Abstract:
A thermally insulating fluid composition comprising a glycol solvent for a viscosifier, a viscosifier, and optionally, an aqueous brine. The glycol may be selected from a propylene glycol, or under excessive heat temperatures, a butylene glycol, which can be used with or without a viscosifier. Viscosifiers can be selected from hydroxy propyl methyl cellulose, xanthan and hydroxy propyl guar and combinations thereof. In one method of producing the thermally insulating composition, a viscosifier is added to an aqueous brine, water is then added to that solution followed by the addition of dry salt of the brine to increase density if necessary. A propylene glycol solvent is added to the resulting solution. The thermally insulating fluid composition insulates substances stored or transported in multi-walled vessels, tanks, piping and thermal units. A method of applying the insulating fluid composition of this invention comprising the steps of injecting the thermally insulating fluid into the cavity formed by two adjacent walls of the vessel or piping and then sealing off the opening.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a composition for a thermally insulating fluid, the method of producing a thermally insulating fluid and a method of insulating multi-walled containers. More specifically the invention relates to a thermal insulating fluid comprising one or more glycols and a viscosifier.  
         BACKGROUND OF THE INVENTION  
         [0002]    Low thermal conductivity is desirable in many industrial and consumer applications for the purposes of maintaining fluids or solids within a specific temperature range. Thermal containers for foods, insulated tanks and piping for storage and transportation of temperature sensitive fluids and oil field tubing require thermal insulating qualities under varying environmental conditions. Currently, as oil field production seeks deeper drilling, both offshore and in certain land fields, such as the atmospheric environs of Alaska, the retention of high temperatures within the tubing is necessary to inhibit the accumulation of asphaltene and paraffin inside pipes. The outer hull of particular chemical storage tanks as well must have thermal insulating qualities, for example, gasoline storage tanks and liquid ammonia tanks. Thermal properties are necessary in the ammonia storage tanks to maintain aqueous ammonia in its liquid state, requiring temperatures below 65° F.  
           [0003]    Various insulating compositions and methods are well known. One ubiquitous fluid composition used asbestos as the insulating component. Asbestos is now a known human health hazard. Its choice as an insulating component is no longer viable. Naturally porous rocks such as vermiculite and perlite have been used for insulating purposes, although, their past use has been limited to solid state compositions. In the event storage vessels or piping need to be disassembled for repair or reconditioning of the insulating material, a composition in a solid state increases down time and the repair problems because of the difficulty of removal thereby increasing cost of production.  
           [0004]    U.S. Pat. No. 4,276,936 given to McKinzie discloses a method of thermally insulating the borehole of a well. McKinzie &#39;936 teaches the use of a solid material having thermal insulating properties, such as vermiculite and perlite. The &#39;936 reference discloses that the solid insulating material is introduced into the annulus in the absence of a carrier liquid and is removed by fluidization of the material.  
           [0005]    Viscosifiers and vicosifying gels are used to fluidize solid particulates. U.S. Pat. No. 4,530,402 given to Smith et al. discloses the use of a low density spacer fluid and then displacing the low density fluid with a completion fluid such as cement slurry. The Smith &#39;402 reference teaches the low density spacer fluid is comprised of a carrier fluid, which can contain a viscosifying agent, and discrete dispersible density reducing bodies. The &#39;402 reference teaches the use of dispersible reducing bodies such as hollow spheres in the spacer fluid. Smith &#39;402 teaches that the hollow spheres aid in reducing the hydrostatic head of the spacer fluid.  
           [0006]    U.S. Pat. No. 3,360,046 given to Johnson et al. discloses a cement slurry with insulating properties for use in wells. The &#39;046 reference teaches the use of 25% to 40% silica flour, and from 10% to 50% of vermiculite or perlite. Also, the &#39;046 reference mentions that a gelling agent, such as bentonite can be present in the cement composition. Also, a dispersing agent can be used in the cement slurry.  
           [0007]    U.S. Pat. No. 4,780,220 given to Peterson discloses a method of preparing a drilling and completion fluid. Peterson &#39;220 teaches a drilling mud comprising water, a gelling agent, a defoamer, and at least 6% by volume of a glycerine. Glycol is used as the defoamer and water comprises at least 22%-28% of the composition.  
           [0008]    U.S. Pat. No. 6,103,671 given to Dobson relates to water-based well working fluids in drilling, completing, or workover of oil and gas wells. The &#39;671 fluid comprises an amorphous silica viscosifier and a water soluble polyethylene glycol shale inhibitor, the silica viscosifier added in an amount to increase the thermal stability of the fluid.  
           [0009]    An oil-free water-soluble hydroxyethyl cellulose liquid polymer dispersion is disclosed by Hoff in U.S. Pat. No. 5,985,801. The &#39;801 polymer dispersion is used for thickening aqueous mediums of completion and workover fluids. The dispersion comprises hydroxyethyl cellulose and propylene glycol derivatives including propylene glycol polyether polyols and aliphatic propylene glycol ether. The hydroxyethyl cellulose is dispersed rather than dissolved in the propylene glycol derivatives.  
           [0010]    The compositions of both U.S. Pat. No. 5,876,619 given to Skaggs et al. and U.S. Pat. No. 5,290,768 given to Ramsay et al. are directed towards insulating fluids. Ramsay discloses a thixotropic composition containing ethylene glycol and glycol-compatible welan gum. Ramsey narrowly claims a composition consisting of ethylene glycol, a chelating agent and glycol compatible welan gum in a 0.25% mixture with ethylene glycol. Skaggs is specifically directed towards scleroglucan as a viscosifier in a polyol base of glycerin or ethylene glycol wherein the scleroglucan is 1% to 3% by weight of the composition and the composition contains less than 10% water, preferably 1% to 5% by weight of the composition. Skaggs suggests various uses for the composition in addition to thermal insulation, including de-icing, ballasting, as a packer material and reservoir work over completion “kill” material.  
           [0011]    Several problems are associated with prior insulating compositions, a primary concern being that they can react with the chemicals that are being stored or piped. In the case of a leak, the composition could chemically react with the contents to form a hazardous situation. Compositions in a solid state tend to be porous and would allow the travel of leaked chemicals. Gels have been used to restrict the movement of leaking chemicals.  
           [0012]    Insulating compositions can decompose over time. Some fluids will separate over time or chemically degrade. A composition with an insulating component needs to withstand the effects of time to maintain its ability to insulate. A thermally insulating fluid is needed that provides insulation to fluids in vessels and pipes without breaking down or reacting with the stored fluids if leakage occurs.  
         SUMMARY OF THE INVENTION  
         [0013]    The thermally insulating fluid of this invention has relatively low thermal conductivity as compared to previously known insulating fluids and is stable over periods of time so as to resist phase separation or decomposition. Advantageously, the thermally insulating fluid has the rheological properties required to support the insulating fluid components and yet is pumpable so that it can be removed from the insulating container or piping if necessary. One preferred thermally insulating fluid composition comprises a glycol solvent, preferably a propylene glycol solvent, a viscosifier, and optionally, an aqueous brine or other weighting agent. Under high temperature conditions, such as deep downhole drilling, a butylene glycol can be used as the insulating agent in combination with an aqueous brine, and, depending on temperature, the composition comprises butylene glycol as the solvent for a viscosifier and an aqueous brine.  
           [0014]    The thermal insulating fluid composition of the present invention advantageously has lower thermal conductivity thereby increasing its insulating properties. Glycol, preferably, propylene glycol is advantageously used as the insulating agent and solvent for a viscosifier in the present composition because it has been found that the propylene glycol in combination with one or more viscosifiers have the desired lower conductive properties to produce better insulators. One preferred composition can comprise a glycol solvent, preferably a glycol solvent with selected viscosifiers, for example, hydroxy propyl methyl cellulose, hydroxy propyl guar, xanthan, and combinations thereof, either with or without an aqueous brine solution.  
           [0015]    Weighting agents can be used to yield a variety of densities to meet hydraulic and thermal requirements. One novel aspect of the present invention is the combination of a glycol, preferably propylene glycol, as a solvent for one or more of the selected viscosifiers with a weighting agent selected from a group consisting of soluble organic salts, soluble inorganic salts, particulate minerals and combinations thereof.  
           [0016]    In another aspect, the present invention comprises a thermal insulating fluid of propylene glycol solvent with one or more viscosifiers measuring about 0.1% by weight to about 10% by weight. The propylene glycol solvent measures about 20% to 99.9% by weight with one or more viscosifiers selected from xanthan, hydroxy propyl methyl cellulose, hydroxy propyl guar and combinations thereof. Optionally, aqueous brine concentrations measuring 0.1% to 79.9% may be added. The salt of the aqueous brine is selected from NaCl, NaBr, KCl, KBr, CaCl 2 , CaBr 2 , ZnCl 2 , ZnBr 2 , NaNO 3 , KNO 3 , Ca(NO 3 ) 2 , Zn(NO 3 ) 2  and combinations thereof.  
           [0017]    In another embodiment, especially useful in high temperature environments, the thermal insulating fluid of the present invention comprises butylene glycol and an aqueous brine. Preferably, under high temperature conditions, one or more viscosifiers can be added to the mixture of butylene glycol and brine, wherein the butylene glycol will act as the solvent for the viscosifiers. Alternatively, the glycol solvent can comprise a combination of propylene glycol and butylene glycol. Depending on temperature conditions one or more viscosifiers can be added. The concentrations of the glycol solvents, viscosifiers and aqueous brine, if added, remain equivalent to the propylene glycol thermally insulating fluid described above.  
           [0018]    In a further aspect, the present invention provides a method for producing a thermal insulating fluid by adding a first viscosifier to an aqueous brine. The viscosifier can be selected from hydroxy propyl methyl cellulose, xanthan and hydroxy propyl guar and combination thereof. Water is then added followed by a dry salt or concentrated brine to increase the density. In a separate vessel, a second viscosifier is added to a glycol solvent. The final step combines the contents of both vessels to form the more stable thermal insulating fluid of this invention.  
           [0019]    Another preferred method for producing a thermal insulating fluid utilizing two viscosifiers comprises the steps of: (a) adding a first viscosifier to an aqueous brine;(b) adding water to the mixture of step (a); (c) adding a dry salt or concentrated brine to increase density; (d) in a separate vessel, adding a second viscosifier to propylene glycol; (e) combining the mixture of step (c) to the mixture of step (d).  
           [0020]    In this preferred method for producing a thermal insulating fluid, the first and second viscosifiers are selected from hydroxy propyl methyl cellulose, xanthan and hydroxy propyl guar and combinations thereof  
           [0021]    Thermally insulating fluid can be used with multi-walled vessels such as thermal units, tanks, or concentric piping wherein two walls of the unit form a sealable cavity for receiving the insulating fluid. Concentric piping for transporting fluids subject to varying temperature conditions require removable insulating fluids to maintain the temperature of the fluids being piped, pumping hydrocarbons for on/off shore oil and gas fields, for example. Double-walled tanks that are used to store chemicals which must be maintained at a specific temperature also benefit from this insulating composition. One example of such a use is the storage of highly volatile liquids, namely gasoline or aqueous ammonia. This invention is also applicable to other thermal units, including coolers and refrigeration units, that have the common problem of undesirable heat transfer. One preferred method of applying the insulating fluid composition of this invention is to inject the thermally insulating fluid into the cavity formed by the walls of the vessel or piping and then seal off the opening. If the insulating fluid needs to be removed, the opening can be unsealed and the insulating fluid pumped out in ways commonly known in the art.  
           [0022]    The thermally insulating fluids may either be used alone or in combination with other insulating materials such as vacuum insulated tubing; insulation coated tubing and particulate insulating materials, namely plastics, glass beads, foams and hollow spheres.  
         DETAILED DESCRIPTION OF THE INVENTION  
         [0023]    The present invention relates to an innovative thermal insulating fluid, a method of producing the thermal insulating fluid and methods of insulating that are used to reduce heat transfer. The insulating fluid and method of application of the composition of this invention is especially effective when used with multi-walled containers by insertion of the fluid into a sealable cavity defined by the walls. The low heat conduction properties of the present thermal insulating fluid allows it to be applicable in either extremes of temperature, high heat found in deep well drilling or piping in the frozen tundra for example.  
           [0024]    In one preferred embodiment, the composition of the present thermal insulating fluid comprises a glycol solvent for viscosifiers, one or more viscosifiers, and, optionally an aqueous brine. Glycols exhibit good insulating properties when, according to the composition of this invention, they are used as a solvent for a viscosifier. In one preferred composition, the glycol is a propylene glycol that can be selected from mono-propylene glycol, di-propylene glycol, tri-propylene glycol, tetra-propylene glycol or combinations thereof. The one or more viscosifiers can be selected from hydroxy propyl methyl cellulose commercially available as Methocell OS from the Dow Chemical Co., xanthan commercially available as Rhodopol 23 from Rhodia, hydroxy propyl guar commercially available as Jaguar 413 from Rhodia, and combinations thereof.  
           [0025]    When thermal insulation is required under high temperature conditions, the glycol can be butylene glycol and one preferred thermal insulating fluid comprises butylene glycol in an aqueous brine. Because butylene glycol is viscous at lower temperatures, additional viscosifiers are not necessary until the butylene glycol thermal insulating fluid is considered for use under higher temperatures conditions, above 190° F., for example. Butylene glycol can be selected from 1,2 butylene glycol, 2,3 butylene glycol, 1,3 butylene glycol, 1,4 butylene glycol, or combinations thereof.  
           [0026]    One preferred embodiment of the thermal insulating fluid comprises a propylene glycol solvent for a viscosifier and a viscosifier. The glycol is the solvent and water content of the fluid can range from about 0.1% to about 5.0%. Alternatively, an aqueous brine may be added as a weighting agent. In one aspect, the preferred thermal insulating fluid comprises a propylene glycol used as a solvent for viscosifiers in an amount comprising about 20% to 99.9% by weight, and one or more viscosifiers in an amount comprising about 0.1% by weight to about 10% by weight. In this composition, the one or more viscosifiers can be selected from xanthan, hydroxy propyl methyl cellulose, hydroxy propyl guar or combinations thereof. An alternative composition utilizing an aqueous brine can comprise a propylene glycol solvent for viscosifiers in an amount comprising about 20% to 99.8% by weight, one or more viscosifiers in an amount comprising about 0.1% by weight to about 10% by weight, the one or more viscosifiers selected from xanthan, hydroxy propyl methyl cellulose, hydroxy propyl guar and combinations thereof; and 0.1% to 79.9% aqueous brine.  
           [0027]    Another preferred thermal insulating fluid comprises a propylene glycol solvent for viscosifiers, viscosifiers in an amount comprising about 0.1% by weight to about 10% by weight, the propylene glycol in an amount comprising about 20% to 99.8% by weight, the viscosifiers comprising xanthan and hydroxy propyl guar and 0.1% to 79.9% aqueous brine.  
           [0028]    Under high temperature industrial processes such as deep well drilling, the present invention utilizes a thermal insulating fluid comprising a butylene glycol and an aqueous brine. Alternatively, the thermal insulating fluid comprises a butylene glycol solvent for viscosifiers and one or more viscosifiers. The addition of an aqueous brine is optional. In still another alternative composition, useful under higher geothermal conditions, the thermal insulating fluid is a combination of a propylene glycol solvent and a butylene glycol solvent for viscosifiers, the viscosifiers in an amount comprising about 0.1% by weight to about 10% by weight, the combination of propylene glycol and butylene glycol in an amount comprising about 20% to 99.8% by weight, the viscosifiers selected from xanthan, hydroxy propyl methyl cellulose, hydroxy propyl guar and combinations thereof. An addition of 0.1% to 79.9% aqueous brine is optional. In one aspect, the viscosifiers comprise xanthan and hydroxy propyl guar.  
           [0029]    The weighting agents used in the practice of this invention can be selected from a group consisting of soluble inorganic salts, soluble organic salts, particulate minerals and combinations thereof. In one embodiment, the one or more soluble inorganic salts are selected from NaCl, NaBr, KCl, KBr, CaCl 2 , CaBr 2 , ZnCl 2 , ZnBr 2 , NaNO 3 , KNO 3 , Ca(NO 3 ) 2 , Zn(NO 3 ) 2  and combinations thereof. Alternatively, the weighting agent can be one or more soluble organic salts selected from sodium formate, potassium formate, and/or cesium formate and combinations thereof. The organic salt weighting agent can also be selected from sodium acetate, potassium acetate, and combinations thereof. Alternatively, weighting agents can also be selected from one or more particulate minerals such as hematite, magnetite, illmenite, barite, siderite, celestite, dolomite, calcite, scheelite, apatite and combinations thereof.  
           [0030]    Plastics, microspheres, glass beads and combinations thereof can also be used as additional insulating materials or weighting agents. In one preferred embodiment, the insulating particulates comprise microspheres such as glass microspheres, either solid glass or hollow. If hollow, the glass preferably comprises sufficient compressive strength to withstand a pressure range from about 10 psi to about 10,000 psi. The compression strength of the glass shell is selected according to the environment of the application of insulating fluid. In one preferred embodiment, the insulating particulates comprise a combination of insulating hollow glass microspheres and insulating solid particulates, for example, insulating hollow glass microspheres and solid glass microspheres.  
           [0031]    Alternatively the insulating particulates can comprise plastic microspheres, also having compressive strength to withstand downhole pressures. The hollow insulating particulates, glass or plastic, can encapsulate a fluid. The cavity of the hollow spheres, can be filed with a gas or liquid. Preferably the particulates encapsulate air, air being one of the better insulators. Additional insulating materials comprise vacuum insulated tubing, insulation-coated tubing, foams, and phase change materials in the form of coatings or particles.  
           [0032]    In another aspect of this invention, one preferred thermal insulating fluid comprises a propylene glycol solvent for a viscosifier and hydroxy propyl methyl cellulose. The addition of an aqueous brine is optional. Another preferred thermal insulating fluid comprises a propylene glycol solvent for a viscosifier and a combination of xanthan and hydroxy propyl guar, optionally an aqueous brine can be added to the fluid.  
           [0033]    One preferred method for producing thermal insulating fluid of this invention comprises the following:  
           [0034]    (a) adding a viscosifier to an aqueous brine;  
           [0035]    (b) adding water to the mixture of step (a);  
           [0036]    (c) adding a dry salt or concentrated brine to increase density;  
           [0037]    (d) adding propylene glycol to the mixture of step (c).  
           [0038]    An alternative method utilizing two viscosifiers comprises the steps of:  
           [0039]    (a) adding a first viscosifier to an aqueous brine;  
           [0040]    (b) adding water to the mixture of step (a);  
           [0041]    (c) adding a dry salt or concentrated brine to increase density;  
           [0042]    (d) in a separate vessel, adding a second viscosifier to propylene glycol;  
           [0043]    (e) combining the mixture of step (c) to the mixture of step (d).  
           [0044]    In this method for producing a thermal insulating fluid the first and second viscosifiers are selected from hydroxy propyl methyl cellulose, xanthan and hydroxy propyl guar and combinations thereof.  
           [0045]    One preferred method for producing a thermal insulating fluid having xanthan and guar as viscosifiers comprises:  
           [0046]    (a) adding xanthan to an aqueous brine;  
           [0047]    (b) adding water to the mixture of step (a);  
           [0048]    (c) adding a dry salt or concentrated brine to increase density;  
           [0049]    (d) in a separate vessel, adding hydroxyl propyl guar to propylene glycol;  
           [0050]    (e) combining the mixture of step (c) to the mixture of step (d).  
           [0051]    The aqueous brine can be selected from NaCl, NaBr, KCl, KBr, CaCl 2 , CaBr 2 , ZnCl 2 , ZnBr 2 , NaNO 3 , KNO 3 , Ca(NO 3 ) 2 , Zn(NO 3 ) 2  and combinations thereof. Any of the above methods can further comprise the addition of a second viscosifier, hydroxyl propyl guar for example, to a combination of propylene glycol and butylene glycol in step (d).  
           [0052]    The usefulness of the thermally insulating fluid described herein is multifold. Concentric piping for transporting fluids subject to varying temperature conditions often require removable insulating fluids to maintain the temperature of the fluids being piped, pumping hydrocarbons on shore or offshore, for example. Double-walled tanks that are used to store chemicals which must be maintained at a specific temperature also benefit from this insulating composition. One example of such a use is the storage of highly volatile liquids such as gasoline or aqueous ammonia. This invention is also applicable to other thermal units, including coolers and refrigeration units that have the common problem of undesirable heat transfer.  
           [0053]    One effective use of the thermally insulating fluid is in oil field production to protect the loss of heat in subterranean piping that is subject to cold weather conditions, deep sea wells, Arctic drilling, Alaska and similar environments. Many such wells have several concentric layers of piping so that the double-wall cavity is available for receiving the injected insulating fluid. Protecting the permanently frozen ground, such as permafrost from the heat of pipes transporting petrochemicals is another consideration. The injection of the thermally insulating fluid of this invention between double-walled piping can reduce damage to the permafrost.  
           [0054]    For the purpose of illustration, reference hereafter is made, for convenience and not to limit the scope of this composition or its methods. The detailed description will describe the composition and use of insulating fluid in downhole pipe used in oil field production. The retention of high temperatures within the tubing is necessary to inhibit the accumulation of asphaltene, paraffin and scale inside pipes. The presence of hydrates or paraffins in pipe will slow down products from traveling through the pipe and reduce or halt production. Downhole piping typically comprises casing, tubing for drilling fluids and the production of the hydrocarbons and several intermediate layers of pipe. The thermally insulating fluid of this invention is injected in the annulus or cavity created by two adjacent walls of piping thereby protecting the high temperatures of the production fluids from the cold temperatures of the subterranean environment.  
           [0055]    One method of insulating multi-walled systems comprises injecting a thermally insulating fluid having a composition as described above in between two adjacent walls of a multi-walled or concentric walled system. The concentric walls of the system form an annulus or cavity. The insulating fluid of this invention can be injected into this cavity and then the cavity is sealed. Advantageously, removal of the insulating fluid can be accomplished by standard, known pumping methods because of the fluid nature of the insulation of this invention.  
           [0056]    One method of insulating multi-walled pipes comprises injecting a thermally insulating fluid comprising one of the above-described compositions into the annulus or cavity defined by two of the walls of the multi-walled or concentric piping. This method is adapted to insulate subterranean pipes in low temperature conditions, deep-sea bed piping for example. The thermally insulating fluid can comprise an insulating microspheres or foam, such as aphrons. A method for protecting permafrost can comprise insulating double-walled pipes laid within the permafrost by injecting the annulus between the adjacent walls with a thermally insulating fluid having one of the above-described compositions. The cavity can be sealed.  
           [0057]    Similarly, a method of insulating double-walled tanks comprises injecting the thermally insulating fluid of the present invention into the annulus defined by the adjacent walls of the tanks. The annulus can be sealed and then reopened if the insulating fluid needs to be removed. Removal is by commonly known methods of pumping fluids. Double-walled insulating vessels such as thermal packs or coolers can be insulated by inserting the thermally insulating fluid of this invention between the adjacent walls of the vessels. A method of insulating double-walled refrigeration units comprises inserting the thermally insulating fluid having the composition described above between the adjacent walls of the refrigeration units. A specialized use for the thermally insulating fluid of this invention is with protecting subsea wellheads subjected to temperature extremes. The method of insulating a subsea well head and its control equipment comprises surrounding the subsea well head and its control equipment with a container, a flexible sac for example, that encloses a thermal insulating fluid having a composition selected from a group consisting of compositions as described above. 
       
    
    
     EXAMPLES  
       [0058]    The thermal conductivity of propylene glycols of this invention is significantly lower than the thermal conductivity of glycerin or ethylene glycol of the prior art as illustrated by the following table:  
         [0059]    Thermal Conductivity Comparison Data  
                                                           Comparison of Polyol Thermal Conductivities                    % Difference Vs       Material   btu/hr-ft-° F.   Tri-Propylene Glycol                    Glycerin   0.164   80       Ethylene Glycol   0.153   68       Mono-Propylene Glycol   0.119   31       Di-Propylene Glycol   0.095   4       Tri-Propylene Glycol   0.091   0                  
 
         [0060]    The thermal conductivity data for the glycerin, ethylene glycol and mono-propylene glycol are from  Perry&#39;s Chemical Engineer&#39; Handbook,  6 ed., 1984. The data for the remaining materials are from manufacture&#39;s literature.  
       Example 1  
       [0061]    It has been determined that scleroglucan is not an effective viscosifier for propylene glycols. U.S. Pat. No. 5,876,619 teaches the viscosification of glycerin or ethylene glycol by the addition of 1% to 3% scleroglucan and heating the mixture to 195° F. for two hours, then cooling. In an effort to apply U.S. Pat. No. 5,876,619 to the viscosification of propylene glycol, 4 grams of scleroglucan (Biovis by SKW) was added to 356 grams of propylene glycol (Drillcol 7234 by Shrieve Chemical). This resulted in a 1.1 weight % mixture. The mixture was heated to 195° F., held for two hours, and then cooled to room temperature. The mixture of scleroglucan and propylene glycol did not viscosity and the scleroglucan settled out of the mixture as a solid on standing. From this experiment it is concluded that scleroglucan is not soluble in propylene glycol.  
       Example 2  
       [0062]    Thermal Conductivity Heat Capacity Test Results  
         [0063]    Below is the composition of three samples used for testing.  
                                                                             Sample A   Sample B   Sample C                                        Density    8.5    8.67    9.5           ppg           (pounds           per gallon)           Wt. %    0%    5%    26%           14.2 ppg           propylene   356   345.5   293.9           glycol           14.2 ppg    0    18.3   104.5           CaBr2           hydroxy    4    2    2           propol           methyl           cellulose           biocide    0    0.1    0           oxygen    0    0.05    0           scavanger           corrosion    0    0.05    0           inhibitor                      
 
         [0064]    Sample A is manufactured by making viscosified propylene glycol. The viscosified propylene glycol is heated to between 180° F. and 200° F. and mixed for about 2 hours.  
         [0065]    Samples B and C are manufactured by separately making viscosified brine and viscosified propylene glycol. Viscosified brine is added to the viscosified propylene glycol and mixed for 1 hour.  
         [0066]    The thermal properties of the three sample formulations containing propylene glycol and 14.2 ppg brine have been measured by an outside laboratories, Anter Laboratories, 3M Laboratories and SRI.  
         [0067]    Multiphase Systems, Inc. (MSi) has computer estimated the cool down times for a dual production riser system using the propylene glycol+14.2 ppg brine gels as follows:  
                                                                           TABLE 1                           Thermal Properties and MSi Cool Down Times                weight       Cp   K   Cool   %           %   Density   (Btu/   (Btu/   Down   Improve-       Sample ID   brine   (ppg)   lb-° F.)   hr-ft-° F.)   (hrs)   ment                    [Commer-       9.5   0.510   0.280   3.3   Basis       cially       available       product]]       Sample A    0%   8.5   0.590   0.0924   7.8   136%       Sample B    5%   8.67   0.553   0.0953   7.6   130%       Sample C   26%   9.5   0.471   0.1063   6.6   100%                  
 
       Example 3  
       [0068]    Description of Typical Composition and Manufacturing Process  
                                                           Method of producing Viscosified Propylene Glycol                    Lab       step   Description   Barrel*                    1   Add 14.2 ppg CaBr2 brine to vessel.    393.8 g       2   Slowly add xanthan biopolymer powder.    5.00 g       3   Mix 15 minutes to homogenize.       4   Add water to make 12.5 ppg brine.    94.20 g       5   Mix 40 minutes. Batch will become           very viscous.       6   Slowly add dry CaBr2 to make 14.2 ppg.   108.00 g       7   Continue mixing while preparing    339.3 g           viscosified propylene glycol.       8   In a separate vessel add propylene glycol.    339.3 g       9   Add guar gum to propylene glycol.     8.0 g       10   Mix 2 hours.       11   Allow mixing to increase temperature    339.3 g           to at least 90 F.       12   Slowly inject viscosified brine from    38.3 g           Step 6 into viscosified           propylene glycol from Step 9 with           vigorous mixing with a           Hamilton Beach mixer.       13   Mix 1 hour       14   Add Biocide    0.05 g       15   Add a corrosion inhibitor**    0.05 g       16   Add an oxygen scavenger***     0.1 g       17   Continue mixing 30 minutes until mixture           is homogeneous.       18   Sample and measure Fann 35 viscosity.