Abstract:
The present invention is directed to an oil-free, water-soluble, liquid, polymer dispersion for use in thickening aqueous mediums, particularly completion and workover fluids used in the oil and gas drilling business. The dispersions of the present invention are comprised of hydroxyethyl cellulose and propylene glycol derivatives, preferably both propylene glycol polyether polyols and an aliphatic propylene glycol ether. Optionally these dispersions include water. Because of their low toxicity, these dispersions are particularly useful for drilling in offshore environments. These compositions rapidly disperse in and viscosity a variety of brines, including sea water and other light brines, with minimum shear and without fisheye formation.

Description:
This application claims benefit from provisional application No. 60/005,394 filed Oct. 11, 1995. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to compositions for use as thickening agents in aqueous systems and to aqueous well servicing fluids prepared therefrom. More specifically, the present invention relates to liquid, polymer-containing compositions for use as thickening agents to viscosify brines to provide thickened aqueous well drilling and treating fluids. 
     2. Description of the Background 
     The use of polymers in fluids, and particularly in brines, used in well drilling and treating fluids, to improve viscosity, solids removal and/or filtration control is well known. Hydroxyethyl cellulose (HEC) has typically been the preferred hydrophilic, polymeric material chosen to provide the desired thickening of brines in the oil and gas drilling industry. Compositions including HEC have long been used to viscosify drilling fluids, workover fluids, completion fluids, packer fluids, well treating fluids, subterranean formation treating fluids, spacer fluids, hole abandonment fluids and other aqueous fluids in which an increase in viscosity is desired. 
     Hydroxyethyl cellulose, however, does not come without its own problems. Attempts to directly incorporate HEC into a well servicing fluid as a dry powder result in the formation of fisheyes, i.e., unhydrated lumps of polymer which can result in operational problems. Potential problems include the blinding of shaker screens and the plugging of the formation. 
     Hydroxyethyl cellulose is not readily hydrated, solvated or dispersed in aqueous systems without the use of elevated temperatures and/or mixing under high shear for extended periods of time. In many cases, and particularly in workover operations, the equipment available for preparing the well servicing fluids does not readily lend itself to high temperature, high shear mixing. HEC polymers are particularly poorly hydrated, solvated or dispersed in aqueous solutions containing one or more water-soluble salts of multivalent cations such as heavy brines which are commonly used in well servicing fluids. 
     One successful attempt to solve these problems was disclosed in U.S. Pat. No. 4,330,414, incorporated herein by reference. The &#39;414 patent disclosed a water miscible, polar, organic liquid for use as a solvating agent to form a semi-solid to viscous mixture with the hydroxyethyl cellulose. 
     In another approach to solving these problems, the polymer was added in the form of a solution, colloid or other suspension dispersed in a non-solvent carrier medium, e.g., an oil-based liquid such as diesel oil or kerosene. For example, see U.S. Pat. No. 4,622,153, incorporated herein by reference. However, it was found that compositions prepared in accord with the disclosure of the &#39;153 patent experienced undesirable settling and hard packing of the HEC when stored under static conditions for extended periods of time. Resuspension and dispersion of the HEC was a time consuming process and required special equipment. Accordingly, solutions prepared in accord with the disclosure of the &#39;153 patent were not conducive to use at on-site drilling, workover or completion operations. 
     Another effort to solve these problems was disclosed in U.S. Pat. No. 4,615,740, incorporated herein by reference. The &#39;740 patent disclosed a liquid, polymer-containing composition for viscosifying oilfield brines including, in addition to hydroxyethyl cellulose, an oil-based liquid, an aluminum phosphate compound and optionally a surfactant. 
     While the thickening compositions described in the foregoing patents have been successful, changing times have created a need for new and improved thickening compositions. Environmental concerns, and particularly toxicity concerns, have arisen with respect to well servicing fluids including oil-based components such as those described above. As the number of offshore drilling operations has proliferated and as environmental concerns have increased, the continued use of these prior compositions has become unacceptable. Recent changes to the NPDES Offshore Discharge Permit requirements prohibit the discharge of fluids containing oil into offshore environments. The changes essentially prohibit the use of oil-containing products in offshore environments where discharge may occur. Accordingly, oil-free completion and workover fluids, including oil-free thickening agents, must be used in operations in environmentally sensitive areas covered by these regulations. 
     Therefore, there has developed a pressing need in the well servicing industry to develop and implement the use of safer and less toxic well servicing fluids. The present invention solves that need. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a flowable, polymer composition for thickening aqueous mediums and, particularly, to aqueous well servicing fluids including that composition. These liquid polymer compositions are particularly useful in thickening light brines used in workover and completion operations. These compositions advantageously provide safe thickeners characterized by reduced toxicity for effectively and rapidly viscosifying light brines, including saltwater, with minimum shear. These compositions are particularly favorable for use in environmentally sensitive areas such as drilling, completion and workover operations on offshore platforms. 
     The compositions of the liquid polymer dispersions of the present invention generally comprise hydroxyethyl cellulose and at least one water-soluble propylene glycol derivative having a molecular weight in the range of about 260-6000. Optionally these dispersions may include water. The propylene glycol derivative is selected from the group consisting of the propylene glycol polyether polyols, the aliphatic propylene glycol ethers and mixtures thereof. In a more preferred embodiment, at least two propylene glycol derivatives, a first derivative selected from the propyleneglycol polyether polyols and a second derivative selected from the aliphatic propylene glycol ethers, are included in the liquid polymer dispersion. The presently preferred propylene glycol polyether polyols are selected from the group consisting of polypropylene glycols having the formula ##STR1## where x is about 2-50 and the polyoxypropylene polyols having the formula ##STR2## where y is about 1-32. The presently most preferred compositions include propylene glycol polyether polyols in accord with both of the foregoing formulae where x is 3 and y is 1, together with tripropylene glycol methyl ether, hydroxyethyl cellulose and water. 
     Well servicing fluids in accord with the present invention comprise an aqueous medium together with an effective amount of a thickening agent comprising a liquid, polymer composition in accord with the above formulations. The aqueous medium may comprise saltwater or other conventional light brines, including aqueous solutions of at least one water-soluble salt of a monovalent or a divalent ion. Typically, these salts include the chlorides and bromides of sodium, potassium and calcium, together with mixtures thereof. The liquid polymer dispersions of the present invention are particularly useful to effectively and safely thicken aqueous mediums having a density from about 8.5-13.5 pounds per gallon. While these dispersions may be used at the rate of about 1-10 pounds of dispersion per 42 gallon barrel of well servicing fluid, typically, only about 2-3 pounds per barrel are required for satisfactory results. 
     Liquid polymer dispersions prepared in accord with the foregoing formulations have exhibited 96 hour LC 50  values of 335,000 ppm at 10 pounds per barrel. Accordingly, dispersions and well servicing fluids prepared in accord with the present invention are significantly safer and less toxic than conventional oil-based compositions. Thus, the long felt but unfulfilled need in the oil and gas drilling and service industry for safer, less toxic thickeners and well servicing fluids has been met. These and other meritorious features and advantages of the present invention will be more fully appreciated from the following detailed description and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other features and intended advantages of the present invention will be more readily apparent by the references to the following detailed description in connection with the accompanying drawing wherein the single FIGURE is a graphic illustration of the effect on permeability of a Berea sandstone core of amorphous fused silica in a composition of the present invention. 
     While the invention will be described with reference to the presently preferred embodiments, it will be understood that it is not intended to limit the invention to those embodiments. On the contrary, it is intended to cover all alternatives, modifications and equivalents as may be included in the spirit of the invention as defined in the appended claims. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides an oil-free, liquid, polymer dispersion for use in thickening well servicing fluids. The disclosed compositions are oil-free to the extent that they produce no sheen on the surface of seawater when discharged in an offshore environment. All of the components of these compositions are soluble or miscible with water. The compositions are pourable yet contain high polymer content, e.g., up to 40 percent-by-weight hydroxyethyl cellulose. Finally, the compositions of the present invention are stable during extended, static storage. The polymer has remained suspended in formulations prepared in accord with the present invention for a period of at least three months, at the conclusion of which no settling or packing was observed. These compositions rapidly disperse in seawater and other light brines without the formation of fisheyes. Finally, these compositions can effectively viscosify non-zinc brines with a minimum of shear. 
     Thickening compositions prepared in accord with the present invention and providing all of the foregoing advantages comprise hydroxyethyl cellulose, together with propylene glycol derivatives having a molecular weight from 260-6000. The preferred propylene glycol derivatives are the aliphatic propylene glycol ethers and the propylene glycol polyether polyols, more specifically the polypropylene glycols and polyoxypropylene polyols. The presently most preferred polyether polyols are the polypropylene glycols of the following formula ##STR3## where x is about 2-50 and the polyoxypropylene polyols of the following formula ##STR4## where y is about 1-32. The presently most preferred derivatives are the polyols of the foregoing formulae where x is 3 and y is 1 together with tripropylene glycol methyl ether. All of the propylene glycol derivatives are soluble in water and seawater. 
     In its broadest embodiment, the formulations of thickening dispersions in accord with the present invention may be summarized as follows: 
     
                       TABLE 1______________________________________Broadest Formulations  Composition, % by weight              Broad     Preferred                               Optimum______________________________________hydroxyethyl cellulose          10-40     30-40    35  propylene glycol derivatives 52-90 52-65 60  water 0-8 5-8  5______________________________________ 
    
     Formulations for more preferred embodiments of the present invention wherein the compositions include both an aliphatic propylene glycol ether and propylene glycol polyether polyols may be summarized as follows: 
     
                       TABLE 2______________________________________Preferred Formulations  Composition, % by weight               Broad     Preferred                                Optimum______________________________________hydroxyethyl cellulose           10-40     30-40    35  propylene glycol polyether 22-85 28-45 40  polyols  aliphatic propylene glycol ether  5-30 20-24 20  water 0-8 5-8  5______________________________________ 
    
     Formulations for even more preferred embodiments including both a polypropylene glycol and a polyoxypropylene polyol, together with an aliphatic propylene glycol ether, may be summarized as follows: 
     
                       TABLE 3______________________________________More Preferred Formulations  Composition, % by weight               Broad     Preferred                                Optimum______________________________________hydroxyethyl cellulose           10-40     30-40    35  propylene glycol 10-75 18-25 25  polyoxypropylene polyol  5-35 10-20 15  aliphatic propylene glycol ether  5-30 20-24 20  water 0-8 5-8  5______________________________________ 
    
     Finally, formulations for the presently most preferred embodiments may be summarized as follows: 
     
                       TABLE 4______________________________________Most Preferred Formulations  Composition, % by weight               Broad     Preferred                                Optimum______________________________________ARCOL ® POLYOL PPG-425           10-75     18-25    25  ARCOL ® POLYOL LG-650  5-35 15 15  ARCOSOLV ® TPM  5-30 20-24 20  Water 0-8 5-8  5  Aqualon HEC 250 HHRX 10-40 35 35______________________________________ 
    
     Arcol and Arcosolv are trademarks of Arco Chemical. 
     The columns labeled Broad disclose the ranges of the various components that will produce a useable product. The formulations in the Broad column that do not fall in the Preferred column are deficient in one or more of three categories: the polymer activity may be too low for practical application, the composition may be too thick to be readily poured or the composition may not be stable for an extended period of time. The unstable formulations are, however, functional and will remain suspended and will function satisfactorily if used within a few days to a few weeks of preparation. The column labeled Preferred indicates the ranges of the various components which will produce useful compositions exhibiting good long term stability, with varying degrees of pourability. The optimum formulations have both good long term stability and are the most pourable of the recommended formulations. 
     Compositions prepared in accord with the present invention exhibit very low human and environmental toxicity. The 96-hour LC 50  at 10 lb/bbl for an exemplary composition prepared in accord with the present invention was 335,000 ppm. This value is a marked improvement over the values exhibited by two, conventional vicosifying agents: 106,700 ppm at 2.0 lb/bbl for BROMI-VIS® and 106,700 ppm at 8.0 lb/bbl for LIQUI-VIS NT. BROMI-VIS and LIQUI-VIS NT are registered trademarks of Baroid Technology, Inc. and represent products made in accord with U.S. Pat. Nos. 4,758,357 and 4,615,740, respectively. 
     The optimized formulations in Table 4 have been shown to be stable for at least four months. They did not settle or pack after static aging at ambient temperature during that time. While there was some liquid/solids separation, the separation was not sufficient to warrant further refinement of these new and improved compositions. 
     There are limitations associated with non-oil, hydrophilic solvent based systems for hydroxyethyl cellulose. Hydrophilic solvents tend to hydrate and swell the HEC excessively. This limits the solids content if pourability is desirable. In hydrophilic solvent systems where hydration and swelling are minimal or absent, suspension of the HEC in the solvent becomes a problem. An effective suspension agent added to the solvent should be acid soluble, compatible with the solvent and must not interfere with dispersion or yielding of the HEC. It is also desirable that all components of the formulation be of low toxicity. 
     An advantage of propylene glycol polyols is that they are less toxic than ethylene glycol polyols. Polyether polyols which are propylene glycol based, ranging in molecular weight from 260 to 6000, may be used in the compositions of the present invention. Two polyols, ARCOL PPG-425 and ARCOL LG-650, were employed in these tests. These polyols are soluble in water and, most importantly, infinitely soluble in seawater. 
     ARCOL PPG-425 is a 425 molecular weight polypropylene glycol. It is a propylene oxide adduct of diol starters. It has an average hydroxyl number of 263 and viscosity of 71 cps at 25° C. ARCOL LG-650 is a polyoxypropylene polyol. It is a propylene oxide adduct of triol starters. It has a molecular weight of 260, viscosity at 25° C. is 1059, and the average hydroxyl number is 650. These polyols are available from Arco Chemical Co., Inc. 
     The chemical structures for the chosen polyols are shown below: ##STR5## 
     To determine the swelling effect of the polyols on HEC, one gram of HEC was combined with 9 grams of polyol. The HEC was thoroughly wetted with polyol and placed in a small glass vial. A sample of HEC and propylene glycol was also prepared for comparison, and the samples were examined after 24 hours. For each of the polyol samples, the HEC had settled and the liquid phase was clear. Comparing the polyols, the PPG-425 showed no noticeable swelling affect on the HEC, whereas the LG-650 caused the HEC to swell to more than double the volume the HEC occupied before hydration. The propylene glycol comparison sample had completely hydrated the HEC, to the extent that the HEC appeared to be partially solubilized. No free liquid was observed. 
     Initial samples were prepared using LG-650 and PPG-425 to develop a baseline understanding of how the polyols affected the HEC both separately, in combination and with water. Table 5 lists the formulations and observations of physical appearance. All samples were prepared as weight percent. The HEC content was set at 40 percent using Aqualon HEC 250 HHR. 
     Consistency was graded as thin, medium, medium-thick, thick and very thick. Pourability was graded as pourable, pourable (if stirred), marginally pourable (marginal) and not pourable (not). Syneresis refers to the amount of liquid/solid separation that occurs. 
     
                                           TABLE 5__________________________________________________________________________Initial Samples and Physical AppearanceSample #  1    2    3    4    5    6    7__________________________________________________________________________PPG-425  --   60   55   55   55   50   52  LG-650 60 --  5 --  3  5  5  Water -- -- --  5  2  5  3  HEC 250HHR 40 40 40 40 40 40 40Observations after initial mixConsistency  vry thick       medium            medium                 vry thick                      medium                           vry thick                                med thick  Pourability marginal pourable pourable pourable pourable marginal                                pourableObservations after setting 24 hoursConsistency  solidified       settled            medium                 vry thick                      medium                           vry thick                                med thick  Pourability not if stirred if stirred marginal pourable marginal                                pourable  Syneresis none 50% 30% 10% 20% 5% 5%__________________________________________________________________________ 
    
     Samples with LG-650 greater than 5 percent (except for the sample at 60 percent) were not included in the above table because the resultant mixes were too thick for practical mixing in a plant situation. The appearance of samples 1 and 2 was as expected, based on the preliminary swelling tests. Sample 1 was initially marginally pourable, but solidified after setting for a few hours. When water at 5 percent was blended with PPG-425, the HEC was unevenly hydrated, producing a lumpy, grainy, non-homogeneous mixture. When LG-650 and water were mixed together, the rapid uneven hydration produced by water alone was not evident. Mixtures were evenly hydrated, producing smooth non-lumpy slurries. It appeared that the LG-650 prepared the HEC so that the water evenly hydrated the polymer surface. Water combined with LG-650 also reduced the degree of syneresis. 
     Samples 3 through 7 were tested in brines comprising 10 lb/gal sodium chloride and 11.6 lb/gal calcium chloride to determine their yield times under minimum shear conditions. A LIQUI-VIS sample was also tested for comparison. The test samples were added to brine while mixing at 600 RPM on a Fann® 35A rheometer. Fann is a registered trademark of Fann Instruments, Inc. Apparent viscosity was recorded at 30 minute intervals. The samples were then rolled overnight at 150° F. to determine their ultimate viscosity. Each sample was tested at 2 lb/bbl active polymer. Results are recorded in Tables 6 and 7. 
     
                       TABLE 6______________________________________Viscosification of 10 lb/gal Sodium Chloride  Using a Fann 35A Rheometer at 600 RPM  Reading in Apparent Viscosity, cp  Stir time at 600 RPM           LIQUI-VIS #3   #4   #5   #6   #7______________________________________0 min       2         2      2    2    2    2  30 min 2.5 2.5 3 3 3 3  60 min 2.5 7 33 22 18 31.5  90 min 3 46 46.5 46 47.5 47  120 min 7.5 47.5 47.5 46 48.5 48.5  After 150° F. 41.5 49.5 48.5 49.5 50 51______________________________________ 
    
     The results presented in Table 6 are a bit surprising. As expected, LIQUI-VIS failed to viscosify the brine after 2 hours of mixing. In sodium chloride brine, the HHR variety of HEC (used in LIQUI-VIS and the polyol samples) required a small amount of caustic (less than 1/4 lb/bbl, not added here) to initiate polymer yield in the absence of heat. What was surprising was that the samples prepared with polyols yielded without the addition of caustic. 
     
                       TABLE 7______________________________________Viscosification of 11.6 lb/gal Calcium Chloride  Using a Fann 35A Rheometer at 600 RPM  Reading in Apparent Viscosity, cp  Stir time at 600  RPM LIQUI-VIS #3 #4 #5 #6 #7______________________________________0 min       8.5       8.5    8.5  8.5  8.5  8.5  30 min 31.5 39 43.5 37.5 44.5 40.5  60 min 50 62 69 57.5 70 68  90 min 64 74 80 72.5 82 80  120 min 73.5 82.5 88 82.5 89.5 88  After 150° F. 109 105 108.5 106.5 105.5 106______________________________________ 
    
     In calcium chloride, the polyol samples viscosify the brine at a slightly faster rate than LIQUI-VIS. It may be that the rate of hydration in LIQUI-VIS is influenced by the time it takes water to displace the oil that coats the polymer. 
     It was suspected there might be some dispersion problems with the polyol samples due to their extreme hydrophilic nature. This was the case in the very thick samples. They did tend to produce a few hydrated gel structures. As expected, sample 4, prepared with water and no LG-650, produced the most hydrated gel cells. Medium thick samples produced a few very small hydrated gel cells and medium consistency samples were, for the most part, free of gel cells. 
     Only one of the formulations was selected for further testing in applicable brines. Sample 7 was selected because of its performance, consistency, pourability and syneresis characteristics. It was compared with LIQUI-VIS in seawater, 11.0 lb/gal potassium bromide and 12.5 lb/gal sodium bromide. Although LIQUI-VIS is not normally used in calcium bromide brines, it was included to see if a polyol based sample would perform to any advantage. Test concentration was 2 lb/bbl active. Results are shown in Table 8. 
     
                                           TABLE 8__________________________________________________________________________Viscosification of Various Brines  Comparison Between Polyol Sample #7 and LIQUI-VIS Seawater        11.0 lb/gal KBr                12.5 lb/gal NaBr                        142.2 lb/gal CaBr.sub.2Stir time    LIQUI-  LIQUI-  LIQUI-  LIQUI-  at 600 RPM #7 VIS #7 VIS #7 VIS #7 VIS__________________________________________________________________________0 min 1  1   1   1   2   2   7   7  30 min 43.5 40 1.5 1.5 30 4.5 7.5 7  60 min 45 42 2.5 1.5 46.5 26.5 9.8 7.5  90 min 45 42.5 22.5 6.5 49.5 42.5 13.5 9  120 min 45 42.5 36.5 37 50.5 45 24 14.5  After 150° F. 44.5 42 39.5 41.5 57.5 55 99 104.5__________________________________________________________________________ 
    
     The data in Table 8 showed the polyol formulation to be equal to or better than LIQUI-VIS in each brine. It is interesting to note that the polyol formulation significantly out-performed LIQUI-VIS in the calcium bromide brine. 
     After the polyol samples had set for approximately one week, an increase in syneresis was observed, together with some settling of the HEC polymer. This problem needed to be addressed. Additionally, the presence of gel cells, i.e., fisheyes, was still a concern. It was also desirable to increase the rate of viscosification, ideally so that at least 80 percent of the hot rolled viscosity would be achieved after 60 minutes of mixing. 
     It was thought that perhaps a propylene glycol ether might perform as a carrier fluid and dispersant in view of the use of ethylene glycol monobutyl ether for a similar purpose in the BROMI-VIS product. Arco can supply several propylene based glycol ethers. Arcosolv TPM is a tripropylene glycol methyl ether that is water soluble, possesses low toxicological properties and has a high flash point. TPM has a very low viscosity, i.e., only 5.6 cps at 25° F. In order to make a formulation capable of suspending the HEC, several changes were made to the basic formulations previously tested. PPG-425 was eliminated and the concentration of LG-650 was greatly increased. Amorphous fused silica (AFS) was also included. 
     
                       TABLE 9______________________________________Modified Polyol Formulation  Containing TPMComposition, % by weight                XLQ-22A______________________________________LG-650           39.25  TPM 20  AFS 0.75  HEC 250HHW 40  Consistency medium-thick  Pourability pourable  Syneresis none______________________________________ 
    
     The formulation was tested in a variety of brines to determine the effect of TPM on dispersibility. The tests were run at 2 lb/bbl active polymer and mixing was performed on a Fann 35A rheometer at 600 RPM. The sample designation was XLQ-22A. The results are presented in Table 10. 
     
                       TABLE 10______________________________________Effect Of TPM On Dispersion And Viscosification In Various Brines *Data Is Apparent Viscosity, cp*  Stir time,                             min at 600 RPM Seawater 10 lb/gal NaCl                            11.6 lb/gal CaCl                            .sub.2______________________________________ 0        1        2           8.5  15 42 47 34.5  30 42 47 55  60 42 48 70  90 42 48 81   120 42 47 87  Rolled 150° F. 41.5 48 111.5______________________________________ 
    
     The data indicates that TPM functions as a highly effective dispersant. In seawater and 10 lb/gal sodium chloride, 100 percent of the hot rolled viscosity was achieved within 15 minutes. In 11.6 lb/gal calcium chloride the viscosification rate was roughly double that seen with previous formulations, achieving 63 percent of hot rolled viscosity after 1 hour and 78 percent after 2 hours. It should be noted that although XLQ-22A was a pourable dispersion immediately after preparation, when allowed to set overnight the sample set up, absorbing all the liquid phase and becoming semi-solid. 
     A new series of samples containing TPM were prepared. In this series, the LG-650 and AFS were altered in an effort to make a more pourable suspension. 
     
                       TABLE 11______________________________________Stability and Pourability of Formulations Containing TPM  Quiescent 24 hrs         XLQ-22B  XLQ-22C  XLQ-22D LXQ-22E______________________________________LG-650    29.25    29.50      29.0    14  TPM 30 30 30 40  AFS 0.75 0.50 1.0 1.0  HEC 250HHW 40 40 40 45  Consistency thin thin thin very thin  Pourability pourable pourable pourable pourable  Syneresis none &lt;2% none none______________________________________ 
    
     Samples 22B, 22C, and 22E started settling after 5 days. Sample 22D looked good at 10 days, but some settling of the HEC was becoming evident. 
     Aqualon hydroxyethyl celluloses are designated with either a W or an R suffix. The R suffix indicates that the HEC has been treated with a dialdehyde, glyoxal. This organic delays the hydration of HEC, so that it will disperse more thoroughly before it begins to hydrate and swell. The W suffix indicates that the HEC has not been treated to delay hydration. 
     The formulations developed in accord with the present invention with R type HEC disperse in all brines and freshwater without fisheye formation. However, in some of the brines, specifically sodium chloride, sodium bromide, potassium chloride and potassium bromide, the rate of viscosification is slow. This slow viscosification can be overcome by adding one-quarter pound per barrel or less of caustic to the brine. On the other hand when the W type HEC is used in these same brines, dispersion is excellent and viscosification is very rapid. In seawater and freshwater, however, the W type HEC does not disperse well. Fisheyes and polymer stringers are evident. A closer look at the dispersion characteristics of type W revealed that dispersion was related to salinity. The salinity of a fluid must be greater than about 40,000 to 50,000 ppm for the W type HEC to disperse without fisheye formation. Because it would be more desirable, and in most cases practical, to add caustic to a brine than to cut sack salt to increase salinity of the fluid, the R type HEC is preferred. 
     Further tests established that amorphous fused silica had a definite affect on return permeability. A sample of XLQ-22D with and without AFS was prepared. The test was run using standard Berea sandstone cores. The results are presented in the single FIGURE. Return permeability was reduced by approximately 32 percent relative to that of the sample without AFS. Thus, it was determined that AFS should not be used in the polyol formulations as a suspending agent. 
     Finally, samples of the most preferred embodiment containing the two polyols, TPM and water were prepared with 35 percent HEC. The formulations with comments and observations of their physical appearance over a 4 week period are summarized in Table 12. 
     
                                           TABLE 12__________________________________________________________________________35% HEC Formulations Containing Polyols and WaterFormulations  XLQ-49A        XLQ-49B               XLQ-48C                      XLQ-49D                             XLQ-49E                                   XLQ-49F__________________________________________________________________________PPG-425  35    33     31     29     25    22  LG-650  5  7  9  9 15 15  Water  5  5  5  7  5  8  TPM 20 20 20 20 20 20  HEC 250HHRX 35 35 35 35 35 35__________________________________________________________________________Quiescent 24 hoursConsistency  thin  thin-medium               thin-medium                      medium medium                                   very thick  Pourability pourable pourable pourable pourable pourable marginal                                    Syneresis 10% 10% 5-10% 5% 5%__________________________________________________________________________                                   5%Quiescent 1 weekSyneresis  15%   15%    &lt;10%   10%    5%    &lt;5%  Comments soft texture, slt. firming of slt. firming of slt. firming of                                   soft texture, no settling                                     no packing consistency consisten                                   cy consistency no settling                                     evident__________________________________________________________________________Quiescent 2 weeksSyneresis  15%   15%    10%    10%    5%    5%  Comments soft texture, firming slt. firming of firming, not no settling                                   no settling   no packing settling consistency packed   evident__________________________________________________________________________Quiescent 3 weeksSyneresis  20%   --     15%    10%    5%    5%  Comments firming slt. -- firm, but not firm, not no settling no                                   settling   packing -- packed packed__________________________________________________________________________Quiescent 3 weeksSyneresis  20%   --     20%    15%    5%    5%  Comments firming packed -- firm, soft firm, not no settling no settling    -- packed packed__________________________________________________________________________ 
    
     The data indicates that samples 49E and 49F, with LG-650 at 15 percent and water between 5 and 8 percent, produce excellent samples with minimal syneresis and no settling at 4 weeks. Sample 49F is very thick, however, and only marginally pourable. 
     The following samples were prepared for use in extended static aging studies. 
     
                       TABLE 13______________________________________15% LG-650 Samples For Extended Aging Study  Quiescent  24 hrs XLQ-53A XLQ-53B XLQ-53C XLQ-53D XLQ-53E______________________________________PPG-425 22       20       18     25     24  LG-650 15 15 15 15 15  Water  8  8  8  5  6  TPM 20 22 24 20 20  250 HHRX 35 35 35 35 35  Consistency very thick very thick thick medium medium                                            thick  Pourability marginal marginal marginal pourable pourable  Syneresis none none none 5% &lt;5%______________________________________ 
    
     Formulation XLQ-53E was prepared with four different HEC types to determine the effect on consistency of the sample as a function of the HEC type. These samples were also static aged for an extended time period. None of the samples in Table 13 exhibited any settling of HEC for the 16 week test period. Samples XLQ-53A through 53C showed no syneresis, while 53D and 53E each had less than 5 percent syneresis. Samples XLQ-53A through 53C remained very thick. They were not free flowing dispersions, but could be made to flow from their containers. Dispersibility and viscosification were not affected by the thickness of the samples. While samples 53D and 53E were also thick, they were pourable after minimal hand mixing to restore their fluid character. 
     Samples were prepared using different HEC polymers. As previously mentioned, type R has been treated with a hydration retarder, type W has not. The X designation refers to grind size. Polymers with the X designation are a finer grind size than those without the designation. 
     
                       TABLE 14______________________________________Effect of HEC Type On Formulation Consistency  All Formulations Same As XLQ-53E Except for HEC Type  Quiescent 24 hrs        XLQ-53E    XLQ-53F                          XLQ-54D  XLQ-54E______________________________________HEC Type 250 HHRX   210 HHR  210 HHW  250 HHW  Consistency medium thick medium medium thick thin  Pourability pourable pourable pourable pourable  Syneresis &lt;5% 5% 5% 10%______________________________________ 
    
     Examination of the four types of HEC in Table 14 showed that 250 HHRX is the polymer of choice. Sample XLQ-53E containing the 250 HHRX remained stable during the 16 week test period. The other HECs were not as stable, exhibiting settling of the HEC after five to seven weeks. It would seem that the finer grind size of the HEC is beneficial with respect to suspension of the polymer. 
     XLQ-53D was examined for viscosification efficiency in several brines. The results are shown in Table 15. 
     
                       TABLE 15______________________________________Viscosification of Various Brines  Using XLQ-53D at 2 lb/bbl Active Polymer  Stir time on                   11.0  12.3  11.6  Fann 35A at Sea- 10 ppg 10% ppg ppg ppg  600 RPM, min water NaCl KCl KBr NaBr CaCl.sub.2______________________________________ 0 min   1       2       1     1     2     8.5  15 min 36.5 43.5 28 35 45 48.5  30 min 36.5 45.5 32.5 35 48 77.5  45 min 36 45 36 35 48.5 88  60 min 36 45 37 35 48.5 91  After rolling 35 43 33 32 50.5 95  150° F.  overnight                                      1  STR6##                                      2  STR7##                                      3  STR8##                                      4  STR9##                                      5  STR10##                                      6  STR11##                                      7  STR12##                                      8  STR13##                                      9  STR14##                                      0  STR15##                                      1  STR16##                                      2  STR17##                                      3  STR18##                                      4  STR19##  0.1 lb/bbl no yes yes yes yes no  caustic added______________________________________ 
    
     Caustic was added to brines prior to addition of the viscosifier where noted. Values are apparent viscosity (cp). For comparison, similar results using LIQUI-VIS NT are shown in Table 16. 
     
                                           TABLE 16__________________________________________________________________________Viscosification of Various Brines  Using LIQUI-VIS NT at 2 lb/bbl Active PolymerStir time on Fann 35A           10 ppg   11.0 ppg                         12.3 ppg                              11.6 ppg  at 600 RPM, min Seawater NaCl 10% KCl KBr NaBr CaCl.sub.2__________________________________________________________________________0 min      1    2   1    1    2    8.5  15 min 35.5 35.5 31 31 35 31  30 min 39 41 35.5 34.5 42.5 47  45 min 40 43.5 36.5 36.5 45.5 59  60 min 40 46 36.5 36.5 47 66  After rolling 150° F. 38 44 35.5 34.5 51.5 103  overnight  % yield, 30 min 102%  93% 100% 100% 82.5% 45.6%  % yield, 60 min 105% 104% 103% 106% 91.2% 64.1%  0.1 lb/bbl caustic added no yes yes yes yes no__________________________________________________________________________ 
    
     The foregoing description of the invention has been directed in primary part to particular preferred embodiments in accord with the requirements of the Patent Statute and for purpose of explanation and illustration only. It will be apparent to those skilled in the art that many modifications and changes in these specifically described compositions may be made without departing from the true scope and spirit of the invention. Therefore, the invention is not restricted to the preferred embodiments described and illustrated but covers all modifications which may fall within the scope of the following claims.