WO2025080544A1

WO2025080544A1 - Drilling fluids including a viscosifier, and related methods

Info

Publication number: WO2025080544A1
Application number: PCT/US2024/050317
Authority: WO
Inventors: Wei Lu; Balakrishnan PANAMARATHUPALAYAM
Original assignee: Schlumberger Canada Ltd; Services Petroliers Schlumberger SA; Schlumberger Technology BV; Schlumberger Technology Corp
Current assignee: Schlumberger Canada Ltd; Services Petroliers Schlumberger SA; Schlumberger Technology BV; Schlumberger Technology Corp
Priority date: 2023-10-09
Filing date: 2024-10-08
Publication date: 2025-04-17
Anticipated expiration: 2026-04-09

Abstract

A drilling fluid for drilling a subterranean wellbore includes water and a viscosifier including a crosslinked polymer comprising a polymer formed from one or more monomers, and a crosslinker comprising a reaction product of a first reactant including a linear amine and a second reactant including an ether including an epoxide group. Related methods of operating a wellbore and drilling fluids are disclosed.

Description

TITLE

DRILLING FLUIDS INCLUDING A VISCOSIFIER, AND RELATED METHODS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims benefit of United States Provisional Patent

Application Serial No. 63/588893 filed October 9, 2023, which is entirely incorporated by reference herein.

BACKGROUND OF THE DISCLOSURE

[0002] Wellbore drilling operations includes drilling a bore in a formation to access reservoirs of hydrocarbons and other subsurface resources. During drilling of a wellbore, various fluids may be circulated through a drill pipe and drill bit and into the wellbore and may subsequently flow upward through the wellbore to the surface. For example, a drilling fluid (e.g., an aqueous-based fluid, such as drilling mud) may be pumped down the inside of the drill pipe, through the drill bit, and into the wellbore. The drilling fluid returns to the surface through the annulus. The drilling fluid may lubricated and cool the drill bit and remove generated formation cuttings. Maintaining a sufficiently high viscosity of the drilling fluid may facilitate providing sufficient suspension and removal of cuttings by the drilling fluid.

[0003] Conventionally, the viscosity of the drilling fluid may be increased with a viscosifier (also referred to as a “thickener”), such as xanthan gum or a polyacrylamide. The higher temperatures encountered downhole and the presence of ions in the drilling fluid may reduce an effectiveness of the viscosifiers. In addition, the drilling fluid may facilitate formation of a filtercake on surfaces of the formation to reduce or prevent permeation of fluids from entering the surrounding formation. However, some filtercakes fail prematurely due to conditions within the formation and wellbore. Other filtercakes may be difficult to break and require significant breakers.

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SLB-Private

SUBSTITUTE SHEET (RULE 26) SUMMARY

[0004] In some embodiments, a drilling fluid comprises water, and a viscosifier comprising a crosslinked polymer comprising a polymer formed from one or more monomers and a crosslinker comprising a reaction product of a first reactant comprising a linear amine and a second reactant comprising one of an ether comprising an epoxide group, and allyl chloride.

[0005] In some embodiments, a drilling fluid comprises a base fluid comprising water, and a crosslinked polymer comprising at least one monomeric unit and a crosslinker comprising a reaction product of a first reactant and a second reactant. The first reactant is selected from the group consisting of ethylene diamine, diallyl amine, and 2,2-oxybis[N- methylethanamine]. The second reactant is selected from the group consisting of allyl glycidyl ether, glycerol triglycidyl ether, and allyl chloride.

[0006] In some embodiments, a method of operating a wellbore comprises pumping a wellbore fluid into a wellbore through an earth formation, and operating a drill bit while pumping the wellbore fluid in the wellbore. The wellbore fluid comprises a base fluid and a viscosifier comprising a crosslinked polymer comprising at least one monomeric unit, and a crosslinked comprising a reaction product of a linear amine and at least one of allyl glycidyl ether, glycerol triglycidyl ether, and allyl chloride.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order to describe the manner in which the above-recited and other features of the disclosure can be obtained, a more particular description will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. For better understanding, the like elements have been designated by like reference numbers throughout the various accompanying figures. While some of the drawings may be schematic or exaggerated representations of concepts, at least some of the drawings may be drawn to scale. Understanding that the drawings depict some example embodiments, the embodiments will be described and explained with additional specificity and detail through the use of the accompanying drawings in which:

[0008] FIG. l is a representation of a drilling system for drilling an earth formation to form a wellbore, according to at least one embodiment of the present disclosure; and

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SUBSTITUTE SHEET (RULE 26) [0009] FIG. 2 is a simplified flow diagram illustrating a method 200 of drilling a wellbore, according to at least one embodiment of the disclosure.

DETAILED DESCRIPTION

[0010] This disclosure generally relates to devices, systems, and methods for wellbore fluid additives for downhole applications, such as mitigation of fluid loss and maintenance of fluid viscosity. The fluid additive may be used in a wellbore fluid, such as a drilling fluid, or drill-in fluids (also referred to as “reservoir drill-in fluids” (RDF)). The fluid additive may be referred to herein as a “viscosifier,” a “fluid loss additive,” or a “fluid loss control agent.” The viscosifier may include a crosslinked polymer comprising the reaction product of one or more monomers and a crosslinker. The crosslinked polymer may comprise a copolymer of two monomers. In other embodiments, the crosslinked polymer comprises a terpolymer, a quaternary polymer, or another polymer formed from more than four monomers. The crosslinker may be formulated and configured to facilitate breaking of the crosslinked polymer responsive to exposure a breaker fluid, facilitating the removal of a filtercake formed from the fluid loss additive.

[0011] The crosslinker may include a reaction product of a first reactant comprising a linear amine (e.g., not including a cyclic amide (e.g., a lactam)) and/or an ether amine, and a second reactant comprising one or more of an ether including an epoxide group and an ether group (e.g., an epoxide group bonded to an ether group) and a linear allyl chloride (e.g., allyl chloride). The second reactant may include a reactive epoxy resin diluent, such as a glycidyl ether. The reaction product may include an ether group (e.g., an oxygen atom bonded to two carbon atoms). The viscosifier formed from the polymerized monomers that are crosslinked with the crosslinker may include crosslinked and branched polymeric materials, including branched and crosslinked copolymers, the copolymers crosslinked with the crosslinker. The viscosifier may be suitable for wellbore fluids used in high temperature high pressure (HTHP) applications and may facilitate a stable viscosity and gel strength when used in wellbore fluids under HTHP conditions. For example, the viscosifier may be stable at temperatures up to about 204°C (about 400°F). The crosslinker may include one or more ether groups. Responsive to exposure to a breaker fluid, the ether

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SUBSTITUTE SHEET (RULE 26) group may be hydrolyzed, breaking the viscosifier and filtercakes crosslinked with the crosslinker.

[0012] The viscosifier may increase the viscosity of the wellbore fluid, facilitating efficient cuttings lifting during drilling operations. In addition, the viscosifier may induce formation of a filtercake between the drill string or casing and the walls of the formation. The filtercake may reduce or prevent loss of the drilling fluid into the formation, such as by permeation, preserving the integrity of the formation. In addition, after the drilling operation is complete, the viscosifier and the filtercake may be removed (e.g., broken) to facilitate completion operations. For example, the ether group of the crosslinker may be broken responsive to exposure to a breaker fluid, facilitating removal of the filtercake and completion of the wellbore.

[0013] FIG. 1 shows one example of a drilling system 100 for drilling an earth formation 101 to form a wellbore 102. The drilling system 100 includes a drill rig 103 used to turn a drilling tool assembly 104 which extends downward into the wellbore 102. The drilling tool assembly 104 may include a drill string 105, a bottomhole assembly (“BHA”) 106, and a bit 110, attached to the downhole end of drill string 105.

[0014] The drill string 105 may include several joints of drill pipe 108 connected end- to-end through tool joints 109. The drill string 105 transmits drilling fluid through a central bore and transmits rotational power from the drill rig 103 to the BHA 106. In some embodiments, the drill string 105 may further include additional components such as subs, pup joints, etc. The drill pipe 108 provides a hydraulic passage through which drilling fluid is pumped from the surface. The drilling fluid discharges through selected-size nozzles, jets, or other orifices in the bit 110 for the purposes of cooling the bit 110 and cutting structures thereon, and for lifting cuttings out of the wellbore 102 as it is being drilled.

[0015] The BHA 106 may include the bit 110 or other components. An example BHA 106 may include additional or other components (e.g., coupled between to the drill string 105 and the bit 110). Examples of additional BHA components include drill collars, stabilizers, measurement-while-drilling (“MWD”) tools, logging-while-drilling (“LWD”) tools, downhole motors, underreamers, section mills, hydraulic disconnects, jars, vibration or dampening tools, other components, or combinations of the foregoing. The BHA 106 may further include a rotary steerable system (RSS). The RSS may include directional

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SUBSTITUTE SHEET (RULE 26) drilling tools that change a direction of the bit 110, and thereby the trajectory of the wellbore. At least a portion of the RSS may maintain a geostationary position relative to an absolute reference frame, such as gravity, magnetic north, and/or true north. Using measurements obtained with the geostationary position, the RSS may locate the bit 110, change the course of the bit 110, and direct the directional drilling tools on a projected trajectory.

[0016] In general, the drilling system 100 may include other drilling components and accessories, such as special valves (e.g., kelly cocks, blowout preventers, and safety valves). Additional components included in the drilling system 100 may be considered a part of the drilling tool assembly 104, the drill string 105, or a part of the BHA 106 depending on their locations in the drilling system 100.

[0017] The bit 110 in the BHA 106 may be any type of bit suitable for degrading downhole materials. For instance, the bit 110 may be a drill bit suitable for drilling the earth formation 101. Example types of drill bits used for drilling earth formations are fixed- cutter or drag bits. In other embodiments, the bit 110 may be a mill used for removing metal, composite, elastomer, other materials downhole, or combinations thereof. For instance, the bit 110 may be used with a whipstock to mill into casing 107 lining the wellbore 102. The bit 110 may also be a junk mill used to mill away tools, plugs, cement, other materials within the wellbore 102, or combinations thereof. Swarf or other cuttings formed by use of a mill may be lifted to surface, or may be allowed to fall downhole.

[0018] In some embodiments, during drilling operations, a drilling fluid may be used to facilitate lubrication and cooling of the bit 110 and removal of earth formation 101 cuttings. The drilling fluid may include one or more additives to impart one or more properties on the drilling fluid. For example, the drilling fluid may include a viscosifier formulated and configured to increase a viscosity of the drilling fluid and form a filtercake on walls of the earth formation 101 defining the wellbore 102.

[0019] The drilling fluid may include a base fluid, the viscosifier, and one or more additional additives. In some embodiments, the drilling fluid comprises an aqueous-based drilling fluid and may be referred to as a “drilling mud.” The base fluid may include water, sea water, brine, or a salt-containing aqueous solution. By way of non-limiting example, the base fluid may include a brine including water and one or more salts (e.g., one or more

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SUBSTITUTE SHEET (RULE 26) organic salts and/or one or more inorganic salts). The one or more salts may provide a desired density to the drilling fluid and may also reduce the effect of the drilling fluid on hydratable clays and shales the earth formation 101.

[0020] The salts may include salts of one or more of sodium, calcium, aluminum, magnesium, zinc, potassium, strontium, and lithium, and salts of one or more of chlorides, bromides, carbonates, iodides, chlorates, bromates, formates, nitrates, oxides, phosphates, sulfates, silicates, and fluorides. In some embodiments, the salt comprises a divalent halide, such as an alkaline earth halide (e.g., calcium chloride (CaCh), calcium bromide (CaBr2)), or a zinc halide. The salt may include cesium formate (HCOOR), sodium bromide (NaBr), potassium bromide (KBr), and cesium bromide (CsBr). The particular composition of the salt may be selected based on compatibility with the earth formation 101 and/or to match the brine phase of the completion fluid.

[0021] The one or more additional additives may include one or more of thinners, gelling agents, shale inhibitors, pH buffers, weighing materials, and other additives that may be suitable depending on the particular operation.

[0022] Wellbore fluid thinners may include lignosulfates, lignitic materials, modified lignosulfonates, polyphosphates, tannin, and polyacrylates. The thinners may facilitate improved eheological properties of the drilling fluid (e.g., a reduction in flow resistance) and a reduction in gel development. In addition, the thinner may reduce a thickness of filtercakes formed by the drilling fluid, counteract the effects of salts, and reduce the effects of water on the earth formation 101.

[0023] Weighting materials (also referred to as “weighting agents”) may include one or more of barite (BaSCL), iron oxide (e.g, Fe2C>3, FesCL), calcium carbonate (CaCCE), magnesium carbonate (MgCCh), manganese oxide (MnsCL), and combinations of thereof. The weighting material may be present in the drilling fluid and facilitate increasing the density of the drilling fluid up to about 2.88 g/cm³ (about 24 pounds per gallon (ppg)).

[0024] The pH buffer may include an amine stabilizer, such as one or more of triethanolamine (C6H15NO3) (TEOA), methyldiethanol amine (C5H13NO2) (MDEA), dimethylethanol amine (C4H11NO) (DMEA), di ethanol amine (C4H11NO2) (DEA), monoethanol amine (MEA), cyclic organic amines, sterically hindered amines, amides of

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SUBSTITUTE SHEET (RULE 26) fatty acid, or other suitable tertiary, secondary, and primary amines and ammonia. In some embodiments, the pH buffer includes magnesium oxide.

[0025] The gelling agent may include one or more of a clay and a crosslinked polyvinylpyrrolidone, an acrylamide copolymer, guar, sodium bentonite, or another material. The shale inhibitor may include one or more of amine tartaric salt, ammonium lauric salt, polyammonium, alkyl diammonium, an amphoteric polymer, an organosilicate polymer, a silicone polymer, or another material.

[0026] As described above, the viscosifier may be formulated and configured to increase the viscosity of the drilling fluid, and to facilitate formation of a filtercake between the drill string 105, casing 107, and liners and the earth formation 101. The viscosifier may include a reaction product of one or more monomers that are crosslinked with one or more crosslinkers.

[0027] The monomers for forming the crosslinked polymer may include one or more of acrylamide, unsubstituted acrylamide, methacrylamide, N-substituted acrylamides (e.g., alkylacrylamides, N-methylolacrylamide, N-isopropylacrylaminde, diacetone acrylamide, N-alkyl acrylamide (where alkyl is Ci to Cu), and N,N-dialkyl acrylamides (where alkyl is Ci (e.g., N,N-diemethylacrylamide) to Cu), N-cycloalkane acrylamides, N-(2-hydroxyethyl) acrylamide, N-isopropyl acrylamide, N-[3-(dimethylamino)propyl] acrylamide), N-substituted methacrylamides, acrylates, metacrylates, acryloylmorpholine (e.g., 4-acryloylmorpholine), acrylic acid, methacrylic acid, N-vinylamides, N-allyl amides, vinyl alcohol, vinyl ethers, vinyl esters, allyl alcohol, allyl ethers, allyl esters, acrylic esters, methacrylic esters, N-vinylformamide, N-vinyl acetamide, N-vinylpyridine, N-vinylpyrrolidone, one or more sulfonated anionic monomers (e.g., one or more of 2- acrylamide-2-methyl-propanesulfonic acid (AMPS®), a trademark of the Lubrizol Corporation (also referred to as acrylamide tertiary butyl sulfonic acid (ATBS)), vinyl sulfonates, styrene sulfonic acid), allyl sulfonates, vinylimidazole, allylimidazole, diallyldimethylammonium chloride, methyl chloride quaternary, lipophilic monomers (e.g., one or more of isobornyl methacrylate, 2-ethyl hexyl acrylate, N-alkyl and N,N- dialkyl acrylamide, and styrene), one or more anionic monomers (e g., one or more of maleic acid, tetrahydrophthalic acid, fumaric acid, acrylic acid), and N-vinyl lactams.

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SUBSTITUTE SHEET (RULE 26) [0028] In some embodiments, the copolymer is formed from and comprises the reaction product of at least one acrylamide monomer and at least one sulfonated anionic monomer. In some embodiments, a ratio of the acrylamide monomer to the sulfonated anionic monomer in the copolymer viscosifier may be within a range of from about 0.5 : 1.0 to about 10.0: 1.0. In some embodiments, the at least one sulfonated anionic monomer comprises acrylamide tertiary butyl sulfonic acid and the at least one acrylamide monomer comprises N-N-dimethylacrylamide.

[0029] The polymer may include at least one monomeric unit (monomer units) (monomeric units) comprising the monomers used to form the crosslinked polymer. By way of non-limiting example, where the polymer comprises a copolymer of the reaction product of at least one acrylamide monomer and at least one sulfonated anionic monomer, the polymer includes first monomeric units of the at least one acrylamide monomer and second monomeric units of the at least one sulfonated anionic monomer.

[0030] The crosslinker may react with backbone of the polymer between different branches of the polymer. In other words, the crosslinker may extend between and bond between one polymer chain of the polymer backbone and another polymer chain of the polymer backbone. In some embodiments, the viscosifier includes a crosslinked polymer and/or a mixture comprising a crosslinked polymer including monomers and the reaction product of the reactants used to form the crosslinker. As described herein, the crosslinker may include one or more ether groups that may be broken responsive to exposure to a breaker fluid to break the viscosifier and filtercakes formed from the viscosifier.

[0031] The crosslinker may include a reaction product of a first reactant comprising a linear amine (e.g., not including a cyclic amide (e.g., a lactam, such as an a-lactam, a 0- lactam, a y-lactam, a 8-lactam, or an e-lactam )) and/or an ether amine, and a second reactant comprising one or more of an ether including an epoxide group and an ether group (e.g., an epoxide group bonded to an ether group) and a linear allyl chloride (e.g., allyl chloride). The reaction product may include an ether group (e.g., an oxygen atom bonded to two carbon atoms) (also referred to as an “ether linkage”). In some embodiments, the ether group is present in the second reactant. The reaction product may include, for example, between one ether linkage and four ether linkages.

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SUBSTITUTE SHEET (RULE 26) [0032] The linear amine may include an amine including two terminal amine groups, at least two unsaturated bonds, or at least one unsaturated bond and at least one terminal amine group. The linear amine may include one or more of methylene diamine (CH6N2), ethylene diamine (C2H8N2), diethylenetriamine (DETA) (C4H13N3), triethylenetetramine (C6H18N4) (TETA), 1,3-diaminopropane (also referred to as “trimethylenediamine) (C3H10N2), tetraehtylenepentamine (C8H23N5), pentaethylenehexamine (CioLhsNe), 1,4- diaminobutane (C4H12N2), another diamine connected by an alkyl group, allyl amine (C3H7N), 3-buten-l-amine (C4H9N), diallyl amine (CeHnN), triallyl amine (C9H15N), tetramethyl ethylenediamine (C6H16N2), and an ether amine (e.g., 2,2-oxybis[N- methylethanamine] (C6H16N2O)). In some embodiments, the linear amine comprises a diamine.

[0033] The ether may include a glycidyl ether and may include a reactive epoxy resin diluent including one or more glycidyl ether groups. In some embodiments, the reactive epoxy resin diluent includes two or more terminal diglycidyl ether groups. By way of non-limiting example, the ether may include one or more of allyl glycidyl ether (CeHioCh), glycerol triglycidyl ether (C9H16O5), trimethylolpropane triglycidyl ether (C15H26O6) (TMPTGE), a diglycidyl ether (CeHioCh), an alkyl glycidyl ether (e.g., glycidyl methyl ether (C4H8O2), ethyl glycidyl ether (C5H10O2), propyl glycidyl ether (C6H12O2), butyl glycidyl ether (C7H14O2)), and an alcohol glycidyl ether (e.g., 1,4-butanediol glycidyl ether (C10H18O4)).

[0034] In some embodiments, the crosslinker comprises a reaction product of a diamine and the ether. The linear amine may include at least one terminal amine group. In some embodiments, the diamine comprises a linear diamine, with the amine groups a terminal ends. In some embodiments, the crosslinker comprises a reaction product of ethylene diamine and allyl glycidyl ether having the chemical structure illustrated below.

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SUBSTITUTE SHEET (RULE 26)

[0035] The reaction product may include the ethylene diamine, wherein one or more of the hydrogen atoms bonded to the nitrogen of the amine group is replaced with the allyl diglycidyl ether, the epoxide group hydrolyzed during the reaction of the ethylene diamine and the allyl diglycidyl ether. In other words, the amine groups may be the center of the reaction product and may be bonded to one or two of the ether groups. The reaction product may include four ether groups.

[0036] A molar ratio of the amine (e.g., the ethylene diamine) to the ether (e.g., the ally glycidyl ether) in the crosslinker may be within a range of from about 1.0:2.0 to about 1.0:4.0. In some embodiments, the molar ratio of the amine to the ether is about 1.0:4.0. In embodiments where the crosslinker comprises less than about 4.0 moles of the allyl glycidyl ether for every 1.0 mole of the ethylene diamine, at least some of the nitrogen atoms in the reaction product are bonded to a hydrogen atom (rather than to an ether group from the allyl glycidyl ether). In other words, one or more of the -CH3CHOHCH2-O- CH2CH=CH groups bonded to the nitrogen atom may be replaced with a hydrogen atom (which may reduce a number of ether groups in the reaction product).

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SUBSTITUTE SHEET (RULE 26) [0037] In some embodiments, varying the ratio of the allyl glycidyl ether to the ethylene diamine may alter the gelling properties of the viscosifier including the crosslinker. For example, increasing the ratio of allyl glycidyl ether to the ethylene diamine may increase the viscosity of the viscosifier compared to embodiments where the ratio is lower.

[0038] In other embodiments, the linear amine comprises a diallyl amine and the ether comprises a triglycidyl ether. In some embodiments, the linear amine comprises diallyl amine and the ether comprises glycerol triglycidyl ether and the viscosifier comprises a reaction product of diallyl amine and glycerol triglycidyl ether and may have the chemical structure illustrated below.

[0039] The reaction product may comprise the ether (e.g., the glycerol triglycidyl ether), and the amines may be bonded to (and extend from) the reactant including the ether group. In some embodiments, the reaction product comprises three ether groups. In some embodiments, the crosslinker comprises three ether groups.

[0040] In some embodiments, the ether (the glycerol triglycidyl ether) is replaced with a common epoxy resin reactive diluent, such as one or more of sorbitol polyglycidyl ether (C9H18O7), neopentylglykol-diglycidyl ether (C11H20O4), 2-ethylhexyl glycidyl ether

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SUBSTITUTE SHEET (RULE 26) (C11H22O2), 1,6-hexanediol diglycidyl ether (C12H22O4), and 1,4-butanediol diglycidyl ether (C10H18O4).

[0041] A molar ratio of the diallyl amine to the ether may be within a range of from about 2.0: 1.0 to about 4.0:1.0. In some embodiments, the molar ratio of the diallyl amine to the ether may be about 3.0: 1.0. In other words, for every about 1 mole of the ether, the crosslinker may include about 3.0 moles of diallyl amine.

[0042] In further embodiments, the crosslinker comprises a reaction product of an ether amine, such as 2,2-oxybis[N-methylethanamine] (CeHielShO), and allyl chloride (C3H5CI). In some embodiments, a ratio of the allyl groups to the 2,2-oxybis[N-methylethanamine] in the crosslinker is about 4.0:1.0.

[0043] The crosslinker may be formed by mixing the reactants together. In some embodiments, the reactants are mixed in the presence of a solvent and a catalyst. By way of non-limiting example, the linear amine and the ether may be mixed in a solvent such as water or tert-butyl alcohol to form a mixture. A catalyst may be added to the mixture. The catalyst may include a strong base, such as sodium hydroxide (NaOH) or another base. The pH of the mixture may be about 12.5 or greater. A temperature of the mixture may be within a range of from about 20°C (about room temperature) to about 60°C, such as from about 20°C to about 30°C, from about 30°C to about 40°C, from about 40°C to about 50°C, or from about 50°C to about 60°C.

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SUBSTITUTE SHEET (RULE 26) [0044] In some embodiments, such as where the reactants comprise 2,2-oxybis[N-methylethanamine] and allyl chloride, the reactants may be mixed in a solvent (e.g., water or tert-butyl alcohol). In some embodiments, the mixture is heated to a boiling temperature of the allyl chloride (about 45°C) and the mixture is refluxed during reaction.

[0045] The viscosifier comprising crosslinked polymers crosslinked with crosslinkers may be formed by polymerization by precipitation. For example, the viscosifier may be formed by providing the first reactant to a reaction vessel (e.g., a jacketed stirred vessel including a distillation column, a stirrer, a gas inlet, and a sparging nozzle) and mixing the first reactant with a solvent (e.g., water, tert-butyl alcohol). After mixing the first reactant with the solvent, the crosslinker may be added to the reaction vessel. In some embodiments, the mixture is sparged (e.g., with nitrogen gas) for a duration (e.g., about one hour) and the mixture is heated to a desired temperature (e.g., within a range of from about 20°C to about 60°C). After reaching the desired temperature, the second reactant may be added to the mixture to initiate the polymerization reaction of the viscosifier and precipitate the viscosifier polymer. After forming the polymer, the solvent may be evaporated under vacuum, resulting in a dry powder comprising the viscosifier.

[0046] The crosslinker may constitute from about 0.1 weight percent to about 5 10.0 weight percent of the viscosifier. For example, the crosslinker may constitute from about 0.1 weight percent to about 1.0 weight percent, from about 1.0 weight percent to about 3.0 weight percent, from about 3.0 weight percent to about 5.0 weight percent, or from about 5.0 weight percent to about 10.0 weight percent of the viscosifier.

[0047] The viscosifier may include the crosslinked polymer formed from monomer units of one or more monomers and the crosslinker. In some embodiments, terminal ends of the crosslinker may react with the backbone of the polymer. For example, where the crosslinker comprising a reaction product of 2,2-oxybis[N-methylethanamine] and allyl chloride, the crosslinked polymer may include, for example, a methylpyrrolidine group at the backbone and have the following structure, the crosslinker bridging between polymer chains of the crosslinked polymer:

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SUBSTITUTE SHEET (RULE 26)

[0048] In use and operation, the viscosifier may be added to a drilling fluid. The viscosifier may increase the viscosity of the drilling fluid and facilitate formation of a filtercake on walls of the wellbore at wellbore conditions. The filtercake may substantially reduce or prevent infiltration of the formation with drilling fluids.

[0049] The viscosifier may be suitable for high temperature high pressure applications and have a temperature stability up to about 204°C (about 400°F), such as up to about 93.3°C (about 200°F), up to about 121.1°C (about 250°F), up to about 148.9°C (about 300°F), or up to about 176.7°C (about 350°F). In some embodiments, the viscosifier is formulated and configured to be stable up to a temperature of about 140.6°C (about 285°F). [0050] After use in a drilling fluid, such as after a drilling operation has been completed, the viscosifier and filtercake may be removed from the wellbore. For example, the viscosifier and the filtercake may be exposed to one or more breaker fluids to remove

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SUBSTITUTE SHEET (RULE 26) the viscosifier and the filtercake from the wellbore. Exposure of the viscosifier and the filtercake to the breaker fluid may hydrolyze the one or more ether linkages of the crosslinker of the viscosifier and the filtercake to break the viscosifier. Accordingly, breaking the viscosifier and the filtercake may be performed by reacting the one or more ether linkages of the crosslinker of the viscosifier, such as in a hydrolysis reaction. The viscosifier may be hydrolyzed by exposure to one or more of an acid, an oxidizer, and an acid.

[0051] The breaker fluid may include one or more of an acid, an oxidizer, and a solvent. The acid may include one or more of a strong mineral acid (e.g., hydrochloric acid, sulfuric acid), organic acids (e.g., citric acid, salicyclic acid, lactic acid, malic acid, maleic acid, acetic acid, formic acid, glycolic acid, fumaric acid, and homo- or copolymers of lactic acid and glycolic acid.

[0052] The oxidizer may include one or more of ammonium persulfate, THBP, a peroxide, a hydrolysable esters of carboxylic acid, a hydrolysable phosphonic ester, or a hydrolysable sulfonic ester. By way of non-limiting example, the hydrolysable esters of carboxylic acid may include one or more of a Ci to a Ce carboxylic acid, a C3 to G of a di carboxylic acid, a C2 to C30 mono- or poly-alcohol (including alkyl orthoesters). In some embodiments, the hydrolysable esters include about 57 weight percent to about 67 weight percent dimethyl glutarate, about 18 weight percent to about 28 weight percent dimethyl succinate, and 8 weight percent to about 22 weight percent dimethyl adipate. In other embodiments, the oxidizer comprises one or more of RJtEPCh, R¹R²HPO3, R^R^Ch, R^SOs, R¹R²SO₃, R¹H₂PO₄, R¹R²HPO₄, R¹R²R³PO₄, R¹HSO₄, or R¹R²SO₄, where R¹, R², and R³ are C₂ to C30 alkyl-, aryl-, arylalkyl-, or alkyl aryl -groups.

[0053] The breaker fluid may further comprise an oxidant formulated and configured to react with a polymer and disrupt the filtercake. The oxidant may include a bromates, peroxides (including peroxide adducts), other compounds including a peroxy bond such as persulfates, perborates, percarbonates, perphosphates, and persilicates, and other oxidizers such as hypochlorites. In one or more embodiments, the oxidant may be included in the breaker fluid in an amount from about 1 ppb to 10 ppb.

[0054] FIG. 2 is a simplified flow diagram illustrating a method 200 of operating a wellbore, according to at least one embodiment of the disclosure. The method 200 includes

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SUBSTITUTE SHEET (RULE 26) pumping a drilling fluid into an earth formation, as shown at act 202. The drilling fluid may include one or more of the drilling fluids described above and may include one or more of the viscosifiers described above.

[0055] The method 200 may further include drilling the earth formation while pumping the drilling fluid into the earth formation, as shown at act 204. In some embodiments, the drilling fluid is circulated through the drill string, out of the drill bit, and through the annulus between the drill string and the earth formation. The drilling fluid may facilitate removal of cuttings from the wellbore as the drilling fluid circulates through the wellbore. [0056] In some embodiments, a filtercake is formed on surfaces of the earth formation defining the wellbore. The filtercake may include the viscosifier and may include, for example, crosslinked polymers formed from one or more monomers and crosslinked with one or more of the crosslinkers described above, the crosslinkers including one or more ether groups.

[0057] The method 200 may further include circulating a breaker fluid to break a filtercake, as shown in act 206. The breaker fluid may include any of the breaker fluids previously described. Responsive to exposure to the breaker fluid, ether groups of the viscosifier (e.g., in the filtercake) may hydrolyze to break the filtercake, facilitating removal of the filtercake from the earth formation.

[0058] The viscosifiers described herein may be suitable for use in HTHP wellbores. Since the viscosifier includes one or more ether groups in the crosslinker, the viscosifier may be broken after drilling operations are complete and prior to completion operations. Advantageously, the viscosifier is suitable for HTHP conditions, but is also easily broken responsive to exposure to the breaker fluid.

[0059] The embodiments of drilling fluids, the viscosifiers, and the crosslinkers have been primarily described with reference to wellbore drilling operations; the drilling fluids, viscosifiers, and crosslinkers described herein may be used in applications other than the drilling of a wellbore. In other embodiments, drilling fluids, viscosifiers, and crosslinkers according to the present disclosure may be used outside a wellbore or other downhole environment used for the exploration or production of natural resources. For instance, drilling fluids, viscosifiers, and crosslinkers of the present disclosure may be used in a borehole used for placement of utility lines. Accordingly, the terms “wellbore,” “borehole”

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SUBSTITUTE SHEET (RULE 26) and the like should not be interpreted to limit tools, systems, assemblies, or methods of the present disclosure to any particular industry, field, or environment.

[0060] One or more specific embodiments of the present disclosure are described herein. These described embodiments are examples of the presently disclosed techniques. Additionally, in an effort to provide a concise description of these embodiments, not all features of an actual embodiment may be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous embodiment-specific decisions will be made to achieve the developers’ specific goals, such as compliance with system -related and business-related constraints, which may vary from one embodiment to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0061] Additionally, it should be understood that references to “one embodiment” or “an embodiment” of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. For example, any element described in relation to an embodiment herein may be combinable with any element of any other embodiment described herein. Numbers, percentages, ratios, or other values stated herein are intended to include that value, and also other values that are “about” or “approximately” the stated value, as would be appreciated by one of ordinary skill in the art encompassed by embodiments of the present disclosure. A stated value should therefore be interpreted broadly enough to encompass values that are at least close enough to the stated value to perform a desired function or achieve a desired result. The stated values include at least the variation to be expected in a suitable manufacturing or production process, and may include values that are within 5%, within 1%, within 0.1%, or within 0.01% of a stated value.

[0062] A person having ordinary skill in the art should realize in view of the present disclosure that equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations may be made to embodiments disclosed herein without departing from the spirit and scope of the present disclosure. Equivalent constructions, including functional “means-plus-function” clauses

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SUBSTITUTE SHEET (RULE 26) are intended to cover the structures described herein as performing the recited function, including both structural equivalents that operate in the same manner, and equivalent structures that provide the same function. It is the express intention of the applicant not to invoke means-plus-function or other functional claiming for any claim except for those in which the words ‘means for’ appear together with an associated function. Each addition, deletion, and modification to the embodiments that falls within the meaning and scope of the claims is to be embraced by the claims.

[0063] The terms “approximately,” “about,” and “substantially” as used herein represent an amount close to the stated amount that is within standard manufacturing or process tolerances, or which still performs a desired function or achieves a desired result. For example, the terms “approximately,” “about,” and “substantially” may refer to an amount that is within less than 5% of, within less than 1% of, within less than 0.1% of, and within less than 0.01% of a stated amount. Further, it should be understood that any directions or reference frames in the preceding description are merely relative directions or movements. For example, any references to “up” and “down” or “above” or “below” are merely descriptive of the relative position or movement of the related elements.

[0064] The present disclosure may be embodied in other specific forms without departing from its spirit or characteristics. The described embodiments are to be considered as illustrative and not restrictive. The scope of the disclosure is, therefore, indicated by the appended claims rather than by the foregoing description. Changes that come within the meaning and range of equivalency of the claims are to be embraced within their scope.

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SUBSTITUTE SHEET (RULE 26)

Claims

What is claimed is:

1. A drilling fluid, comprising: water; and a viscosifier comprising a crosslinked polymer comprising: a polymer formed from one or more monomers; and a crosslinker comprising a reaction product of a first reactant comprising a linear amine and a second reactant comprising one of: an ether comprising an epoxide group; and allyl chloride.

2. The drilling fluid of claim 1, further comprising at least one salt dispersed in the water.

3. The drilling fluid of claim 1, wherein the crosslinker comprises a reaction product of ethylene diamine and allyl diglycidyl ether.

4. The drilling fluid of claim 3, wherein a molar ratio of the ethylene diamine to the allyl diglycidyl ether is about 1.0:4.0.

5. The drilling fluid of claim 1, wherein the crosslinker comprises between 1 ether linkage and 4 ether linkages.

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SUBSTITUTE SHEET (RULE 26)

6. The drilling fluid of claim 1, wherein the one or more monomers are selected from the group consisting of one or more of acrylamide, methacrylamide, an N- substituted acrylamide, an N-N-dimethylacrylamide, an N-substituted methacrylamide, an acrylate, a metacrylate, acrylic acid, methacrylic acid, an N- vinylamide, an N-allyl amide, vinyl alcohol, a vinyl ether, a vinyl ester, an allyl alcohol, an allyl ether, an allyl ester, an acrylic ester, a methacrylic ester, N- vinylformamide, N-vinyl acetamide, N-vinylpyridine, N-vinylpyrrolidone, a sulfonated anionic monomer, allyl sulfonates, vinylimidazole, allylimidazole, and diallyldimethylammonium chloride.

7. The drilling fluid of claim 1, wherein the linear amine comprises a diamine.

8. The drilling fluid of claim 1, wherein the linear amine comprises at least one terminal amine group.

9. The drilling fluid of claim 1, wherein the ether comprises three ether groups.

10. The drilling fluid of claim 1, wherein the ether comprises glycerol triglycidyl ether.

11. The drilling fluid of claim 1, wherein the linear amine comprises diallyl amine.

12. The drilling fluid of claim 1, wherein the one or more monomers comprises at least one acrylamide monomer and at least one sulfonated anionic monomer.

13. The drilling fluid of claim 1, wherein the crosslinker comprises the following structure:

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SUBSTITUTE SHEET (RULE 26)

4. The drilling fluid of claim 1, wherein the crosslinker comprises the following structure:

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SUBSTITUTE SHEET (RULE 26)

15. The drilling fluid of claim 1, wherein the crosslinker comprises the following structure:

16. A method of operating a wellbore, the method comprising: pumping a wellbore fluid into a wellbore through an earth formation, the wellbore fluid comprising:

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SUBSTITUTE SHEET (RULE 26) a base fluid; and a crosslinked polymer comprising: at least one monomeric unit; and a crosslinker comprising a reaction product of a linear amine and at least one of allyl glycidyl ether, glycerol triglycidyl ether, and allyl chloride; and operating a drill bit while pumping the wellbore fluid in the wellbore.

17. The method of claim 16, further comprising forming a filtercake on walls of the earth formation while operating the drill bit.

18. The method of claim 17, further comprising, after drilling the wellbore, breaking the filtercake by reacting an ether group of the filtercake with an acid or an oxidizer.

19. The method of claim 16, wherein pumping a wellbore fluid through an earth formation comprising pumping a wellbore fluid comprising a viscosifier including a crosslinker comprising a reaction product of ethylene diamine and allyl glycidyl ether into the earth formation.

20. A drilling fluid, comprising: a base fluid comprising water; and a viscosifier comprising a reaction product of: at least one monomeric unit; and a crosslinker comprising: a first reactant selected from the group consisting of ethylene diamine, diallyl amine, and 2,2-oxybis[N-methylethanamine]; and a second reactant selected from the group consisting of allyl glycidyl ether, glycerol triglycidyl ether, and allyl chloride.

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SUBSTITUTE SHEET (RULE 26)