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: 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 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 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 modified starch polymer derived from an unmodified starch having an amylopectin content of at least 80% by weight. The starch is modified by crosslinking with epichlorohydrin, the amount of epichlorohydrin crosslinking being equivalent to that which is obtained when a crosslinking reaction is subjected to a Brabender viscosity which reaches a maximum value and then is reduced with further crosslinking from its maximum to a value which is no more than 50% of the maximum value, and is carboxymethylated with a degree of substitution of at least 0.1 carboxymethyl groups per anhydroglucose unit. Fermentation stability is obtained when the degree of carboxymethyl substitution is about 0.4 or more. The modified starch polymer may also be hydroxypropylated. The modified starch polymers provide improved high temperature fluid loss performance when incorporated into well drilling fluids.

Abstract: A composition and a process for treating a subterranean formation are disclosed. The process comprises injecting into the subterranean formation a composition which comprises a polymer, a crosslinking agent, a liquid, optionally a clay, and further optionally a weighting agent wherein the polymer forms a gel in the formation, in the presence of the crosslinking agent.

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: The present invention provides compositions useful for viscosifying aqueous fluids, methods for making them and methods for using them. In one aspect of the invention, inventive compositions comprise a prehydrating alcohol having at least two hydroxyl groups and having a molecular weight of from about 60 to about 600; an inorganic salt; and a polymer. In a preferred aspect of the invention, the viscosifier composition additionally comprises a solvent having a molecular weight of from about 75 to about 1000. According to another aspect of the invention, inventive compositions comprise a prehydrating alcohol; an inorganic salt; and a polymer; and the composition is essentially free from water. Inventive compositions find advantageous use in viscosifying fluids utilized in subterranean drilling activities such as, for example, drilling, drill-in, completion, hydraulic fracturing, work-over, packer, well treating, testing, spacer, or hole abandonment fluids.

Abstract: The invention provides alkaline water base well drilling and servicing fluids which deposit an easily degradable and removable filter cake on the sides of a borehole during well drilling and servicing operations. The fluids contain one or more polysaccharide polymers, sized bridging particles, and a peroxide selected from the group consisting of alkaline earth metal peroxides, zinc peroxide, and mixtures thereof. The fluids deposit a filter cake containing the peroxide.

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 a brine having dissolved therein a zinc salt such as zinc bromide, and optionally one or more additional water soluble salts, a viscosifier which is a high surface area silica, a biopolymer viscosifier, a fluid loss control additive which is preferably a starch derivative, zinc carbonate, and, optionally, an alkaline buffer, a polar additive, and a bridging agent.It has been found that zinc carbonate will increase the low shear rate viscosity of fluids containing a zinc salt dissolved therein. Additionally, the combination of zinc carbonate and zinc oxide as the alkaline buffer provides fluids having increased thermal stability as indicated by the low shear rate viscosity of the fluids.

Abstract: The invention involves biopolymer/oil suspension compositions for the oil service industry, most particularly drilling and completion fluids, which provide such fluids a variety of desirable properties. Biopolymers include water soluble polymers and water swellable polymers. Such biopolymer/oil suspension compositions are essentially mixtures of biopolymers such as cellulosics in an oil medium with a specific anti-settling additive. The invention is particularly directed to providing enhanced anti-settling properties to such biopolymer/oil compositions; that is, the ability of the biopolymer/oil composition to retain the biopolymers in suspension prior to the composition being introduced into drilling and completion fluids. The invention in one embodiment is described as a liquid biopolymer-in-oil additive compositions for use in aqueous-based completion fluids, containing an agent comprising: a) one or more polyamides, and b) hydrogenated caster oils including castorwax.

Abstract: The invention concerns the use of mixed hydroxydes of bivalent and trivalent metals with a three-dimensional spaced-lattice structure of the garnet type to control the thixotropic thickening of aqueous preparations, using swellable clays and/or other swellable layer-silicate compounds of natural and/or synthetic origin as visosity-increasing agents. The preferred garnet-type mixed hydroxydes are catoites of the basic structure Ca.sub.3 Al.sub.2 (OH).sub.12 a minor proportion of whose OH units can be exchanged for acid groups, in particular silicate groups.

Abstract: The present invention relates to a pseudoplastic fluid composition including water, a mixed metal layered hydroxide dispersed in the water to impart preselected rheological properties to the fluid and a fluid loss additive composition including one or more of a carboxymethyl substituted vegetable starch, a carboxymethylated cellulosic compound or mixtures thereof in an amount effective to inhibit loss of fluid and with the degree of substitution being selected so that the carboxymethyl substituted compound is soluble in the fluid at the concentration of use without materially adversely affecting the rheological properties of the fluid and so that the fluid is resistant to fermentation. The improved composition includes a crosslinked carboxymethylated vegetable starch which has a degree of substitution in the broad range from about 0.3 to about 0.8 and in a narrower range of about 0.4 to about 0.

Abstract: The invention provides brine based well drilling and servicing fluids containing a fluid loss control additive selected from the group consisting of (1) a crosslinked ether derivative of a partially depolymerized starch, (2) a partially depolymerized crosslinked ether derivative of starch, or (3) mixtures thereof. The fluid loss control additive provides decreased fluid losses at much lower viscosities than the corresponding starch derivatives which have not been partially depolymerized. This enables their use in fluids at concentrations sufficient to provide excellent filtration control, the fluids having a viscosity sufficient for circulation of the fluids in the borehole. The invention also provides a method of reducing the fluid loss of well drilling and servicing fluids utilizing the fluid loss control additives (1) and/or (2).

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: There is provided a method of drilling an oil or gas well, comprising drilling a wellbore into an underground formation in which a drill bit at the lower end of a drill pipe is placed at the bottom of the wellbore; pumping a first drilling fluid into the wellbore; determining the producing zone of the underground formation; and introducing a second drilling fluid into the wellbore through the drill pipe when the borehole is within the producing zone of the underground formation, wherein the second drilling fluid is a high density drill-in fluid, having a composition different from that of the first drilling fluid and including a brine system with at least one dissolved monovalent salt and at least one dissolved divalent salt together with a suspension polymer, said drilling fluid having a density of at least about 1.50 g/cm.sup.3 and a plastic viscosity of less than about 50 lbs/100 ft.sup.2.

Abstract: A composition useful for viscosifying a water-based fluid is provided which comprises a polymer such as guar gum, a metal compound such as an aluminum compound. The composition can also contain a polymer such as guar gum, a magnesium compound such as magnesium oxide, a metal aluminate such as sodium aluminate or a metal compound such as an aluminum compound, and optionally a fatty acid or salts thereof. The water-based fluid can also contain a clay such as bentonite. A process for viscosifying a water-based fluid and for substantially retaining the viscosity of the 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: Borated starch compositions useful for controlling the rate of crosslinking of hydratable polymers in aqueous media for use in drilling fluids.

Abstract: The invention provides (1) a method of increasing the thermal stability of an aqueous polysaccharide-containing fluid by adding thereto magnesia and a thiosulfate salt; (2) a drilling, completion, or workover fluid comprising an aqueous liquid, a water soluble polysaccharide, magnesia, and a thiosulfate salt; and (3) an additive for increasing the thermal stability of an aqueous polysaccharide-containing fluid which comprises magnesia and a thiosulfate salt in a weight ratio of magnesia to thiosulfate salt from about 0.15/1 to about 6.67/1. The preferred magnesia has an activity index less than 100, most preferably less than 50. The preferred thiosulfate salt is sodium thiosulfate. The preferred polysaccharide is selected from the group consisting of xanthan gum, epichlorohydrin crosslinked starch, carboxymethyl cellulose, and mixtures thereof. The preferred aqueous liquid is a saturated sodium chloride solution.

Abstract: In order to reduce the filtrate of aqueous drilling fluid compositions based on clay minerals containing mixed metal hydroxides, a polysaccharide that is partially etherified with hydroxyethyl and/or hydroxypropyl groups is used as the filtrate-reducing agent.

Abstract: A fluid system has been discovered using a distribution of graded calcium carbonate particle sizes, a biopolymer and a polymerized starch. The biopolymer is a non-ionic polysaccharide of the scleroglucan type. It is important that the calcium carbonate particles be distributed across a wide size range to effectively prevent filtration or fluid loss into the formation. Since the filter cake particles do not invade the well bore due to the action of the biopolymer and starch, no high pressure spike occurs during the removal of the filter cake. This high pressure spike indicates damage to the formation and well bore surface, which damage typically reduces overall permeability of the formation. The rheological properties of the fluid allow it to be used in a number of applications where protection of the original permeable formation is desirable.

Abstract: A fluid is provided for the drilling, workover or completion of a subterranean well comprising an aqueous base, the browning reaction product of a carbohydrate, and a cation. Inversion of non-reducing sugars is effected on selected carbohydrates, with the inversion also catalyzing the browning reaction. Inhibition of continued in-situ browning reaction is provided by the addition of a stabilizer.

Abstract: A fluid is provided for the drilling, workover or completion of a subterranean well comprising an aqueous base, the browning reaction product of a carbohydrate, and a cation. Inversion of non-reducing sugars is effected on selected carbohydrates, with the invention also catalyzing the browning reaction.