water present contains a salt to form a brine, often to saturation, although the invention may be practiced with fresh water. If a salt is employed, it is often helpful to additionally employ a surfactant, such as a betaine, for example.

Abstract: Fluids viscosified with viscoelastic surfactants (VESs) may have their fluid loss properties improved with the presence of at least one mineral oil in combination with at least one particulate fluid loss control agent that may be an alkaline earth metal oxides, alkaline earth metal hydroxides, transition metal oxides, transition metal hydroxides, and mixtures thereof. The mineral oil may initially be dispersed oil droplets in an internal, discontinuous phase of the fluid. In one non-limiting embodiment, the mineral oil is added to the fluid after it has been substantially gelled. The particulate fluid loss control agent may be added in any order relative to the VES and the mineral oil fluid loss control agent. The mineral oil may enhance the ability of a particulate fluid loss control agent to reduce fluid loss. The presence of the mineral oil may also eventually reduce the viscosity of the VES-gelled aqueous fluid.

Abstract: A monovalent cation containing well fluid composed of an aqueous brine containing at least 0.6 equivalents per liter of a water soluble monovalent cation salt, is substantially free of divalent cations, and an amount of a starch derivative selected such that the well fluid has the following characteristics: (a) a low shear rate viscosity greater than about 5,000 centipoise; (b) a high shear rate viscosity at 511 sec?1 in the range from about 15 to about 70 centipoise measured at 120° F. is described. The fluid may be formulated to be substantially free of xanthan gums and preferably has less than 0.25 lb/bbl of xanthan gum.

Abstract: A composition and method for use in drilling or completing a subterranean well comprising a solids free, high-density brine composed of alkali metal polytungstate and blends thereof. These high-density brines are also useful as wellbore fluids and other non-oilfield fluids requiring high density properties.

Abstract: A thermal insulating fluid contains microspheres of hollow spherical particulates. The presence of the hollow spherical particles improves the thermal insulating properties of the fluid by imparting to the thermal insulating fluid a low heat transfer coefficient. The hollow particulates may be inorganic or organic in nature and include hollow spheres of glass, ceramics and plastics. The thermal insulating fluid is capable of controlling the heat transfer from a production tubing or transfer pipe to one or more surrounding annuli and the environment. In addition to reducing heat transfer in the producing well, heat transfer in the fluid produced from the well is also minimized.

Abstract: A method of processing oilfield weighting agents for pneumatic transference including treating a weight material ore with a chemical additive to produce a treated weighting agent and grinding the treated weighting agent to produce a ground treated weighting agent including a substantially homogenized mixture of the chemical additive and a ground weighting agent. Furthermore, the method includes classifying the ground weighting agent by size, discharging the ground treated weighting agent from the mill, and trapping the ground treated weighting agent in a storage vessel. Also, a method of processing oilfield weighting agents for pneumatic transference including grinding a weight material ore in a mill, wherein the grinding produces a ground weighting agent, and discharging the ground weighting agent from the mill.

Abstract: The present invention provides settable compositions that comprise water and cement kiln dust. The settable compositions optionally may comprise an additive that comprises at least one of the following group: fly ash; shale; slag cement; zeolite; metakaolin; and combinations thereof. The settable compositions optionally may be foamed with a gas. Methods of cementing also are provided that comprise: providing the settable composition; introducing the settable composition into a location to be cemented; and allowing the settable composition to set therein. The location to be cemented may be above ground or in a subterranean formation.

Abstract: Well bore servicing fluids are provided that include a thermally activated viscosification compound. Further, methods of servicing a well bore are provided that include displacing such a servicing fluid into the well bore, wherein a viscosity of the servicing fluid increases as it passes down the well bore due to its temperature increasing. Thus, the viscosity of the servicing fluid is effective to suspend solids therein when the servicing fluid is in the well bore. The servicing fluid may be, for example, a cement slurry, a drilling fluid, a gravel packing fluid, a fracturing fluid, a completion fluid, or a work-over fluid. In an embodiment, the thermally activated viscosification compound includes at least one water-soluble hydrophobically modified polymer comprising a hydrophobic substituent having from about 1 to about 22 carbon atoms.

Abstract: Methods for using rapid setting plugging compositions comprising oil, clay, magnesium chloride, and magnesium oxide powder to seal permeable zones in subterranean formations are provided. The permeable zones may be sealed by passing the plugging composition and water to the subterranean formation. While being exposed to downhole temperatures in a range of from about 0° F. to about 500° F., the plugging composition quickly thickens to form a sealing mass that is substantially impermeable to fluid in less than about 1 minute after contacting the water. It then usually develops an effective amount of compressive strength to prevent it from being washed away within a period ranging from about 5 minutes to about 2 hours at temperatures ranging from about 0° F. to about 500° F.

Abstract: Compositions and methods are given for delayed breaking of viscoelastic surfactant gels inside formation pores, particularly for use in hydraulic fracturing. Breaking inside formation pores is accomplished without mechanical intervention or use of a second fluid. Oxidizing agents such as air, oxygen, persulfates, bromates, peroxides, and others are used. The break may be accelerated, for example with a free radical propagating species, or retarded, for example with an oxygen scavenger. In certain brines, for example bromide brines, certain zwitterionic viscoelastic fluid systems that can decarboxylate and that require an anion-containing co-surfactant undergo delayed degradation if oxygen is present, for example from fluid preparation or in a foam.

Abstract: An acidic viscoelastic surfactant fluid composition is formulated with an acid, for example hydrochloric acid, a cationic surfactant, for example a quaternary amine, and a break-enabling salt, for example NH4Cl. The fluid composition has low viscosity as formulated, undergoes an increase in viscosity as the acid is consumed when it reacts with an acid-reactive material, and returns to approximately the initial viscosity as the last of the acid is consumed. The fluid composition is used as a diverting fluid or as the main treatment fluid in oilfield treatments such as matrix acidizing and acid fracturing.

Abstract: A sealant composition and methods for using the same are disclosed. In an embodiment, a method of servicing a wellbore in contact with a subterranean formation is disclosed. The method comprises placing a sealing agent and a nonaqueous carrier fluid in the wellbore. The method further comprises placing a nonaqueous activating fluid in the wellbore. In addition, the method comprises contacting the sealing agent with the nonaqueous activating fluid to form a sealant composition.

Abstract: A water-based, shear-thinning process fluid comprises bentonite, aluminium hydroxide particles, and salt. The median diameter (by weight) of the aluminium hydroxide particles does not exceed 2 ?m.

Abstract: Wellbore treating fluids that include zeolite, an activator, and an organic acid or salt thereof are provided.

Abstract: Settable drilling fluids that comprise an aqueous-based drilling fluid and cement kiln dust. Methods of cementing in a subterranean formation that comprise providing a settable drilling fluid comprising an aqueous-based drilling fluid and cement kiln dust, introducing the settable drilling fluid into a subterranean formation, and allowing the settable drilling fluid to set in the subterranean formation. Methods of converting an aqueous-based drilling fluid to a settable drilling fluid that comprise providing the aqueous-based drilling fluid, and adding cement kiln dust to the aqueous-based drilling fluid to form the settable drilling fluid. Methods of drilling a well bore and cementing a well bore that comprise drilling a well bore, circulating an aqueous-based drilling fluid in the well bore during the step of drilling the well bore, adding cement kiln dust to the aqueous-based drilling fluid to form a settable drilling fluid, and allowing the settable drilling fluid to set in the well bore.

Abstract: Many methods and compositions are provided. One of the methods provided comprises the steps of: providing an aqueous treatment fluid that comprises a polysaccharide and a dual functional component, the aqueous treatment fluid having a first viscosity; allowing the dual functional component to interact with the polysaccharide such that the viscosity of the aqueous treatment fluid increases to a second viscosity, the second viscosity being greater than the first viscosity; placing the aqueous treatment fluid into a subterranean formation; and allowing the dual functional component to interact with the polysaccharide so as to reduce the second viscosity of the aqueous treatment fluid to a third viscosity, the third viscosity being less than the second viscosity. An example of a composition is a viscosified treatment fluid for treating subterranean formations comprising: an aqueous base fluid and an apparent cross linked reaction product of a polysaccharide and a dual functional component.

Abstract: A delayed gelling system useful in conformance control in the production of petroleum from subterranean formations is disclosed. The gelling system comprises an acidic aqueous solution of acid-soluble or cationic polyacrylamide, an at least partially neutralized acid aluminum salt, an activator comprising a hydroxyl donor, and an optional gel modifier. The gelling system may be pumped into formations with excessive water production and thermally activated in the formation at downhole conditions to form a co-gel of polyacrylamide interspersed in an inorganic gel network to reduce water production.

Abstract: Alkaline earth metal compounds may be fluid loss control (FLC) agents for viscoelastic surfactant (VES) fluids used for fluid loss control pills, lost circulation material pills and kill pills in hydrocarbon recovery operations. The FLC agents may include, but not be limited to oxides and hydroxides of alkaline earth metal, and in one case magnesium oxide where the particle size of the magnesium oxide is between 1 nanometer to 0.4 millimeter. The FLC agent may alternatively be transition metal oxides and/or transition metal hydroxides. The FLC agent appears to associate with the VES micelles and together form a novel pseudo-filter cake quasi-crosslinked viscous fluid layer that limits further VES fluid flow into the porous media. The FLC agent solid particles may be added along with VES fluids. The pills may also contain internal breakers to reduce the viscosity thereof so that the components of the pill may be recovered.

Abstract: A composition and method for breaking down and denaturing friction-reducing compound introduced into the ground during the drilling of oil wells and for destroying other contaminants and biohazards naturally present within and artificially introduced into oil wells, which are formed as a result of the drilling and pumping processes. The composition comprises several species of oxidizing agent compounds that are effective in breaking down hydrogen sulfide produced by bacteria as well as the friction-reducing polymer used during drilling and several other organic compounds.

Abstract: The invention discloses an additive for weighted aqueous slurries to reduce lost circulation during well drilling operations, a method of preparing the additive, and a method of reducing lost circulation utilizing the additive. The additive comprises a hardenable alkaline composition comprising mixtures of diatomaceous earth, finely ground paper, a hydrophobic liquid, micronized cellulose and lime. The hydrophobic liquid decreases the time required to prepare the weighted aqueous slurries, i.e., pills, containing the additive.

Abstract: Zeolite and Class F fly ash compositions are provided for use as cement-free settable fluids such as settable spotting fluids and cementitious compositions.

Abstract: A composition is provided for delivering an organic solvent to a downhole portion of a wellbore for the production of hydrocarbon or to a portion of a pipeline for the transmission of hydrocarbon. The composition comprises: (A) water; (B) a weighting agent; (C) an organic solvent that is immiscible with water; and (D) a surfactant adapted for forming an oil-external emulsion of the organic solvent and the water, wherein the surfactant is unstable to hydrolysis. The composition is formed to be an oil-external emulsion. The density of the composition is formulated to be greater than that of pure water at standard temperature and pressure. A method is provided for delivering an organic solvent to a downhole portion of a wellbore for the production of hydrocarbon or to a portion of a pipeline for the transmission of hydrocarbon. The method comprises the steps of: (A) forming a composition according to the invention; and (B) introducing the composition into the wellbore or into the pipeline.

Abstract: Improved casing strings, and methods of using improved casing strings in subterranean operations, are provided. An example of a method is a method of cementing a pipe string in a subterranean formation. Another example of a method is a method of cementing a pipe string in a well bore. An example of an apparatus is an improved pipe string comprising at least one pipe section; and a delivery system of an activator; wherein the delivery system of an activator is disposed adjacent an outer surface of the at least one pipe section.

Abstract: Fluids, such as completion fluids, containing at least one alkali metal tungstate and optionally at least one chelating agent are described. Methods of removing a filter cake from a well bore surface, which may include one or more alkaline earth metal sulfates, is also described, wherein the method includes contacting the filter cake with the completion fluid of the present invention. A drilling fluid or mud is also described wherein the drilling fluid contains at least one alkali metal tungstate. The drilling fluid preferably further contains at least one emulsifier or surfactant and at least one hydrocarbon-based fluid. The various fluids of the present invention can contain other conventional ingredients and optionally at least one alkali metal formate. The present invention permits the fluids to be essentially solids free due to the use of the alkali metal tungstate.

Abstract: Methods of cementing in a subterranean formation may include the steps of: providing a cement composition comprising a cement, water, and a dispersant comprising a low molecular weight starch that comprises anionic groups; placing the cement composition in the subterranean formation; and allowing the cement composition to set therein. In certain embodiments, improved biodegradable dispersants may include low molecular weight starches having anionic groups.

Abstract: A composition and method are given for self-destructive fluid loss additives and filter cakes in wellbores and subterranean formations. The fluid loss additives and filter cakes are formed from a mixture of particulate solid acid-precursors, such as a polylactic acid or a polyglycolic acid, and particulate solid acid-reactive materials, such as magnesium oxide or calcium carbonate. In the presence of water, the solid acid-precursors hydrolyze and dissolve, generating acids that then dissolve the solid acid-reactive materials. The composition is used in oilfield treatments such as drilling, completion and stimulation where it disappears when it is no longer needed without the use of mechanical means or injection of additional fluids.

Abstract: Improved methods for treating and for fracturing subterranean formations and the fluid compositions are provided. The viscosity of a treating fluid containing gelling agents is broken, even at temperatures of about 250° F. and lower, utilizing an oxidizing breaker and a reducing sugar to activate the breaker.

Abstract: Methods of servicing a wellbore in contact with a subterranean formation include passing an ester-based fluid into the wellbore and reducing a temperature of the ester-based fluid by an amount effective to cause the ester-based fluid to set, e.g., by from about 10° F. to about 20° F. The ester-based fluid includes a water in ester-based oil emulsion, a pH controlling additive, e.g., hydrated lime, in the water-phase, and an emulsifier to stabilize the pH controlling additive. Cooling the ester-based fluid causes the emulsion to destabilize, resulting in the release of the pH controlling additive. This release raises pH of the ester-based fluid by an effective amount to cause it to set. Wellbore servicing fluids comprising the foregoing ester-based fluid may be employed as environmentally friendly sealants or spotting fluids in wellbores.

Abstract: The present invention relates to viscoelastic fluids that contain nanotube structures that may be used advantageously as oilfield stimulation fluids in many different applications, most particularly as a fracturing fluid. Viscoelastic fluid compositions of the present invention include an aqueous medium, a viscoelastic surfactant, an organic or inorganic acids, or salt thereof, organic acid salts, inorganic salts, and a nanotube component. The invention is also called to a methods of treating a subterranean well bores in which the viscoelastic fluid is injected into the wellbore to perform operations such as fracturing, drilling, acid fracturing, gravel placement, removing scale, matrix acidizing, and removing mud cake. Further, a method of preparing a nanotube viscoelastic fluid comprising the steps of effectively mixing a carbon nanotube component into a viscoelastic fluid, and sonicating the mixture in order to incorporate the carbon nanotube component is claimed.

Abstract: A powder composition comprising viscoelastic surfactant forms, in aqueous solution, a viscoelastic wellbore treatment fluid.

Abstract: Provided are methods comprising providing an aqueous polymer dispersion comprising water, an anionic salt, a water-based friction reducing polymer, a polyol, an anionic surfactant, and a nonionic surfactant; mixing the aqueous polymer dispersion with additional water to form an aqueous treatment fluid; and introducing the aqueous treatment fluid into a subterranean formation. Also provided are methods comprising providing an aqueous treatment fluid comprising water, an anionic salt, a water-based friction reducing polymer in an amount sufficient to provide friction reduction without forming a gel, a polyol, an anionic surfactant, and a nonionic surfactant; and introducing the aqueous treatment fluid into a subterranean formation.

Abstract: The invention relates to enhancing the conductivity of fractures in a subterranean formation so as to enhance fluid flow therethrough. In one embodiment, the present invention provides a method comprising: providing a proppant matrix composition, the proppant matrix composition comprising at least a plurality of proppant particulates and at least a plurality of composite particles, the composite particles comprising a degradable material and a filler material; introducing the proppant matrix composition to the fracture so as to form a proppant matrix in the fracture; and allowing the degradable material of the composite particles to degrade so as to form at least one void in the proppant matrix.

Abstract: A circulation loss combination for water-based drilling fluid system(s) comprising: a first amount of alkali metal silicate; a second amount of water insoluble particulate; and, a quantity of water soluble activating agent effective to reduce the pH of the water-based drilling fluid system to a value sufficiently low to form an effective circulation loss structure at a desired period of time after addition to the water-based drilling fluid system.

Abstract: A process for reducing the viscosity of fracturing fluids in downhole oilfield operations is provided. The process comprises contacting a sulfamate stabilized, bromine-based breaker with an aqueous polysaccharide fracturing fluid, with the breaker present in an amount to reduce the viscosity of the fracturing fluid. A composition which comprises a sulfamate stabilized, bromine-based breaker for use in decreasing the viscosity of an aqueous polysaccharide fracturing fluid for use in subterranean oil and gas wells is also provided.

Abstract: A packer fluid is provided for use with a wellbore fluid in an annulus or casing bore, having an aqueous portion which contains additives for preventing corrosion, microbiological activity, salt and scale deposition, and an environmentally-acceptable capping fluid which resides at a top of the wellbore to act as freeze protection and as thermal insulation in a the frost penetration layer. The additives in the packer fluid are particularly selected to exist in the aqueous additive fluid and in the wellbore fluid and to be substantially immiscible with the capping fluid and thereby prevent significant migration of the additives into the capping fluid which would compromise its environmental acceptability.

Abstract: A method is given for treating a subterranean formation penetrated by a wellbore with a viscosified fluid. The fluid contains a solid hydrolysable polyacid that upon dissolution and hydrolysis releases an acid that is a breaker for the viscosifying system. Suitable solid hydrolysable polyacids include polylactic acid and polyglycolic acid. The fluid also contains a pH control agent, present in an amount sufficient to neutralize any acid present in the solid hydrolysable polyacid before the injection and to neutralize any acid generated by the solid hydrolysable polyacid during the injection, so that the acid breaker is not available to break the fluid during the injection. In one embodiment the viscosifier is a viscoelastic surfactant fluid system and the solid hydrolysable polyacid is of a size selected to be a fluid loss additive, for example in fracturing or gravel packing.

Abstract: Improved methods for treating and for fracturing subterranean formations and the fluid compositions are provided. A method presented herein is a method of reducing the viscosity of a viscosified treatment fluid that comprises providing a viscosified treatment fluid that comprises a basic fluid and a gelling agent, providing a breaker composition comprising an oxidizing breaker and a breaker activator that comprises a reducing sugar; and allowing the breaker composition and the viscosified treatment fluid to interact so as to reduce the viscosity of the viscosified treatment fluid.

Abstract: The invention provides well drilling and servicing fluids, and methods of drilling, completing, or working over a well therewith, preferred fluids comprise an aqueous liquid, a water soluble polymer viscosifier (preferably xanthan gum), a polymeric fluid loss control additive (preferably a partially depolymerized partially crosslinked hydroxyalkyl ether derivative of starch or a hydroxyalkyl ether derivative of a partially crosslinked and partially depolymerized starch), a bridging agent comprising a particulate calcined magnesia that has an Activity Index greater than about 800 seconds, and an additive selected from the group consisting of citric acid, alkali metal salts of citric acid, ammonium citrate, and mixtures thereof in an amount sufficient to increase the low shear rate viscosity of the fluids, preferably from about 0.05–5 ppb, most preferably from about 0.15–3 ppb.