CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation-in-part of U .S. patent application Ser. No. 12/046,086, now published as 2008/0224087, entitled "Improved Aqueous-Based Insulating Fluids and Related Methods," filed on Mar. 11, 2008, which is a continuation-in-part of U .S. patent application Ser. No. 11/685,909, now published as 2008/0227665, entitled "Improved Aqueous- Based Insulating Fluids and Related Methods," filed on Mar. 14, 2007, the entirety of each of these is incorporated herein by reference, and from which priority is claimed pursuant to 35 U .S.C. § 120.

BACKGROUND

[0002] The present invention relates to insulating fluids, and more particularly, to aqueous-based insulating fluids that have greater stability at high temperatures with lower thermal conductivity that may be used, for example, in applications requiring an insulating fluid such as pipeline and subterranean applications (e.g. , to insulate petroleum production conduits) .

[0003] Insulating fluids are often used in subterranean operations wherein the fluid is placed into an annulus between a first tubing and a second tubing or the walls of a well bore. The insulating fluid acts to insulate a first fluid (e.g. , a hydrocarbon fluid) that may be located within the first tubing from the environment surrounding the first tubing or the second tubing to enable optimum recovery of the hydrocarbon fluid . For instance, if the surrounding environment is very cold, the insulating fluid is thought to protect the first fluid in the first tubing from the environment so that it can efficiently flow through the production tubing, e.g. , the first tubing, to other facilities. This is desirable because heat transfer can cause problems such as the precipitation of heavier hydrocarbons, severe reductions in flow rate and, in some cases, casing collapse. Additionally, when used in packer applications, a required amount of hydrostatic head pressure is needed . Thus, higher density insulating fluids are often used for this reason as well to provide the requisite hydrostatic force.

[0004] Such fluids also may be used for similar applications involving pipelines for similar purposes, e.g. , to protect a fluid located within the pipeline from the surrounding environmental conditions so that the fluid can efficiently flow through the pipeline. Insulating fluids can be used in other insulating applications as well wherein it is desirable to control heat transfer. These applications may or may not involve hydrocarbons.

[0005] Beneficial insulating fluids preferably have a low inherent thermal conductivity, and also should remain gelled to prevent, inter alia, convection currents that could carry heat away. Additionally, preferred insulating fluids should be aqueous-based, and easy to handle and use. Moreover, preferred fluids should tolerate ultra high temperatures (e.g. , temperatures of 400°F or above) for long periods of time for optimum performance.

[0006] Conventional aqueous-based insulating fluids have many drawbacks. First, many have associated temperature limitations. Typically, most aqueous-based insulating fluids are only stable up to 240°F for relatively short periods of time. This can be problematic because it can result in premature degradation of the fluid, which can cause the fluid not to perform its desired function with respect to insulating the first fluid. A second common limitation of many conventional aqueous-based insulating fluids is their density range. Typically, these fluids have an upper density limit of 12.5 ppg. Oftentimes, higher densities are desirable to maintain adequate pressure for the chosen application . Additionally, most aqueous-based insulating fluids have excessive thermal conductivities, which means that these fluids are not as efficient or effective at controlling conductive heat transfer. Moreover, when a viscosified fluid is required to eliminate convective currents, oftentimes to obtain the required viscosity in current aqueous-based fluids, the fluids may become too thick to be able to pump into place. Some aqueous-based fluids also can have different salt tolerances that may not be compatible with various brines used, which limits the operators' options as to what fluids to use in certain circumstances.

[0007] In some instances, insulating fluids may be oil-based . Certain oil-based fluids may offer an advantage because they may have lower thermal conductivity as compared to their aqueous counterparts. However, many disadvantages are associated with these fluids as well . First, oil-based insulating fluids can be hard to "weight up," meaning that it may be hard to obtain the necessary density required for an application. Secondly, oil-based fluids may present toxicity and other environmental issues that should be managed, especially when such fluids are used in sub-sea applications. Additionally, there can be interface issues if aqueous completion fluids are used. Another complication presented when using oil-based insulating fluids is the concern about their compatibility with any elastomeric seals that may be present along the first tubing line.

[0008] Another method that may be employed to insulate a first tubing involves using vacuum insulated tubing. However, this method also can present disadvantages. First, when the vacuum tubing is installed on a completion string, sections of the vacuum tubing can fail. This can be a costly problem involving a lot of down time. In severe cases, the first tubing can collapse. Secondly, vacuum insulated tubing can be very costly and hard to place. Moreover, in many instances, heat transfer at the junctions or connective joints in the vacuum tubings can be problematic. These may lead to "hot spots" in the tubings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following figures are included to illustrate certain aspects of the present invention, and should not be viewed as exclusive embodiments. The subject matter disclosed is capable of considerable modifications, alterations, combinations, and equivalents in form and function, as will occur to those skilled in the art and having the benefit of this disclosure.

[0010] FIG. 1 lists the materials used in the formulations and the amounts thereof as described in Example 1 in the Examples section.

[0011] FIG. 2 illustrates data from a fluid that was heated to about 190°F for 5000 minutes to activate the crosslinking agent and provide an increase in viscosity.

[0012] FIG. 3 lists the materials that may be used in the formulations and the approximate amounts thereof as described in Example 2 in the Examples section.

[0013] FIG. 4 illustrates data from a fluid that was heated from approximately 100°F to approximately 600°F for approximately 45,000 seconds at approximately 10,000 psi.

[0014] FIG. 5 provides a photograph of various insulating fluids subjected to long-term, high-temperature conditions. DETAILED DESCRIPTION

[0015] The present invention relates to insulating fluids, and more particularly, to aqueous-based insulating fluids that have greater stability at high temperatures with lower thermal conductivity that may be used, for example, in applications requiring an insulating fluid such as pipeline and subterranean applications (e.g., to insulate petroleum production conduits) . The aqueous- based insulating fluids of the present invention may be used in any application requiring an insulating fluid . Preferably, they may have particular use in pipeline and subterranean applications.

[0016] The improved aqueous-based insulating fluids and methods of the present invention have many potential advantages. One of these many advantages is that the fluids, in some embodiments, may have enhanced thermal stability, which enables them to be beneficially used in many applications. Secondly, in some embodiments, the aqueous-based insulating fluids of the present invention may have higher densities than conventional aqueous-based insulating fluids, and therefore, present a distinct advantage in that respect. Additionally, the aqueous-based insulating fluids of the present invention may have relatively low thermal conductivity, which is thought to be especially beneficial in certain applications. In some embodiments, these fluids are believed to be very durable. Moreover, in some embodiments, the fluids of the present invention offer aqueous-based viscous insulating fluids with a broad fluid density range, decreased thermal conductivity, and stable gel properties at temperatures exceeding those of current industry standards (e.g. , even at temperatures of about 600°F or more, depending on the organic liquid included) . Another potential advantage is that these fluids may prevent the formation of hydrates within the insulating fluids themselves or the fluids being insulated . Other advantages and objects of the invention may be apparent to one skilled in the art with the benefit of this disclosure.

[0017] In certain embodiments, the aqueous-based insulating fluids of the present invention comprise an aqueous base fluid, a water-miscible organic liquid, and a layered silicate. In certain embodiments, the aqueous-based insulating fluids of the present invention comprise an aqueous base fluid, a water-miscible organic liquid, a layered silicate, and optionally a synthetic polymer. In some instances, the polymer may be crosslinked by using or adding to the fluid an appropriate crosslinking agent. Thus, the term "polymer" as used herein refers to oligomers, homopolymers, copolymers, terpolymers and the like, which may or may not be crosslinked . Optionally, the aqueous-based insulating fluids of the present invention may comprise other additives such as corrosion inhibitors, pH modifiers, biocides, glass beads, hollow spheres (e.g. , hollow microspheres), rheology modifiers, buffers, hydrate inhibitors, breakers, tracers, additional weighting agents, viscosifiers, surfactants, and combinations of any of these. Other additives may be appropriate as well and beneficially used in conjunction with the aqueous-based insulating fluids of the present invention as may be recognized by one skilled in the art with the benefit of this disclosure.

[0018] The aqueous base fluids that may be used in the aqueous-based insulating fluids of the present invention include any aqueous fluid suitable for use in insulating, subterranean, or pipeline applications. In some instances, brines may be used, for example, when a relatively denser aqueous-based insulating fluid is desired (e.g. , density of 10.5 ppg or greater); however, it may be observed that the fluids of the present invention may be less tolerant to higher concentrations of salts than other fluids, such as those that include a polymer, but not a layered silicate as described herein . Suitable brines include, but are not limited to those that contain : NaCI, Na Br, KCI, CaCI ₂ , Ca Br ₂ , ZrBr ₂ , sodium carbonate, sodium formate, potassium formate, cesium formate, and combinations and derivatives of these brines. Others may be appropriate as well . The specific brine used may be dictated by the desired density of the resulting aqueous-based insulating fluid or for compatibility with other completion fluid brines that may be present. Denser brines may be useful in some instances. A density that is suitable for the application at issue should be used as recognized by one skilled in the art with the benefit of this disclosure. When deciding how much of an aqueous fluid to include, a general guideline to follow is that the aqueous fluid component should comprise the balance of a high temperature aqueous-based insulating fluid after considering the amount of the other components present therein .

[0019] The water-miscible organic liquids that may be included in the aqueous-based insulating fluids of the present invention include water-miscible materials having relatively low thermal conductivity (e.g. , about half as conductive as water or less) . By "water-miscible," it is meant that about 5 grams or more of the organic liquid will disperse in 100 grams of water. Suitable water- miscible organic liquids include, but are not limited to, esters, amines, alcohols, polyols, glycol ethers, or combinations and derivatives of these. Examples of suitable esters include low molecular weight esters; specific examples include, but are not limited to, methylformate, methyl acetate, and ethyl acetate. Combinations and derivatives are also suitable. Examples of suitable amines include low molecular weight amines; specific examples include, but are not limited to, diethyl amine, 2-aminoethanol, and 2-(dimethylamino)ethanol . Combinations and derivatives are also suitable. Examples of suitable alcohols include methanol, ethanol, propanol, isopropanol, and the like. Combinations and derivatives are also suitable. Examples of glycol ethers include ethylene glycol butyl ether, diethylene glycol methyl ether, dipropylene glycol methyl ether, tripropylene glycol methyl ether, and the like. Combinations and derivatives are also suitable. Of these, polyols are generally preferred in most cases over the other liquids since they generally are thought to exhibit greater thermal and chemical stability, higher flash point values, and are more benign with respect to elastomeric materials.

[0020] Suitable polyols are those aliphatic alcohols containing two or more hydroxy groups. It is preferred that the polyol be at least partially water- miscible. Examples of suitable polyols that may be used in the aqueous-based insulating fluids of this invention include, but are not limited to, watersoluble diols such as ethylene glycols, propylene glycols, polyethylene glycols, polypropylene glycols, diethylene glycols, triethylene glycols, dipropylene glycols and tripropylene glycols, combinations of these glycols, their derivatives, and reaction products formed by reacting ethylene and propylene oxide or polyethylene glycols and polypropylene glycols with active hydrogen base compounds {e.g. , polyalcohols, polycarboxylic acids, polyamines, or polyphenols). The polyglycols of ethylene generally are thought to be water miscible at molecular weights at least as high as 20,000. The polyglycols of propylene, although giving slightly better grinding efficiency than the ethylene glycols, are thought to be water-miscible up to molecular weights of only about 1,000. Other glycols possibly contemplated include neopentyl glycol, pentanediols, butanediols, and such unsaturated diols as butyne diols and butene diols. In addition to the diols, the triol, glycerol, and such derivatives as ethylene or propylene oxide adducts may be used . Other higher polyols may include pentaerythritol. Another class of polyhydroxy alcohols contemplated is the sugar alcohols. The sugar alcohols are obtained by reduction of carbohydrates and differ greatly from the above-mentioned polyols. Combinations and derivatives of these are suitable as well .

[0021] The choice of polyol to be used is largely dependent on the desired density of the fluid . Other factors to consider include thermal conductivity. For higher density fluids (e.g. , 10.5 ppg or higher), a higher density polyol may be preferred, for instance, triethylene glycol or glycerol may be desirable in some instances. For lower density applications, ethylene or propylene glycol may be used. In some instances, more salt may be necessary to adequately weight the fluid to the desired density. In certain embodiments, the amount of polyol that should be used may be governed by the thermal conductivity ceiling of the fluid and the desired density of the fluid . If the thermal conductivity ceiling is 0.17 BTU/hft°F, then the concentration of the polyol may be about 40% to about 99% of a high temperature aqueous-based insulating fluid of the present invention. A more preferred range could be about 70% to about 99%.

[0022] Examples of layered silicates that may be suitable for use in the present invention include, but are not limited to, smectite, vermiculite, swellable fluoromica, montmorillonite, beidellite, hectorite, and saponite. A high- temperature, electrolyte stable synthetic hectorite may be particularly useful in some embodiments. An example of a synthetic hectorite clay for use in accordance with this invention is LAPONITE® RD (commercially available from Laporte Absorbents Company of Cheshire, United Kingdom). Mixtures of any of these of silicates may be suitable as well. In preferred embodiments, the silicate may be at least partially water soluble. In some embodiments, the layered silicate may be a natural layered silicate or a synthetic layered silicate. In certain embodiments, the silicate should comprise about 0.1% to about 15% weight by volume of the fluid, and more preferably, about 0.5% to about 4% weight by volume of the fluid .

[0023] Inclusion of a synthetic polymer may be useful, inter alia, to produce fluids that exhibit gelation behavior. Examples of synthetic polymers that optionally may be suitable for use in the present invention include, but are not limited to, acrylic acid polymers, acrylic acid ester polymers, acrylic acid derivative polymers, acrylic acid homopolymers, acrylic acid ester homopolymers (such as poly(methyl acrylate), poly (butyl acrylate), and poly(2-ethylhexyl acrylate)), acrylic acid ester co-polymers, methacrylic acid derivative polymers, methacrylic acid homopolymers, methacrylic acid ester homopolymers (such as poly(methyl methacrylate), polyacrylamide homopolymer, n-vinyl pyrrolidone and polyacrylamide copolymers, poly(butyl methacrylate), and poly (2- ethylhexyl methacrylate)), n-vinyl pyrrolidone, acrylamido-methyl-propane sulfonate polymers, acrylamidomethyl-propane sulfonate derivative polymers, acrylamidomethyl-propane sulfonate co-polymers, and acrylic acidlacrylamido- methyl-propane sulfonate copolymers, and combinations thereof. Copolymers and terpolymers may be suitable as well . Mixtures of any of these of polymers may be suitable as well . In preferred embodiments, the polymer should be at least partially water soluble. Suitable polymers can be cationic, anionic, nonionic, or zwitterionic. In certain embodiments, the polymer should comprise about 0.1% to about 15% weight by volume of the fluid, and more preferably, about 0.5% to about 4%.

[0024] To obtain the desired gel characteristics and thermal stability for an aqueous-based insulating fluid of the present invention, the polymer included in the fluid may be crosslinked by an appropriate crosslinking agent. In those embodiments of the present invention wherein it is desirable to crosslink the polymer, optionally and preferably, one or more crosslinking agents may be added to the fluid to crosslink the polymer.

[0025] One type of suitable crosslinking agent is a combination of a phenolic component (or a phenolic precursor) and formaldehyde (or a formaldehyde precursor) . Suitable phenolic components or phenolic precursors include, but are not limited to, phenols, hydroquinone, salicylic acid, salicylamide, aspirin, methyl-p-hydroxybenzoate, phenyl acetate, phenyl salicylate, o-aminobenzoic acid, p-aminobenzoic acid, m-aminophenol, furfuryl alcohol, and benzoic acid . Suitable formaldehyde precursors may include, but are not limited to, hexamethylenetetramine, glyoxal, and 1,3,5-trioxane. This crosslinking agent system needs approximately 250°F to thermally activate to crosslink the polymer. Another type of suitable crosslinking agent is polyalkylimine. This crosslinking agent needs approximately 90°F to activate to crosslink the polymer. This crosslinking agent may be used alone or in conjunction with any of the other crosslinking agents discussed herein .

[0026] Another type of crosslinking agent that may be used includes non-toxic organic crosslinking agents that are free from metal ions. Examples of such organic cross-linking agents are polyalkyleneimines (e.g. , polyethyleneimine), polyalkylenepolyamines and mixtures thereof. In addition, water-soluble polyfunctional aliphatic amines, arylalkylamines and heteroarylalkylamines may be utilized .

[0027] When included, suitable crosslinking agents may be present in the fluids of the present invention in an amount sufficient to provide, inter alia, the desired degree of crosslinking . In certain embodiments, the crosslinking agent or agents may be present in the fluids of the present invention in an amount in the range of about 0.0005% to about 10% weight by volume of the fluid . In certain embodiments, the crosslinking agent may be present in the fluids of the present invention in an amount in the range of about 0.001% to about 5% weight by volume of the fluid . One of ordinary skill in the art, with the benefit of this disclosure, will recognize the appropriate amount of crosslinking agent to include in a fluid of the present invention based on, among other things, the temperature conditions of a particular application, the type of polymer(s) used, the molecular weight of the polymer(s), the desired degree of viscosification, and/or the pH of the fluid.

[0028] Although any suitable method for forming the insulating fluids of the present invention may be used, in some embodiments, an aqueous-based insulating fluid of the present invention may be formulated at ambient temperature and pressure conditions by mixing water and a chosen water- miscible organic liquid . The water and water-miscible organic liquid preferably may be mixed so that the water-miscible organic liquid is miscible in the water. The chosen silicate may then be added and mixed into the water and water- miscible organic liquid mixture until the silicate is hydrated . Any chosen additives may be added at any point, including a polymer. Preferably, any additives are dispersed within the mixture. If desired, a crosslinking agent may be added. If used, it should be dispersed in the mixture. Crosslinking, however, generally should not take place until thermal activation, which preferably, in subterranean applications, occurs downhole; this may alleviate any pumping difficulties that might arise as a result of activation before placement. Activation results in the fluid forming a gel . The term "gel," as used herein, and its derivatives refer to a semi-solid, jelly-like state assumed by some colloidal dispersions. Once activated, the gel should stay in place and be durable with negligible syneresis. [0029] In some embodiments, the gels formed by hydrating the silicate may have a zero sheer viscosity of about 100,000 centipoise measured on an Anton Paar Controlled Stress Rheometer at standard conditions using standard operating procedures.

[0030] Once gelled, if the fluid contains polymer, one method of minimizing or removing the gel may comprise diluting or breaking the crosslinks and/or the polymer structure within the gel using an appropriate method and/or composition to allow recovery or removal of the gel. Another method could involve physical removal of the gel by, for example, air or liquid.

[0031] In some embodiments, the aqueous-based insulating fluids of the present invention may be prepared on-the-fly at a well-site or pipeline location. In other embodiments, the aqueous-based insulating fluids of the present invention may be prepared off-site and transported to the site of use. In transporting the fluids, one should be mindful of the activation temperature of the fluid .

[0032] In one embodiment, the present invention provides a method comprising : providing a first tubing; providing a second tubing that substantially surrounds the first tubing thus creating an annulus between the first tubing and the second tubing; providing an aqueous-based insulating fluid that comprises an aqueous base fluid, a polyol, and a layered silicate; and placing the aqueous- based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid also includes a polymer. The tubings may have any shape appropriate for a chosen application. In some instances, the second tubing may not be the same length as the first tubing. In some instances, the tubing may comprise a portion of a larger apparatus. In some instances, the aqueous-based insulating fluid may be in contact with the entire first tubing from end to end, but in other situations, the aqueous-based insulating fluid may only be placed in a portion of the annulus and thus only contact a portion of the first tubing. In some instances, the first tubing may be production tubing located within a well bore. In some instances, the tubings may be located in a geothermal well bore. The production tubing may be located in an off-shore location. In other instances, the production tubing may be located in a cold climate. In other instances, the first tubing may be a pipeline capable of transporting a fluid from one location to a second location. [0033] In one embodiment, the present invention provides a method comprising : providing a first tubing; providing a second tubing that substantially surrounds the first tubing thus creating an annulus between the first tubing and the second tubing; providing an aqueous-based insulating fluid that comprises an aqueous base fluid, a water-miscible organic liquid, and a layered silicate; and placing the aqueous-based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid also includes a polymer.

[0034] In one embodiment, the present invention provides a method comprising : providing a tubing containing a first fluid located within a well bore such that an annulus is formed between the tubing and a surface of the well bore; providing an aqueous-based insulating fluid that comprises an aqueous base fluid, a water-miscible organic liquid, and a layered silicate; and placing the aqueous-based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid also includes a polymer.

[0035] In one embodiment, the present invention provides a method comprising : providing a first tubing that comprises at least a portion of a pipeline that contains a first fluid; providing a second tubing that substantially surrounds the first tubing thus creating an annulus between the first tubing and the second tubing; providing an aqueous-based insulating fluid that comprises an aqueous base fluid, a water-miscible organic liquid, and a layered silicate; and placing the aqueous-based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid also includes a polymer.

[0036] In one embodiment, the present invention provides an aqueous- based insulating fluid that comprises an aqueous base fluid, a water-miscible organic liquid, and a layered silicate. In some embodiments, the aqueous-based insulating fluid also includes a polymer.

[0037] In another embodiment, the present invention provides a method of forming an aqueous-based insulating fluid comprising : mixing an aqueous base fluid and a water-miscible organic liquid to form a mixture; adding at least one layered silicate to the mixture; allowing the layered silicate to hydrate; placing the mixture comprising the layered silicate in a chosen location; and allowing the mixture comprising the layered silicate to activate to form a gel therein. In some embodiments, a polymer may be added to the mixture and allowed to hydrate. Optionally, a crosslinking agent may be added to the mixture comprising the polymer to crosslink the polymer. [0038] In some embodiments, an aqueous-based insulating fluid described herein may advantageously be utilized in subsea applications, e.g. , to mitigate thickening of fluids flowing through a riser. In subsea applications, the subterranean formation temperature is often significantly higher than that of the ocean, especially in deep-water. Treatment fluids, e.g., drilling fluids, are often designed to have specific rheological properties at the temperatures of the subterranean formation. However, in subsea applications, the reduced temperature of the ocean disposed about the riser causes the treatment fluid to have different rheological properties in the riser portion then in the wellbore portion. Accordingly, many subterranean operations that are highly dependent on the rheological properties of treatment fluids are unavailable or very costly to be performed in subsea applications, e.g. , managed pressure drilling operations and dual gradient operations. Further, the rheological changes along the wellbore increase the risk of damage to the formation or wellbore tools (e.g. , the riser or a blowout preventer), which can be reduced with the use of high-stability insulating fluids.

[0039] The aqueous-based insulating fluids described herein may advantageously be utilized, in some embodiments, in an annulus disposed about the riser to mitigate fluid temperature reduction associated with flowing through the riser. Surprisingly, it has been observed that fluids passing through a riser insulated with the aqueous-based insulating fluid described herein are about 20% to about 40% warmer than without the insulting fluid. As such, the rheological properties of the fluids are better controlled (e.g. , mitigating yield point increases and minimizing the plastic viscosity of the fluid), which in turn reduces the risk of pressure spikes and lowers the equivalent circulating density ("ECD") of the fluid . A lower ECD allows for a flatter rheological profile in a narrow pore pressure-fracture pressure gradient window, thereby mitigating formation damage during managed pressure drilling operations.

[0040] Further, the aqueous-based insulating fluids described herein are more stable than crosslinked biopolymer systems, thereby reducing the frequency with which an insulating fluid would need to be replace. In some instances, at least a portion of the aqueous-based insulating fluid may exposed to a temperature of about 30°F to about 400°F for 30 days or greater without significant reduction in performance (e.g. , thermal conductivity). In some instances, at least a portion of the aqueous-based insulating fluid may be exposed to a temperature of about 250°F to about 400°F for 30 days or greater without significant reduction in performance.

[0041] In some embodiments, the present invention provides a method comprising : providing an aqueous-based insulating fluid in an annulus between a riser column and an outer casing disposed thereabout, the riser column connecting a wellbore penetrating a subterranean formation to a floating surface rig ; and flowing a fluid through the riser column and the wellbore. In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, and a synthetic polymer crosslinked with a crosslinker. In some embodiments, providing the aqueous-based insulating fluid in the annulus may involve placing the aqueous-based fluid in the annulus, the aqueous-based fluid comprising an aqueous base fluid, a water miscible organic liquid, a synthetic polymer, and a crosslinker; and crosslinking the synthetic polymer with the crosslinker. In some instances, crosslinking may involve exposing the aqueous-based insulating fluid to a temperature of about 90°F or greater, which may occur before, after, or during placing the aqueous- based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, a layered silicate, and optionally a synthetic polymer, which may optionally be crosslinked (e.g. , via the crosslinking described above) .

[0042] In some instances, the fluid passing through the riser may be a drilling fluid, a formation fluid, or the like. In some embodiments, methods may further involve performing a managed pressure drilling operation to extend the wellbore in the subterranean formation . In other embodiments, methods may further involve performing a dual gradient drilling operation to extend the wellbore in the subterranean formation .

[0043] In some instances, the aqueous-based insulating fluids described herein may be utilized in conjunction with formations having variable temperatures along the length of a wellbore, especially in formations where near the surface the formation comprises permafrost. Formations comprising permafrost are prone to wellbore collapse when the fluids flowing therethrough are sufficient to melt the permafrost. Further, the geographical locations where formations comprising permafrost are located may have additional environmental concerns and regulations. The ability to minimize the local temperature changes for mitigating permafrost melting may be advantageous in such locations.

[0044] Some embodiments of the present invention may involve providing an aqueous-based insulating fluid in an annulus between a tubing and an outer casing disposed thereabout; and flowing a fluid at about 40°F or greater (e.g. , about 40°F to about 110°F) through the tubing . In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, and a synthetic polymer crosslinked with a crosslinker. In some embodiments, providing the aqueous-based insulating fluid in the annulus may involve placing the aqueous-based fluid in the annulus, the aqueous-based fluid comprising an aqueous base fluid, a water miscible organic liquid, a synthetic polymer, and a crosslinker; and crosslinking the synthetic polymer with the crosslinker. In some instances, crosslinking may involve exposing the aqueous-based insulating fluid to a temperature of about 90°F or greater, which may occur before, after, or during placing the aqueous- based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, a layered silicate, and optionally a synthetic polymer, which may optionally be crosslinked (e.g. , via the crosslinking described above) .

[0045] In some instances, the fluid may be a drilling fluid, a formation fluid, or the like. In some embodiments, methods may further involve producing hydrocarbons from the subterranean formation .

[0046] In some embodiments, the aqueous-based insulating fluids described herein may be used in conjunction with other high-temperature fluids, e.g., geothermal wells or steam injection wells. The aqueous-based insulating fluids may advantageously mitigate column expansion while enhancing the efficiency of the wellbore operation because reduced heat loss of the high- temperature fluid flowing therethrough . Column expansion can lead to formation damage, column failure, and wellbore collapse. Because of the high temperatures in steam injection wells, crosslinked biopolymer systems tend to degrade and lose insulating efficacy rapidly. The high-temperature stability of the aqueous-based insulating fluids described herein (e.g., greater than about 300°F or, in some instances, as high as 600°F) may advantageously mitigate the frequency with which insulating fluids need to be replaced . [0047] Some embodiments of the present invention may involve providing an aqueous-based insulating fluid in an annulus between a tubing and a casing string (e.g., a wellbore liner, a cement casing, or the like), the aqueous-based insulating fluid comprising an aqueous base fluid, a water- miscible organic liquid, and a synthetic polymer crosslinked with a crosslinker; and flowing a fluid at a temperature greater than about 225°F through the tubing and into the subterranean formation . In some instances, the fluid temperature may be from about 250°F to about 600°F, depending on the application .

[0048] Some embodiments of the present invention may involve providing an aqueous-based insulating fluid in an annulus between a tubing and a casing disposed thereabout; and flowing steam through the tubing and into the subterranean formation . In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, and a synthetic polymer crosslinked with a crosslinker. In some embodiments, providing the aqueous-based insulating fluid in the annulus may involve placing the aqueous-based fluid in the annulus, the aqueous-based fluid comprising an aqueous base fluid, a water miscible organic liquid, a synthetic polymer, and a crosslinker; and crosslinking the synthetic polymer with the crosslinker. In some instances, crosslinking may involve exposing the aqueous-based insulating fluid to a temperature of about 90°F or greater, which may occur before, after, or during placing the aqueous-based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, a layered silicate, and optionally a synthetic polymer, which may optionally be crosslinked (e.g., via the crosslinking described above) . Some embodiments may further involve producing hydrocarbons from the subterranean formation .

[0049] In some instances, the aqueous-based insulating fluid may be utilized in the production well corresponding to a steam well . Generally, the steam well is utilized for injecting steam, which heats the heavy oil and reduces the viscosity. By utilizing aqueous-based insulating fluids described herein in the production wells, the heavy oil may advantageously retain the heat from the steam and flow through the production well more easily and with less energy input (e.g., lower pumping pressures). [0050] Some embodiments of the present invention may involve providing an aqueous-based insulating fluid in an annulus between a tubing and a casing disposed thereabout within a production wellbore; injecting steam into a subterranean formation comprising heavy oil so as to yield heated heavy oil ; and producing the heated heavy oil via the production wellbore. In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, and a synthetic polymer crosslinked with a crosslinker. In some embodiments, providing the aqueous-based insulating fluid in the annulus may involve placing the aqueous-based fluid in the annulus, the aqueous-based fluid comprising an aqueous base fluid, a water- miscible organic liquid, a synthetic polymer, and a crosslinker; and crosslinking the synthetic polymer with the crosslinker. In some instances, crosslinking may involve exposing the aqueous-based insulating fluid to a temperature of about 90°F or greater, which may occur before, after, or during placing the aqueous- based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, a layered silicate, and optionally a synthetic polymer, which may optionally be crosslinked (e.g. , via the crosslinking described above) .

[0051] In some instances, the aqueous-based fluids described herein may be used to prevent damage to cemented casings. Cement casings are prone to cracking, degrading, forming microannuli, and the like with thermal fluctuation that are often a consequence of performing a plurality of wellbore operations. Such degradation, e.g. , especially microannuli, inhibit zonal isolation and well control, which, in some instances, can lead to wellbore blowouts, contamination of isolated water tables, and the like.

[0052] Some embodiments of the present invention may involve providing an aqueous-based insulating fluid in an annulus between a pipe (or liner or the like) and a cement casing disposed thereabout; and flowing a fluid through the pipe. In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, and a synthetic polymer crosslinked with a crosslinker. In some embodiments, providing the aqueous-based insulating fluid in the annulus may involve placing the aqueous- based fluid in the annulus, the aqueous-based fluid comprising an aqueous base fluid, a water miscible organic liquid, a synthetic polymer, and a crosslinker; and crosslinking the synthetic polymer with the crosslinker. In some instances, crosslinking may involve exposing the aqueous-based insulating fluid to a temperature of about 90°F or greater, which may occur before, after, or during placing the aqueous-based insulating fluid in the annulus. In some embodiments, the aqueous-based insulating fluid may comprise an aqueous base fluid, a water-miscible organic liquid, a layered silicate, and optionally a synthetic polymer, which may optionally be crosslinked (e.g., via the crosslinking described above) .

[0053] In some embodiments, the methods described herein may utilize aqueous-based insulating fluid with water-miscible organic liquid that comprise an amine, e.g. , diethyl amine, 2-aminoethanol, and 2-(dimethylamino)ethanol, and the like, and any combination thereof.

[0054] In some embodiments, the methods described herein may utilize an aqueous-based insulating fluid (or crosslinked synthetic polymer) with a crosslinker that comprises at least one of polyalkylimine, polyalkyleneimines, polyethyleneimine, and the like, any derivative thereof, and any combination thereof.

[0055] In some embodiments, the methods described herein may utilize an aqueous-based insulating fluid in an environment (e.g., in an annulus, in a pipeline, in a wellbore, and the like) such that at least a portion of the aqueous- based insulating fluid is exposed to temperatures of about 300°F or greater, about 350°F or greater, or about 400°F or greater (e.g., about 400°F to about 600°F). For example, at least one side of an annulus may be at such a temperature.

[0056] In some embodiments, the methods described herein may utilize an aqueous-based insulating fluid in an environment (e.g., in an annulus, in a pipeline, in a wellbore, and the like) that has a temperature differential across the aqueous-based insulating fluid of about 50°F or greater, about 100°F or greater, or about 150°F or greater (e.g. , about 50°F to about 200°F) . In some embodiments, the methods described herein may utilize an aqueous-based insulating fluid in an environment (e.g. , in an annulus, in a pipeline, in a wellbore, and the like) that has a temperature differential across the aqueous- based insulating fluid having less than about 1 in thickness (e.g. , the inner portion of the annulus being about 1/8 in to about 1 in thick) of about 50°F or greater, about 100°F or greater, or about 150°F or greater (e.g. , about 50°F to about 200°F). [0057] To facilitate a better understanding of the present invention, the following examples of preferred or representative embodiments are given. In no way should the following examples be read to limit, or to define, the scope of the invention.

EXAMPLES

[0058] Example 1. We studied the formulation and testing of various combinations of inorganic, organic, clay and polymeric materials for use as viscosifying/gelling agents in aqueous based fluids for insulating fluids. We conducted a series of tests in which the solubility, thermal conductivity, thermal stability, pH, gelling properties, rheological behavior, and toxicity of the various fluids were evaluated and compared. Perhaps most importantly, the thermal stability ranges from 37°F to 280°F and above were evaluated . These tests were conducted over short and long term periods. FIG. 1 lists the materials used in the formulations and the amounts tested . This in no way should be construed as an exhaustive example with reference to the invention or as a definition of the invention in any way.

[0059] Thermal stability and static aging : All formulations of fluids were statically aged at temperatures about > 280°F for two months. Formulations and properties for the tested fluids are shown in Tables 1 and 2 below. Most of the fluids appeared to remain intact, with the crosslinked systems showing an increase in viscosity and what appeared to be complete gelation behavior. We believe that these systems appeared to exhibit more desirable stability properties than other fluids, which included numerous biopolymers (e.g. , xanthan, welan, and diutan gums) and inorganic clays and were generally destroyed after 3 days at 250°F. In addition, as to the thermal stability of these formulations tested, less than 1% syneresis was observed for any of the samples.

[0060] In addition to the static tests, Sample 4 was evaluated using a high-temperature viscometer to examine the thermal activation of crosslinking agents (FIG. 2). The fluid was subjected to a low shear rate at 190°F, with viscosity measurements showing an increase with time to reach the maximum recordable level around 5000 minutes. TABLE 1

IPF Formulations and Properties Before Static Aging

Sample

1 2 3 4

Formulations

Density, ppg 8.5 10.5 12.3 11.3

Water, % vol 20 10 -- 1

Glycerol, % vol -- 90 78.5 90

PG, % vol 80 -- -- —

Brine, % vol -- -- 21.5 9

Polymer A, % wt 1 1 1 —

Polymer B, % wt -- — -- 1.25

Aldehyde, ppm 5000 5000 5000 —

HQ, ppm 5000 5000 5000 —

PEI, % wt -- — -- 2

Properties

300 rpm ¹ 280 285 270 82

Shear Strength, lb/100 ft ² 13.4 20.65 20.65 > 13.4

Thermal Conductivity ² , BTU/hft°F 0.141 0.172 0.154 0.158

¹ Measurements obtained from reading observed on Fann 35 viscometer, sample temperature 120°F

Measurements obtained by KD2-Pro Thermal Properties Analyzer.

TABLE 2

IPF Formulations and Properties After 60 Days Static Aging at 280°F

Sample

1 2 3 4

Formulations

Density, ppg 8.5 10.5 12.3 11.3

Water, % vol 20 10 -- 1

Glycerol, % vol -- 90 78.5 90

PG, % vol 80 -- -- —

Brine, % vol -- -- 21.5 9

Polymer A, % wt 1 1 1 --

Polymer B, % wt -- -- -- 1.25

Aldehyde, ppm 5000 5000 5000 —

HQ, ppm 5000 5000 5000 —

PEI, % wt -- -- -- 2

Properties

300 rpm ³ max max max max

Shear Strength, lb/100 ft ² >50 >50 >50 >50

Thermal Conductivity ² , BTU/hft°F 0.141 0.172 0.154 0.158

Fluids gelled, off-scale measurement. [0061] Thermal conductivity measurements: The importance of a low thermal conductivity (K) is an important aspect of the success of insulating fluids. For effective reduction of heat transfer, aqueous-based packer fluids in the density range of 8.5 to 12.3 ppg are expected to exhibit values for K of 0.3 to 0.2 BTU/hr ft °F, and preferably would have lower values. From the various formulations listed above, fluid densities of 8.5 to 14.4 ppg were observed, all of which have a thermal conductivity of <0.2 BTU/hr ft °F as shown in Tables 1 and 2.

[0062] Example 2. We studied the formulation and testing of various combinations of inorganic, organic, clay and polymeric materials for use as viscosifying/gelling agents in aqueous based fluids for insulating fluids. We conducted a series of tests in which the solubility, thermal conductivity, thermal stability, pH, gelling properties, rheological behavior, and toxicity of the various fluids were evaluated and compared. Perhaps most importantly, the thermal stability ranges from 37°F to 500°F and above were evaluated . These tests were conducted over short and long term periods. FIG. 3 lists the materials used in the formulations and the amounts tested . This in no way should be construed as an exhaustive example with reference to the invention or as a definition of the invention in any way.

[0063] Thermal stability and static aging : All formulations of fluids were statically aged at temperatures about >400°F for 3 day intervals. Formulations and properties for the tested fluids are shown in Tables 3 and 4 below. Most of the fluids appeared to remain intact, with the crosslinked systems showing an increase in viscosity and what appeared to be complete gelation behavior. We believe that these systems appeared to exhibit more desirable stability properties than other fluids, which included numerous biopolymers (e.g. , xanthan, welan, and diutan gums) and inorganic clays and were generally destroyed after 3 days at 250°F. In addition, as to the thermal stability of these formulations tested, less than 1% syneresis was observed for any of the samples. TABLE 3

IPF Formulations and Properties Before Static Aging

Sample

1 2

Thermal conductivity, BTU/(hft°F) 0.166 0.177

Density, lb/gal 10.5 9.5

Fann ® 35 Viscometer 150°F 150°F

600 rpm 160 161

300 rpm 125 126

200 rpm 109 102

100 rpm 84 88

6 rpm 37 40

3 rpm 34 38

PV 35 35

YP 90 91

TABLE 4

IPF Formulations and Properties After 72 Hours Static Aging at 450°F

Sample

1 2

Thermal conductivity, BTU/(hft°F) 0.166 0.177

Density, lb/gal 10.5 9.5

Fann ® 35 Viscometer 150°F 150°F

600 rpm 163 159

300 rpm 127 122

200 rpm 111 104

100 rpm 82 86

6 rpm 40 41

3 rpm 36 37

PV 36 35

YP 91 85

[0064] Thermal conductivity measurements: The importance of a low thermal conductivity (K) is an important aspect of the success of insulating fluids. For effective reduction of heat transfer, aqueous-based packer fluids in the density range of 8.5 to 10.5 ppg are expected to exhibit values for K of 0.3 to 0.2 BTU/hr ft °F, and preferably would have lower values. From the various formulations listed above, fluid densities of 8.5 to 10.5 ppg were observed, all of which have a thermal conductivity of <0.2 BTU/hr ft °F as shown in Tables 3 and 4. [0065] Example 3. In a wellbore in the field, a casing was determined to be poorly bonded to the tubing. As such, when steam was injected into the wellbore, the casing expanded, and because of poor adhesion to the tubing, extended out of the wellbore by about as much as 11 feet. When an aqueous- based insulating fluid described herein was placed between the casing and the tubing, the tubing extended out only about 3 feet. Further, with the aqueous- based insulating fluid, the steam injection operation was able to run longer with higher injection rates.

[0066] Example 4. In a deviated wellbore in the field with a casing well bonded to the tubing, the wellbore was utilized for a steam assisted gravity drainage operation. Because of the good bonding between the tubing and the casing, the tubing twists and breaks because of differential casing and tubing expansion. When an aqueous-based insulating fluid described herein was placed between the tubing and a tubing disposed therein, the twist-off was mitigated, and possibly eliminated.

[0067] Example 5. Three different biopolymer systems optionally crosslinked with multivalent ions (Sample A - crosslinked guar, Sample B - a xanthan diuten blend, and Sample C - crosslinked xanthan) and one sample of an aqueous-based insulating fluid according to the present invention (Sample D - polyacrylamide crosslinked with polyethylene imine) were tested at 300°F for 30 days. FIG. 5 provides a photograph of the four samples after aging . The biopolymer samples A, B, and C all showed phase separation and varying degrees of polymer degradation indicated by charring and discoloration. Sample A has completely charred, which in application in a subterranean operation could be catastrophic. Sample B has significant charring, and Sample C has moderate charring . The degradation seen in all three samples lead to reduced viscosity and lost gelation, which, in turn, allows for convective currents to form that increase the heat transfer properties of the fluid, i.e. , the fluid no longer functions as an insulating fluid. In contrast, Sample D of an aqueous-based insulating fluid described herein shows no phase separation and no degradation. Rather, Sample D is a clear single-phase fluid . This example illustrates the thermal stability of the aqueous-based insulating fluid of the present invention.

[0068] The exemplary aqueous-based insulating fluids disclosed herein may directly or indirectly affect one or more components or pieces of equipment associated with the preparation, delivery, recapture, recycling, reuse, and/or disposal of the disclosed aqueous-based insulating fluids. For example, the disclosed aqueous-based insulating fluids may directly or indirectly affect one or more mixers, related mixing equipment, mud pits, storage facilities or units, fluid separators, heat exchangers, sensors, gauges, pumps, compressors, and the like used generate, store, monitor, regulate, and/or recondition the exemplary aqueous-based insulating fluids. The disclosed aqueous-based insulating fluids may also directly or indirectly affect any transport or delivery equipment used to convey the aqueous-based insulating fluids to a well site or downhole such as, for example, any transport vessels, conduits, pipelines, trucks, tubulars, and/or pipes used to fluidically move the aqueous-based insulating fluids from one location to another, any pumps, compressors, or motors (e.g. , topside or downhole) used to drive the aqueous-based insulating fluids into motion, any valves or related joints used to regulate the pressure or flow rate of the aqueous-based insulating fluids, and any sensors (i.e. , pressure and temperature), gauges, and/or combinations thereof, and the like. The disclosed aqueous-based insulating fluids may also directly or indirectly affect the various downhole equipment and tools that may come into contact with the aqueous-based insulating fluids such as, but not limited to, drill string, coiled tubing, drill pipe, drill collars, mud motors, downhole motors and/or pumps, floats, MWD/LWD tools and related telemetry equipment, drill bits (including roller cone, PDC, natural diamond, hole openers, reamers, and coring bits), sensors or distributed sensors, downhole heat exchangers, valves and corresponding actuation devices, tool seals, packers and other wellbore isolation devices or components, and the like.

[0069] Embodiments disclosed herein include :

[0070] Embodiment A: A method comprising : providing an aqueous- based insulating fluid in an annulus between a riser column and an outer casing disposed thereabout, the riser column connecting a wellbore penetrating a subterranean formation to a floating surface rig; and flowing a fluid through the riser column and the wellbore.

[0071] Embodiment B : A method comprising : providing an aqueous- based insulating fluid in an annulus between a tubing and a casing disposed thereabout, the tubing and casing penetrating a subterranean formation; and flowing steam through the tubing and into the subterranean formation . [0072] Embodiment C: A method comprising : providing an aqueous- based insulating fluid in an annulus between a tubing and a casing disposed thereabout, the tubing and the casing penetrating a subterranean formation, the subterranean formation comprising permafrost; and flowing a fluid at about 40°F or greater through the tubing.

[0073] Each of embodiments A, B, and C may have one or more of the following additional elements in any combination :

[0074] Element 1 : The method wherein providing comprises placing the aqueous-based insulating fluid in the annulus, the aqueous-based insulating fluid comprising an aqueous base fluid, a water-miscible organic liquid, a synthetic polymer, and a crosslinker; and crosslinking the synthetic polymer with the crosslinker.

[0075] Element 2 : The method wherein crosslinking comprises exposing the aqueous-based insulating fluid to a temperature of about 90°F or greater.

[0076] Element 3 : The method wherein exposing occurs before placing the aqueous-based insulating fluid in the annulus.

[0077] Element 4: The method wherein exposing occurs after placing the aqueous-based insulating fluid in the annulus.

[0078] Element 5 : The method wherein the aqueous-based insulating fluid comprises an aqueous base fluid, a water-miscible organic liquid, and a layered silicate.

[0079] Element 6: The method wherein the fluid is a drilling fluid .

[0080] Element 7 : The method further comprising : performing a managed pressure drilling operation to extend the wellbore in the subterranean formation.

[0081] Element 8: The method further comprising : performing a dual gradient drilling operation to extend the wellbore in the subterranean formation.

[0082] Element 9 : The method wherein the fluid is a formation fluid.

[0083] Element 10 : The method wherein at least a portion of the aqueous-based insulating fluid is exposed to a temperature of about 250°F to about 400°F for 30 days or greater.

[0084] Element 11 : The method wherein the fluid is about 20% warmer or greater than if flowing through a similar riser without the aqueous- based insulating fluid . [0085] By way of non-limiting example, exemplary combinations applicable to A, B, C include : Embodiment A, B, or C with Elements 1 and 3; Embodiment A, B, or C with Elements 2, 4, and 8; or Embodiment A, B, or C with Elements 1, 4, and 9; etc.

[0086] Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular illustrative embodiments disclosed above may be altered, combined, or modified and all such variations are considered within the scope and spirit of the present invention. The invention illustratively disclosed herein suitably may be practiced in the absence of any element that is not specifically disclosed herein and/or any optional element disclosed herein. While compositions and methods are described in terms of "comprising," "containing," or "including" various components or steps, the compositions and methods can also "consist essentially of" or "consist of" the various components and steps. All numbers and ranges disclosed above may vary by some amount. Whenever a numerical range with a lower limit and an upper limit is disclosed, any number and any included range falling within the range is specifically disclosed . In particular, every range of values (of the form, "about a to about b," or, equivalently, "from approximately a to b," or, equivalently, "from approximately a-b") disclosed herein is to be understood to set forth every number and range encompassed within the broader range of values. Also, the terms in the claims have their plain, ordinary meaning unless otherwise explicitly and clearly defined by the patentee. Moreover, the indefinite articles "a" or "an," as used in the claims, are defined herein to mean one or more than one of the element that it introduces.