Compositions and method for thickening aqueous brines
This is a continuation of application Ser. No. 146,286, filed May 5, 1980, now U.S. Pat. No. 4,392,964. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to compositions for use as thickening agents in aqueous brine systems and to aqueous well servicing fluids prepared therefrom. 
     Thickened aqueous mediums, particularly those containing oil field brines, are commonly used as well servicing fluids such as 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. It is known to use hydrophilic polymeric materials such as hydroxyethyl cellulose (HEC) as thickening agents for aqueous mediums used in such well servicing fluids. However, HEC is not readily hydrated, solvated or dispersed in certain aqueous systems without elevated temperatures and/or mixing under high shear for extended periods of time. For example, hydroxyethyl cellulose polymers are poorly hydrated, solvated or dispersed in aqueous solutions containing one or more multivalent cation water soluble salts, such as heavy brines having a density greater than about 11.7 ppg which are used in well servicing fluids. In many cases, as for example in workover operations, the equipment available for preparing the well servicing fluids does not readily lend itself to high temperature, high shear mixing. Accordingly, it is usually necessary, if it is desired to use such thickened brines to prepare them off the well site or to circulate the fluid in the hot borehole. 
     SUMMARY OF THE INVENTION 
     It is, therefore, an object of the present invention to provide new, polymeric compositions useful for thickening aqueous mediums, especially heavy brines having a density greater than 11.7 pounds per gallon. 
     A further object of the present invention is to provide an improved, aqueous well servicing fluid. 
     Another object of the present invention is to provide a method of preparing a well servicing fluid. 
     Still another object of the present invention is to provide a liquid polymeric composition which is pourable and pumpable, easily handled and which can be used to form thickened aqueous well servicing fluids under conditions of low shear mixing without the addition of heat. 
     The above and other objects of the present invention will become apparent from the description given herein and the appended claims. 
     In accordance with the present invention there is provided, in one embodiment of the invention, a polymeric composition for use in thickening aqueous brine mediums comprising HEC, a water miscible organic liquid, and an aqueous liquid. 
     In another embodiment of the present invention, the polymeric compositions described above can be admixed with an aqueous medium such as, for example, a heavy brine to produce well servicing fluids, e.g. a workover fluid. 
     In the method of the present invention, the polymeric composition is admixed and added to an aqueous brine to form a well servicing fluid. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The polymeric compositions of the present invention utilize, as a hydrophilic polymer, HEC as the primary component to provide the thickening effect. The HEC polymers are solid, particulate materials which are water soluble or water dispersible and which upon solution or dispersion in an aqueous medium increase the viscosity of the system. HEC polymers are generally high yield, water soluble, non-ionic materials produced by treating cellulose with sodium hydroxide followed by reaction with ethylene oxide. Each anhydroglucose unit in the cellulose molecule has three reactive hydroxy groups. The average number of moles of the ethylene oxide that becomes attached to each anhydroglucose unit in cellulose is called moles of substituent combined. In general, the greater the degree of substitution, the greater the water solubility. In general, it is preferable to use HEC polymers having as high a mole substitution level as possible. 
     Usually, upon the addition of dry, powdered hydrophilic materials, such as HEC, to aqueous mediums such as brines, the polymer particles undergo hydration preventing the interior of the particle from readily hydrating, solvating or otherwise dispersing in the aqueous medium. Accordingly, high shear, long mixing times and/or elevated temperatures must be applied in order to obtain a homogeneous system. It is a feature of the present invention that the polymeric compositions of the present invention readily hydrate, dissolve or disperse in such aqueous mediums at relatively low shear and ambient temperature. 
     Although the amount of HEC in the polymeric composition can vary widely depending on the viscosity of the composition desired, generally the HEC will be present in amounts of from about 3 to about 40% by weight of the composition, preferably from about 10 to about 30% by weight, most preferably from about 15% to about 25% by weight. It is preferred that the polymeric composition be pourable. This can be achieved by adjusting the relative concentrations of the HEC and the aqueous phase. The concentration of the aqueous phase must decrease in order to keep the viscosity constant, and vice versa. 
     In addition to the HEC, the polymeric compositions of the present invention contain a water miscible or soluble organic liquid which has no appreciable swelling effect on the HEC. It has been found preferable to employ organic liquids which have a carbon to oxygen ratio of less than about 6 and more preferably less than about 5, and more preferably in the range from 2 to 4. Also, the water soluble organic liquid is preferably soluble or at least dispersible in an aqueous brine having a density of greater than about 11.7 ppg (pounds per gallon). Non-limiting examples of typical organic liquids include isopropanol, 2-ethoxyethanol, 2-butoxyethanol, 2-isopropoxyethanol, n-butanol, sec-butanol, n-pentanol, and mixtures of the above and similar compounds. Specially preferred as the organic liquid is isopropanol (IPA). The organic liquid will generally be present in the polymeric composition in an amount of at least about 40% by weight and, more preferably, from about 50 to about 70% by weight. A test to determine useful water soluble organic liquids has been devised as follows: one (1) part by weight of HEC is spatulated with two (2) parts by weight of the organic liquid. This mixture is allowed to set for one (1) week at room temperature (72° F.) in a sealed container. Liquids useful in the polymeric compositions of this invention will have free liquid present in the mixture after the one week period. Liquids which swell the HEC appreciably will have no free liquid present and are unsuitable in this invention. However, minor amounts of water soluble organic liquids which have a swelling effect on HEC, such as ethylene glycol and glycerol, may be incorporated into the polymeric compositions. The concentration of such liquids will generally be less than about 20% by weight. 
     The aqueous liquid can be any water based mixture or solution which is compatible with the HEC. Thus, for example, the aqueous liquid can be fresh or pure water, sea water, an acidic solution, a basic solution, an aqueous salt solution, or suspension. Although virtually any inorganic or organic acid can be used if an acidic solution is desired, it is preferable to employ monobasic acids, particularly if the polymeric composition is to be added to aqueous brines containing multivalent cations. Non-limiting examples of suitable acids include hydrochloric acid, nitric acid, formic acid, acetic acid, etc. The basic materials which can be employed can be highly water soluble such as, for example, alkali metal hydroxides such as NaOH and KOH, NH 4  OH and the like or less soluble basic materials such as Ca(OH) 2 , MgO and the like. Preferably, when a basic solution or suspension is employed, the concentration of the dissolved basic materials should be less than about 3.0N. Additionally, any aqueous salt solution can be utilized. Preferably the salt will be chosen from the group consisting of NaCl, KCl, CaCl 2 , CaBr 2 , ZnCl 2 , ZnBr 2 , and mixtures thereof. The amount of the aqueous liquid employed in the polymeric compositions can vary from about 3% by weight to about 40% by weight, preferably from about 10 to about 30% by weight. 
     The presence of bases or salts in the aqueous phase enables larger concentrations of aqueous phase to be incorporated into the polymer compositions. This is desirable from a cost standpoint. These solutions also activate the HEC faster than the use of plain water alone. 
     Additionally, the polymeric compositions may contain suspension additives to reduce syneresis and settling. The suspension additive should be a material which exhibits little or no absorption capacity for the organic liquids or the aqueous liquid and which is, in general, non-reactive with the HEC, the aqueous liquid or the organic liquid. Non-limiting examples of such inert suspension additives include bentonite, fumed silica, and hydrophilic polymers such as hydroxypropyl cellulose. 
     In the preparation of the polymeric composition, it is preferred to mix the HEC and water soluble organic liquid together before adding the aqueous liquid. For HEC which has not been surface treated to retard its hydration in aqueous systems, this is necessary in order to prevent the HEC from lumping. For surface treated HEC, this procedure is necessary when the aqueous phase contains base or high concentrations of certain salts as these aqueous systems enhance the hydration of the polymer. 
     While the polymeric compositions of the present invention are useful as thickeners or suspending agents in suspension fertilizers, liquid pesticides, liquid herbicides, and other aqueous systems which require viscosity enhancement, they are particularly useful in the preparation of well servicing fluids and, more particularly, well servicing fluids made from aqueous brines containing soluble salts such as, for example, a soluble salt of an alkali metal, an alkaline earth metal, a Group Ib metal, a Group IIb metal, as well as water soluble salts of ammonia and other cations. The thickener compositions are particularly useful in the preparation of thickened heavy brines, i.e. aqueous solutions of soluble salts of multivalent cations, e.g. Zn and Ca. 
     The most preferred thickened heavy brines, particularly those used for well servicing fluids, are made from brines having a density greater than about 11.7 pounds per gallon (ppg). Especially preferred heavy brines are those having a density of from about 12.0 to about 19.2 ppg which can comprise water solutions of a salt selected from the group consisting of calcium chloride, calcium bromide, zinc chloride, zinc bromide, and mixtures thereof. 
     It has been found that if the polymeric compositions or thickeners are aged before being added to heavy brines, the hydration rate in such brines is increased. Accordingly, although the polymer compositions or thickeners may be added to the heavy brines within several hours of their preparation and in some cases immediately, longer aging times increase the rate at which the thickeners hydrate in the heavy brines. 
     In formulating well servicing fluids from heavy brines, it is preferred that the polymeric composition be admixed with the aqueous brine so as to provide an HEC concentration in the well servicing fluid of from about 1 to about 3 pounds per barrel (ppb). 
    
    
     To more fully illustrate the present invention, the following non-limiting examples are presented. Unless otherwise indicated, all physical property measurements were made in accordance with testing procedures set forth in STANDARD PROCEDURE FOR TESTING DRILLING FLUID API RP 13B, Seventh Edition, April 1978. 
     EXAMPLE 1 
     The effect of the concentration and composition of the aqueous liquid in the activated polymeric compositions on the rate of viscosity development (polymer hydration) in a 16.0 ppg CaBr 2  /ZnBr 2  brine was investigated. The samples were prepared by mixing the HEC and isopropanol together, adding the aqueous liquid, and mixing to thoroughly wet the HEC. The polymer compositions were evaluated at a concentration of 1.5 ppb HEC in a 16.0 ppg CaBr 2  /ZnBr 2  solution by hand shaking the polymer composition and brine solution together for 30  seconds and stirring the mixture on a Fann V-G meter at 300 rpm. The 300 rpm dial reading was taken after certain time periods and after rolling the brines overnight at 150° F. The data are given in Table 1 below. 
     
                       TABLE 1                                                     
______________________________________                                    
Sample Composition: 20% NATROSOL 250 HHW, Indicated                       
Concentration of Aqueous Phase, Remainder Isopropyl Alcohol               
                1.5 ppb HEC in                                            
Aqueous Liquid  16.0 ppg Brine                                            
               %        300 rpm Reading                                   
                                     Qualitative                          
Sample                                                                    
      NaOH     Aqueous  Mixing Time, Minutes                              
                                     Sample                               
No.   Conc.    Phase    0   30   60  A.R..sup.(1)                         
                                           Viscosity                      
______________________________________                                    
 1    0         5       12  21   28  127   Pourable                       
 2    0        10       15  47   66  128   Pourable                       
 3    0        15       18  55   76  135   Pourable                       
 4    0        20       24  67   84  115   Flowable                       
 4a   0        25        9  15   15   33   Gelled                         
 5    0.1N     15       18  42   65  127   Porable                        
 6    0.1N     20       17  64   88  129   Flowable                       
 7    0.1N     25       19  59   86  114   Gelled                         
 8    0.1N     30       16  39   65  107   Gelled                         
 9     0.25N   15       18  51   68  127   Pourable                       
10     0.25N   20       16  61   83  126   Pourable                       
11     0.25N   25       18  60   84  124   Flowable                       
12     0.25N   30       14  65   92  129   Gelled                         
13    0.5N     15       16  52   70  123   Pourable                       
14    0.5N     20       14  55   75  127   Pourable                       
15    0.5N     25       16  61   85  121   Pourable                       
16    0.5N     30       13  47   71  115   Flowable                       
17    1.0N     15       13  28   38  115   Pourable                       
18    1.0N     20       17  50   67  129   Pourable                       
19    1.0N     25       16  55   78  116   Pourable                       
20    1.0N     30       13  43   62  116   Pourable                       
21    2.0N     25       17  36   45  119   Pourable                       
22    3.0N     25       12  21   27  114   Pourable                       
23    4.0N     25       11  18   25   97   Gelled                         
24    5.0N     25       10  16   24  107   Gelled                         
25    .sup.(2) 20       14  49   72  126   Pourable                       
26    .sup.(3) 20       25  64   84  128   Gelled                         
27    .sup.(4) 20       27  72   89  131   Flowable                       
.sup.(5)                                                                  
      --       --        9  --   --  --     --                            
______________________________________                                    
 .sup.(1) Brine rolled overnight at 150° F.                        
 .sup.(2) 0.25N KOH                                                       
 .sup.(3) 0.93% Ca(OH).sup.2 -                                            
 .sup.(4) 0.5% MgO                                                        
 .sup.(5) Brine solution only, no HEC                                     
 
    
     EXAMPLE 2 
     Ethylene glycol monobutyl ether (Butyl CELLOSOLVE), isopropanol and diesel oil were compared for use in the activated polymer compositions. The samples were prepared and evaluated as in Example 1. The data obtained, presented in Table 2, indicate that the organic liquid must be water soluble as the samples containing diesel oil gave very poor results. The data also indicate that the aqueous phase is necessary for activation of the polymer. 
     
                       TABLE 2                                                     
______________________________________                                    
Sample Composition: 20% HEC as Indicated, Indicated Concentra-            
tion of Aqueous Phase, Remainder is the Indicated Organic Phase           
            Aqueous Phase                                                 
                      1.5 ppb HEC in                                      
                            %     16.0 ppg Brine                          
Sam-                        Aque- 300 rpm Reading                         
ple  HEC     Organic  NaOH  ous   Mixing Time, Minutes                    
No.  Type    Liquid** Conc. Phase 0   30   60  A.R.*                      
______________________________________                                    
1    HHW     EGMBE    0.1N  25    13  43   58  125                        
2    HHW     EGMBE    0.25N 25    17  61   79  128                        
3    HHW     EGMBE    0.25N 30    14  45   62  125                        
4    HHW     EGMBE    1.0N  15    12  25   30  121                        
5    HHW     Diesel   0     25    10  11   11   79                        
6    HHW     Diesel   0.25N 25     9   9    9   61                        
7    HHR     IPA      0     10    13  26   34  118                        
8    HHR     IPA      0     15    17  50   66  124                        
9    HHR     IPA      0     20    18  47   65  128                        
10   HHR     IPA      0.25N 24    15  39   63  116                        
11   HHR     IPA      0.25N 23    15  44   64  121                        
12   HHR     IPA      0.25N 22    15  38   60  123                        
13   HHR     EGMBE    0     15    14  30   39  124                        
14   HHR     EGMBE    0.25N 30    17  37   47  117                        
15   HHR     Diesel   0     25    10  12   11   18                        
16   HHR     Diesel   0.25N 25    23  18   20   80                        
17   HHR     IPA      0      0     9   9    9   80                        
______________________________________                                    
 *Brine rolled overnight at 150° F.                                
 **EGMBE is Ethyleneglycol monobutyl ether; IPA is Isopropyl Alcohol;     
 Diesel is Diesel Oil                                                     
 
    
     EXAMPLE 3 
     The effect of aging of the activated polymer composition on the rate of hydration of the polymer in a heavy brine was investigated. The samples were prepared as in Example 1 and tested as in Example 1 after aging the number of hours indicated in Table 3. One sample was prepared at a temperature of about 150° F. The data obtained indicate that: the sample prepared with isopropyl alcohol required no aging for activation; the sample prepared with ethylene glycol monobutyl ether required 2 hours aging for complete activation; and the sample prepared at 150° F. was &#34;super&#34; activated. 
     
                       TABLE 3                                                     
______________________________________                                    
Sample Composition: 20% HHW, 25% 0.25N NaOH,                              
55% Organic Phase                                                         
Sam-                    1.5 ppb HEC in 16.0 ppg Brine                     
ple  Organic            Aging Time of Sample, Hours                       
No.  Phase    300 rpm   0   1    2   3   4   5    16                      
______________________________________                                    
1    EGMBE    Initial   12  14   21  19  15  20   21                      
              30 Minutes                                                  
                        47  48   75  65  66  68   58                      
              60 Minutes                                                  
                        65  69   90  83  86  83   82                      
              After     --  --   --  --  --  --   133                     
              Rolling                                                     
              at 150° F.                                           
2    IPA      Initial   14  13   18  17  15  18   15                      
              30 Minutes                                                  
                        59  53   60  60  62  58   56                      
              60 Minutes                                                  
                        83  78   83  83  84  80   81                      
              After     --  --   --  --  --  --   121                     
              Rolling                                                     
              at 150° F.                                           
3    IPA*     Initial   19  19   16  20  20  15   --                      
              30 Minutes                                                  
                        68  73   70  72  66  54   --                      
              60 Minutes                                                  
                        96  100  95  91  89  80   --                      
              After     --  --   --  --  --  131  --                      
              Rolling                                                     
              at 150° F.                                           
______________________________________                                    
 *Sample prepared at 180° F.                                       
 
    
     EXAMPLE 4 
     The effect of the water soluble organic liquid in the activated polymer compositions was evaluated. Samples were prepared and evaluated as in Example 1. The data obtained, given in Table 4, indicate that the water soluble organic liquid should have a carbon to oxygen ratio less than about 6, preferably less than about 5. 
     
                       TABLE 4                                                     
______________________________________                                    
Sample Composition: 20% NATROSOL 250 HHW; 25% 0.25N                       
NaOH; 55% Indicated Diluting Agent                                        
                       1.5 ppb HEC in                                     
                       16.0 ppg Brine                                     
                       300 rpm Fann Dial Reading                          
Sample                 Mixing Time, Minutes                               
No.   Diluting Agent   0        30    60                                  
______________________________________                                    
1     Isopropyl alcohol                                                   
                       27       66    93                                  
2     2-ethoxy ethanol 15       48    66                                  
3     2-butoxy ethanol 15       63    84                                  
4     2-isopropoxy ethanol                                                
                       18       63    83                                  
5     n-butanol        15       33    51                                  
6     sec-butanol      12       33    45                                  
7     n-pentanol       12       27    36                                  
8     Mixed C.sub.6 --C.sub.10 alcohols                                   
                       12       18    21                                  
9     66% 2-ethoxy ethanol                                                
                       12       48    67                                  
      34% isopropyl alcohol                                               
10    polyethylene glycol,                                                
                       *        *     *                                   
      1200 m.w.                                                           
______________________________________                                    
 *HEC does not disperse and hydrate                                       
 
    
     EXAMPLE 5 
     Activated polymer compositions of this invention, prepared as in Example 1, were evaluated in several different heavy brines as follows: 
     15.0 ppg--Contains 16.3% CaCl 2 , 43.2% CaBr 2 , 40.5% H 2  O 
     16.0 ppg--Contains 38.7% CaBr 2 , 24.6% ZnBr 2 , 36.7% H 2  O 
     19.2 ppg--Contains 20% CaBr 2 , 57% ZnBr 2 , 23% H 2  O 
     Excellent results were obtained. The data are given in Table 5. 
     
                       TABLE 5                                                     
______________________________________                                    
Sample Composition: 20% HEC as Indicated, 25% 0.25N NaOH,                 
55% Isopropyl Alcohol                                                     
                  1.5 ppb HEC                                             
           Brine  300 rpm Reading                                         
Sample                                                                    
      NATROSOL   Density  Mixing Time, Minutes                            
                                       After                              
No.   Type       ppg.     0    30    60    Rolling                        
______________________________________                                    
1     HHR        15.0     48   148   199   227                            
2     HHR        16.0     22    65    95   132                            
3     HHR        19.2     58   153   206   216                            
4     HHW        15.0     48   155   202   243                            
5     HHW        16.0     26    66    93   131                            
6     HHW        19.2     61   159   197   222                            
______________________________________                                    
 
    
     EXAMPLE 6 
     Activated polymer compositions containing a buffered acidic aqueous liquid were prepared and evaluated as in Example 1. Each sample contained 20% NATROSOL 250 HHW, 25% aqueous liquid, and 55% isopropanol. The buffered acidic solutions were prepared as follows: 10 grams of Na 4  P 2  O 7  10H 2  O were dissolved in 80 grams of water followed by the addition of either hydrochloric acid or acetic anhydride to obtain a pH of 3. The data obtained are as follows: 
     
         ______________________________________                                    
        1.5 ppb HEC in 16.0 ppg Brine                                     
        300 rpm Reading                                                   
Acidic    Mixing Time, Minutes                                            
                             After                                        
Solution  0       30         60    Rolling                                
______________________________________                                    
HCl       24      67         85    132                                    
Acetic    13      44         63    128                                    
______________________________________                                    
 
    
     EXAMPLE 7 
     In this Example, the effect of aging of the hydrated HEC on the activation of the HEC was determined. The data after rolling the brines at 150° F. indicates the viscosity obtained when the HEC is completely hydrated. Comparison of the data at room temperature with the data after rolling at 150° F. therefore indicates the relative activation of the HEC as a function of the concentration of water and as a function of aging (&#34;activation&#34;) time. 
     Samples of the polymeric compositions were prepared and evaluated in the following manner: 
     I. 
     (a) 200 grams of the indicated solution of water in 99.9% isopropanol were mixed with 100 grams of HHR for 5 minutes on a Multimixer; 
     (b) 4.5 grams of each was mixed in 350 milliliters of each of the following brines for 5 minutes on a Multimixer: 
     (1) 11.6 ppg CaCl 2  --37.6% CaCl 2   
     (2) 14.2 ppg CaBr 2  --53% CaBr 2   
     (3) 16.0 ppg CaBr 2  /ZnBr 2  --38.7% CaBr 2  +24.6% ZnBr 2   
     (4) 19.2 ppg CaBr 2  /ZnBr 2  --20% CaBr 2  +57% ZnBr 2  ; 
     (c) The brines were placed on a Fann V-G Meter at 300 rpm and 600 and 300 rpm readings were obtained after 30 minutes and 60 minutes; 
     (d) The brines were rolled at room temperature for 3 hours and the 600 and 300 rpm viscosities obtained; 
     (e) The brines were rolled for 16 hours at 150° F., cooled to room temperature, and the viscosities were obtained. 
     II. The composition prepared in Ia was aged for 2 hours at room temperature and evaluated as in steps Ib-Ie. 
     III. The composition prepared in Ia was aged for 4 hours at room temperature and evaluated as in steps Ib-Ie. 
     
                                           TABLE 6                                 
__________________________________________________________________________
Aging                                                                     
Time of  *     Apparent Viscosity of 1.5 ppb HHR in Brine**               
Gellant                                                                   
     Brine                                                                
         Brine % Deionized Water in 99.9% Isopropanol in the Composition  
Hr.  ppg.                                                                 
         Treatment                                                        
               0  1  2  3  4  5  6  10 15 20                              
__________________________________________________________________________
0    11.6                                                                 
         R.T.  50 67 51 71 (73)                                           
                              72 (67)                                     
                                    71 71 79                              
2    11.6                                                                 
         R.T.  68 71 74 64 (79)                                           
                              61 71 64 71 73                              
4    11.6                                                                 
         R.T.  71 65 68 (68)                                              
                           (73)                                           
                              66 72 67 71 79                              
0    11.6                                                                 
         150° F.                                                   
               72 84 72 78 (88)                                           
                              75 (74)                                     
                                    76 78 85                              
2    11.6                                                                 
         150° F.                                                   
               84 81 82 75 (75)                                           
                              81 84 81 79 77                              
4    11.6                                                                 
         150° F.                                                   
               82 81 83 74 (73)                                           
                              84 80 77 77 82                              
0    14.2                                                                 
         R.T.  25 29 28 32 31 40 51 66 64 64                              
2    14.2                                                                 
         R.T.  36 42 46 60 63 60 62 64 63 70                              
4    14.2                                                                 
         R.T.  44 56 57 66 65 53 (66)                                     
                                    70 72 74                              
0    14.2                                                                 
         150° F.                                                   
               78 86 78 80 72 82 88 80 81 81                              
2    14.2                                                                 
         150° F.                                                   
               83 82 79 86 71 82 84 81 75 79                              
4    14.2                                                                 
         150° F.                                                   
               85 84 84 88 77 71 (80)                                     
                                    83 82 85                              
0    16.0                                                                 
         R.T.   8  8  8  8  8  9 13 12 17 24                              
2    16.0                                                                 
         R.T.   8  9  8  9 11 11 18 17 (27)                               
                                          46                              
4    16.0                                                                 
         R.T.   9 10  9 10 11 13 (13)                                     
                                    22 (38)                               
                                          53                              
0    16.0                                                                 
         150° F.                                                   
               78 67 64 68 74 80 72 76 78 62                              
2    16.0                                                                 
         150° F.                                                   
               73 67 76 67 72 87 85 85 (84)                               
                                          82                              
4    16.0                                                                 
         150° F.                                                   
               77 82 76 77 82 88 (76)                                     
                                    88 (86)                               
                                          87                              
0    19.2                                                                 
         R.T.  25 32 30 34 34 42 49 58 55 64                              
2    19.2                                                                 
         R.T.  43 44 54 47 52 58 60 70 85 96                              
4    19.2                                                                 
         R.T.  46 50 55 52 54 59 62 79 83 108                             
0    19.2                                                                 
         150° F.                                                   
               114                                                        
                  105                                                     
                     125                                                  
                        101                                               
                           125                                            
                              OS OS 149                                   
                                       140                                
                                          129                             
2    19.2                                                                 
         150° F.                                                   
               OS 139                                                     
                     132                                                  
                        129                                               
                           121                                            
                              148                                         
                                 OS 132                                   
                                       143                                
                                          138                             
4    19.2                                                                 
         150° F.                                                   
               146                                                        
                  127                                                     
                     130                                                  
                        143                                               
                           126                                            
                              149                                         
                                 148                                      
                                    134                                   
                                       147                                
                                          146                             
__________________________________________________________________________
 *R.T. = After mixing brine 60 minutes at 300 rpm at 74° F.        
 150° F. = After rolling brine for 16 hours at 150° F.      
 **Data in parentheses are the averages of two separate sample            
 determinations                                                           
 
    
     
                       TABLE 7                                                     
______________________________________                                    
1.5 ppb HHR in 11.6 ppg Solution*                                         
% Deionized Water in Isopropanol (99.9%)                                  
0         1      2     3    4    5   6    10  15   20                     
______________________________________                                    
NON-AGED SAMPLE                                                           
30 Minutes                                                                
A.V.    44    59     52  65   (66) 66  (64) 69  65   76                   
P.V.    32    40     37  46   (48) 50  (46) 49  50   58                   
Y.P.    24    39     31  38   (38) 32  (36) 40  31   36                   
60 Minutes                                                                
A.V.    50    67     61  71   (73) 72  (67) 71  71   79                   
P.V.    32    46     40  51   (47) 53  (43) 45  49   56                   
Y.P.    36    43     42  41   (52) 38  (48) 52  44   47                   
4 Hours                                                                   
A.V.    60    74     66  74   (81) 68  (72) 76  70   81                   
P.V.    43    42     41  41   (45) 39  (43) 41  41   52                   
Y.P.    35    64     50  66   (72) 59  (59) 70  59   59                   
16 Hours at                                                               
150° F.                                                            
A.V.    72    84     72  78   (88) 75  (74) 76  78   85                   
P.V.    42    47     40  42   (46) 43  (43) 42  44   46                   
Y.P.    61    74     64  71   (83) 64  (63) 68  68   78                   
SAMPLE AGED 2 HOURS AT ROOM TEMPERATURE                                   
30 Minutes                                                                
A.V.    59    64     71  58   (70) 63  68   62  68   70                   
P.V.    39    51     53  40   (48) 48  52   46  49   53                   
Y.P.    41    26     36  37   (45) 30  32   32  38   35                   
60 Minutes                                                                
A.V.    68    71     74  64   (79) 67  71   64  71   73                   
P.V.    49    54     49  44   (52) 49  50   44  46   49                   
Y.P.    38    34     50  41   (55) 37  43   41  50   48                   
4 Hours                                                                   
A.V.    74    72     74  67   (79) 66  69   74  73   77                   
P.V.    45    41     42  41   (44) 38  40   44  40   44                   
Y.P.    58    62     64  53   (69) 57  59   60  67   67                   
16 Hours at                                                               
150° F.                                                            
A.V.    84    81     82  75   (75) 81  84   81  79   77                   
P.V.    46    46     46  42   (42) 45  46   45  44   43                   
Y.P.    77    71     72  66   (65) 72  76   73  70   69                   
SAMPLE AGED 4 HOURS AT ROOM TEMPERATURE                                   
 30 Minutes                                                               
A.V.    66    60     64  (64) (68) 64  68   66  68   75                   
P.V.    46    45     49  (46) (51) 47  51   48  51   60                   
Y.P.    40    31     30  (35) (36) 35  34   37  34   31                   
60 Minutes                                                                
A.V.    71    65     68  (68) (73) 66  72   67  71   79                   
P.V.    51    46     49  (46) (51) 44  50   42  53   58                   
Y.P.    40    39     39  (44) (44) 45  44   50  37   42                   
4 Hours                                                                   
A.V.    73    71     70  75   (75) 73  70   72  72   80                   
P.V.    43    44     40  43   (45) 43  40   41  42   46                   
Y.P.    60    54     61  64   (62) 60  60   62  61   69                   
16 Hours at                                                               
150° F.                                                            
A.V.    82    81     83  74   (73) 84  80   77  77   82                   
P.V.    46    46     47  42   (41) 47  46   43  42   45                   
Y.P.    72    71     73  64   (62) 74  69   69  71   75                   
______________________________________                                    
 *Data in parentheses are the average of two separate sample determination
 
    
     
                       TABLE 8                                                     
______________________________________                                    
          1.5 ppb HHR in 14.2 ppg Solution*                               
          % Deionized Water in Isopropanol (99.9%)                        
          0   1     2     3   4   5   6    10  15  20                     
______________________________________                                    
NON-AGED SAMPLE                                                           
30 Minutes                                                                
A.V.        21    25    26  29  28  36  48   67  61  60                   
P.V.        18    20    20  27  22  25  31   28  41  37                   
Y.P.         6    11    12   5  13  22  34   78  40  46                   
60 Minutes                                                                
A.V.        25    29    28  32  31  40  51   66  64  64                   
P.V.        20    21    21  23  23  27  33   30  40  39                   
Y.P.        11    16    15  19  17  26  37   73  48  50                   
4 Hours                                                                   
A.V.        34    38    35  40  38  45  54   60  67  67                   
P.V.        24    25    24  27  25  29  37   34  37  39                   
Y.P.        21    26    23  27  26  32  34   52  60  56                   
16 Hours at 150° F.                                                
A.V.        78    86    78  80  72  82  88   80  81  81                   
P.V.        41    43    41  41  37  42  45   42  40  41                   
Y.P.        75    86    75  78  70  81  88   76  82  81                   
SAMPLE AGED 2 HOURS AT ROOM TEMPERATURE                                   
30 Minutes                                                                
A.V.        33    39    41  56  58  56  58   61 60   67                   
P.V.        23    26    28  35  41  38  38   38 37   45                   
Y.P.        20    26    26  42  35  37  40   46 46   45                   
60 Minutes                                                                
A.V.        36    42    46  60  63  60  62   64 63   70                   
P.V.        24    28    30  38  42  40  40   39 40   44                   
Y.P.        25    29    32  45  42  41  44   50 46   53                   
4 Hours                                                                   
A.V.        45    49    51  67  66  62  66   67 65   72                   
P.V.        28    31    31  38  37  35  37   37 36   37                   
Y.P.        34    37    40  59  59  54  59   61 58   71                   
16 Hours at 150° F.                                                
A.V.        83    82    79  86  71  82  84   81 75   79                   
P.V.        43    42    42  42  36  43  43   41 39   41                   
Y.P.        80    81    74  88  71  79  82   81 73   76                   
SAMPLE AGED 4 HOURS AT ROOM TEMPERATURE                                   
30 Minutes                                                                
A.V.        40    51    53  60  60  49  (60) 67 70   72                   
P.V.        27    31    33  37  39  30  (38) 45 44   47                   
Y.P.        27    41    40  47  43  39  (44) 45 53   51                   
60 Minutes                                                                
A.V.        44    56    57  66  65  53  (66) 70 72   74                   
P.V.        29    34    35  41  41  33  (44) 44 42   43                   
Y.P.        31    44    44  50  48  41  (44) 53 61   62                   
4 Hours                                                                   
A.V.        52    58    60  68  69  56  (67) 74 74   77                   
P.V.        31    34    33  37  38  34  (37) 40 38   39                   
Y.P.        42    48    55  63  62  44  (60) 68 72   77                   
16 Hours at 150° F.                                                
A.V.        85    84    84  88  77  71  (80) 83 82   85                   
P.V.        44    43    43  43  38  39  (42) 43 41   42                   
Y.P.        82    83    83  90  79  64  (77) 81 82   87                   
______________________________________                                    
 *Data in parentheses are the average of two separate sample determination
 
    
     
                                           TABLE 9                                 
__________________________________________________________________________
          1.5 ppb HHR in 16.0 ppg Solution*                               
          % Deionized Water in Isopropanol (99.9%)                        
          0   1   2   3  4 5  6  10 15 20                                 
__________________________________________________________________________
NON-AGED SAMPLE                                                           
30 Minutes                                                                
A.V.      8   8   8    8  8                                               
                            8 12 11 15 21                                 
P.V.      9   8   8    8  8                                               
                            9 12 12 15 19                                 
Y.P.      -1  0   0    1  1                                               
                           -1  0 -1  1  4                                 
60 Minutes                                                                
A.V.      8   8   8    8  8                                               
                            9 13 12 17 24                                 
P.V.      9   8   8    8  8                                               
                            9 13 12 16 20                                 
Y.P.      -1  0   1    1  1                                               
                            0  0  0  3  9                                 
4 Hours                                                                   
A.V.      8   8   8    8  9                                               
                           10 14 14 20 39                                 
P.V.      8   9   9    8  9                                               
                           11 14 13 17 26                                 
Y.P.      1   - 1 -1   1  0                                               
                           -1  1  3  6 26                                 
16 Hours at 150° F.                                                
A.V.      78  67  64  68 74                                               
                           80 72 76 78 62                                 
P.V.      40  38  39  39 38                                               
                           43 40 43 43 41                                 
Y.P.      56  58  51  58 73                                               
                           75 64 66 71 81                                 
SAMPLE AGED 2 HOURS AT ROOM TEMPERATURE                                   
30 Minutes                                                                
A.V.      8   9   8    8 10                                               
                           10 17 16 (22)                                  
                                       42                                 
P.V.      8   9   8    9 10                                               
                           11 16 15 (19)                                  
                                       31                                 
Y.P.      1   0   0   -1  0                                               
                           -1  2  2  (6)                                  
                                       22                                 
60 Minutes                                                                
A.V.      8   9   8    9 11                                               
                           11 18 17 (27)                                  
                                       46                                 
P.V.      8   9   8    9 11                                               
                           11 17 15 (21)                                  
                                       30                                 
Y.P.      1   1   1    0  0                                               
                            1  4  5 (12)                                  
                                       32                                 
4 Hours                                                                   
A.V.      10  9   9   11 13                                               
                           15 22 22 (33)                                  
                                       44                                 
P.V.      10  9   9   12 12                                               
                           14 18 17 (24)                                  
                                       32                                 
Y.P.      0   1   1   -1  2                                               
                            2  9 10 (19)                                  
                                       24                                 
16 Hours at 150° F.                                                
A.V.      73  67  76  67 72                                               
                           87 85 85 (84)                                  
                                       82                                 
P.V.      41  39  44  37 38                                               
                           47 42 45 (45)                                  
                                       44                                 
Y.P.      65  57  64  60 69                                               
                           80 86 81 (78)                                  
                                       76                                 
SAMPLE AGED 4 HOURS AT ROOM TEMPERATURE                                   
30 Minutes                                                                
A.V.      8   9   9    9 10                                               
                           11 (12)                                        
                                 20 (33)                                  
                                       44                                 
P.V.      8   9   9   10 10                                               
                           12 (12)                                        
                                 18 (25)                                  
                                       33                                 
Y.P.      1   1   0   -1  0                                               
                           -1  (0)                                        
                                  4 (15)                                  
                                       23                                 
60 Minutes                                                                
A.V.      9   10  9   10 11                                               
                           13 (13)                                        
                                 22 (38)                                  
                                       53                                 
P.V.      9   10  10  11 11                                               
                           13 (13)                                        
                                 19 (28)                                  
                                       36                                 
Y.P.      0   0   -1  -1  0                                               
                            0  (0)                                        
                                  6 (22)                                  
                                       35                                 
4 Hours                                                                   
A.V.      11  11  12  12 13                                               
                           16 (16)                                        
                                 25 (46)                                  
                                       51                                 
P.V.      11  10  12  12 12                                               
                           15 (14)                                        
                                 19 (31)                                  
                                       34                                 
Y.P.      0   2   1    0  2                                               
                            2  (4)                                        
                                 14 (30)                                  
                                       34                                 
16 Hours at 150° F.                                                
A.V.      77  82  76  77 82                                               
                           88 (76)                                        
                                 88 (90)                                  
                                       87                                 
P.V.      42  42  43  38 41                                               
                           45 (43)                                        
                                 48 (47)                                  
                                       45                                 
Y.P.      71  80  67  58 82                                               
                           87 (66)                                        
                                 81 (87)                                  
                                       85                                 
__________________________________________________________________________
 *Data in parentheses are the average of two separate sample determination
 
    
     
                                           TABLE 10                                
__________________________________________________________________________
          1.5 ppb HHR in 19.2 ppg Solution*                               
          % Deionized Water in Isopropanol (99.9%)                        
          0  1  2  3  4  5  6  10 15 20                                   
__________________________________________________________________________
NON-AGED SAMPLE                                                           
30 Minutes                                                                
A.V.      21 25 23 26 27 30 33 38 36 42                                   
P.V.      22 26 24 27 27 31 33 36 37 39                                   
Y.P.      -1 -2 -1 -1  0 -1 31  5 -2  6                                   
60 Minutes                                                                
A.V.      25 32 30 34 39 42 49 58 55 64                                   
P.V.      25 31 29 31 32 37 44 48 48 50                                   
Y.P.       1  2  2  7  5 10 11 21 14 29                                   
4 Hours                                                                   
A.V.      41 54 49 53 56 60 79 87 92 95                                   
P.V.      34 43 39 42 43 47 57 59 64 62                                   
Y.P.      14 23 21 23 26 27 45 57 57 67                                   
16 Hours at 150° F.                                                
A.V.      114                                                             
             105                                                          
                125                                                       
                   101                                                    
                      125                                                 
                         OS OS 149                                        
                                  140                                     
                                     129                                  
P.V.      75 67 74 69 74 OS OS 90 83 69                                   
Y.P.      79 75 102                                                       
                   64 103                                                 
                         OS OS 118                                        
                                  115                                     
                                     120                                  
SAMPLE AGED 2 HOURS AT ROOM TEMPERATURE                                   
30 Minutes                                                                
A.V.      30 32 34 32 34 40 41 47 57 68                                   
P.V.      31 33 33 33 34 38 42 44 54 55                                   
Y.P.      -1 -2  2 -1  0  5 -1  7  6 26                                   
60 Minutes                                                                
A.V.      43 44 54 47 52 58 60 70 85 96                                   
P.V.      38 42 45 46 46 49 51 54 66 69                                   
Y.P.      10  5 18  2 13 19 19 32 38 54                                   
4 Hours                                                                   
A.V.      68 70 82 81 87 91 99 95 110                                     
                                     113                                  
P.V.      51 54 56 59 62 61 65 65 70 69                                   
Y.P.      35 33 52 44 50 61 68 61 80 89                                   
16 Hours at 150° F.                                                
A.V.      OS 139                                                          
                132                                                       
                   129                                                    
                      121                                                 
                         148                                              
                            OS 132                                        
                                  143                                     
                                     138                                  
P.V.      OS 84 76 77 72 90 OS 79 85 78                                   
Y.P.      OS 110                                                          
                113                                                       
                   103                                                    
                      99 116                                              
                            OS 106                                        
                                  116                                     
                                     121                                  
SAMPLE AGED 4 HOURS AT ROOM TEMPERATURE                                   
30 Minutes                                                                
A.V.      32 34 35 37 35 38 41 55 58 75                                   
P.V.      31 33 34 37 35 37 39 49 52 59                                   
Y.P.       3  3  2  0  0  3  5 13 12 32                                   
60 Minutes                                                                
A.V.      46 50 55 52 54 59 62 79 83 108                                  
P.V.      41 42 45 47 46 40 50 61 64 80                                   
Y.P.      10 16 20 11 16 28 24 37 39 56                                   
4 Hours                                                                   
A.V.      74 79 90 85 90 91 92 102                                        
                                  111                                     
                                     125                                  
P.V.      54 55 64 61 63 64 61 67 71 75                                   
Y.P.      40 49 52 49 55 54 62 70 81 101                                  
16 Hours at 150° F.                                                
A.V.      146                                                             
             127                                                          
                130                                                       
                   143                                                    
                      126                                                 
                         149                                              
                            148                                           
                               134                                        
                                  147                                     
                                     146                                  
P.V.      88 73 76 85 73 91 90 84 84 81                                   
Y.P.      113                                                             
             108                                                          
                108                                                       
                   116                                                    
                      106                                                 
                         116                                              
                            107                                           
                               101                                        
                                  126                                     
                                     130                                  
__________________________________________________________________________
 *Data in parentheses are the average of two separate sample determination
                                                                          
 
    
     The data in Table 6 summarize the data in Tables 7-10. The data indicate generally that: (1) brines having a density greater than 11.6 ppg require activation of the HEC; (2) the larger the concentration of water, the greater the activation of the HEC (subject to the limitation of forming a gel which does not disperse at low shear); and (3) the activation increases as the composition ages. 
     EXAMPLE 8 
     To 175 grams of ethylene glycol mono-n-butyl ether (EGMBE) were added 92.3 grams of water and 57.7 grams of 78% CaCl 2 . After mixing for 2 minutes with a MultiMixer, 75 grams of NATROSOL 250 HHR was added. The mixture immediately thickened. While stirring with a variable speed LIGHTNIN mixer, an additional 50 grams of EGMBE was added to give a final concentration of HEC of 162/3% by weight. A sample of a 16.0 ppg CaBr 2  /ZnBr 2  solution containing 1 ppb HEC was prepared by hand shaking together 350 ml of a salt solution and 6 grams of the EGMBE-HEC thickener and stirring the mixture on a Fann V-G meter at 300 rpm. The 300 rpm dial reading was taken after certain time periods shown in Table 13 below. The API rheology was obtained on the viscosified brine after 60 minutes at 300 rpm after rolling the brine overnight at 150° F. The data obtained are given in Table 11 below. 
     
                       TABLE 11                                                    
______________________________________                                    
               Fann V-G Meter                                             
               300 rpm Dial Reading                                       
______________________________________                                    
Minutes @ 300 rpm                                                         
 0               9                                                        
10               18                                                       
20               25                                                       
30               33                                                       
60               51                                                       
After Rolling    74                                                       
API Rheology                                                              
After 60 Minutes                                                          
AV               41                                                       
PV               31                                                       
YP               20                                                       
After Rolling at 150° F.                                           
AV               53.5                                                     
PV               33                                                       
YP               41                                                       
______________________________________                                    
 
    
     EXAMPLE 9 
     Samples of thickeners prepared using various salt solutions as the aqueous liquid and having the following compositions were prepared by mixing together NATROSOL 250 HHR and isopropanol followed by the addition of the aqueous salt solution: 
     
         ______________________________________                                    
Sample                                                                    
      %      %       %                                                    
No.   HEC    IPA     Aqueous                                              
                            Aqueous Phase                                 
______________________________________                                    
A     20     55      25     10.0 ppg NaCl (26% NaCl)                      
B     20     55      25     11.6 ppg CaCl.sub.2 (37.6% CaCl.sub.2)        
C     20     50      30     14.2 ppg CaBr.sub.2 (53% CaBr.sub.2)          
D     20     40      40     19.2 ppg ZnBr.sub.2 /CaBr.sub.2               
                            (57% ZnBr.sub.2, 20% CaBr.sub.2)              
______________________________________                                    
 
    
     The above samples were evaluated as heavy brine viscosifiers using a 19.2 ppg (pounds per gallon) ZnBr 2  /CaBr 2  solution as follows: 7.5 ppb of each sample (1.5 ppb (pounds per barrel) HEC) were mixed with the 19.2 ppg salt solution for 15 minutes on a MultiMixer. Thereafter, the brines were statically aged for 1 hour before obtaining the API rheology. The samples were rolled at 150° F. for 16 hours and the API rheology obtained after the samples cooled to room temperature. The data obtained are given in Table 12 below. 
     
                       TABLE 12                                                    
______________________________________                                    
API Rheology                                                              
Room Temperature   16 Hours @ 150° F.                              
Sample 600     300      3    600     300   3                              
______________________________________                                    
A      265     182      27   &gt;300    218   40                             
B      245     161      20   &gt;300    209   36                             
C      259     175      24   &gt;300    213   38                             
D      236     161      21    289    200   34                             
______________________________________                                    
 
    
     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalence of the claims are therefore intended to be embraced therein.