Abstract:
A thickened brine solution useful as a well servicing fluid is prepared, said solution consisting essentially of water, at least 20% by weight zinc bromide, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to thickened brine solutions and, more particularly, to so called heavy brines having a density of about 14.2 pounds per gallon (ppg) or greater. 
     Hydroxyethyl cellulose (HEC) is used as a viscosifyer in aqueous solutions containing dissolved salt. Being non-ionic, it is one of the few materials which will hydrate in and efficiently viscosify heavy brine solutions of the type used as well servicing fluids, e.g. in workover and completion operations. 
     Heavy brine solutions having a density greater then about 15.0 ppg contain a soluble salt having a density greater than the density of calcium bromide. Usually, zinc chloride and/or zinc bromide is used, preferably zinc bromide. It is sometimes necessary to utilize a brine solution having a density in the range of about 14.2 ppg to about 15.0 ppg which has a lower temperature of crystallization than a similar density solution containing calcium chloride and calcium bromide. Such a solution can be formulated, from a density standpoint, using zinc bromide. However, we have found that if the zinc bromide concentration is less than about 20% by weight, the HEC will not gel or thicken the brine. Indeed, we have found that while it is possible to viscosify a brine solution containing no zinc bromide or a brine solution containing a high concentration of zinc bromide, if the two thickened solutions are admixed to produce a solution containing zinc bromide in less than about a 20% by weight concentration, the viscosity of the mixed brine will be essentially the same as if no HEC is present. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide thickened brine solutions containing zinc bromide and HEC. 
     Another object of the present invention is to provide a method for preparing such thickened brines. 
     The above and other objects of the present invention will become apparent from the description given herein and the appended claims. 
     In one embodiment, the present invention provides a thickened brine consisting essentially of water, at least 20% by weight zinc bromide, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose. 
     In another embodiment, the present invention provides a method of preparing thickened brines in which an aqueous solution consisting essentially of water, at least 20% by weight zinc bromide and calcium bromide is admixed with a viscosifying amount of hydroxyethyl cellulose. 
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention is based on the discovery that if the zinc bromide concentration in a brine solution is kept at at least about 20% or greater by weight, the brine can be thickened or gelled with hydroxyethyl cellulose. Thus, brine solutions of widely varying densities containing zinc bromide, calcium bromide and/or calcium chloride can be formulated. 
     The HEC polymers which are useful in the present invention, depending upon the method of preparation of the thickened brines, can either be in the form of a dry powder, essentially untreated, or, in the preferred case, can be an &#34;activated&#34; HEC. The term activated as used herein refers to an HEC polymer which will substantially hydrate or solubilize in a brine solution having a density greater than about 14.2 pounds per gallon (ppg) without the necessity for mixing, as by rolling, at elevated temperatures. Examples of such activated HEC polymers are to be found in co-pending U.S. Patent applications Ser. Nos. 119,805, filed Feb. 8, 1980, now U.S. Pat. No. 4,330,414 and 146,286, filed May 5, 1980, herein incorporated by referemce for all purposes. As disclosed in the aforementioned patent applications, HEC polymers which have been activated will solubilize in brine solutions without the necessity for rolling, or other forms of mixing at elevated temperatures. In general, any HEC polymer which will solubilize in a brine having a density in excess of about 14.2 ppg at room temperature can be considered an &#34;activated&#34; HEC. It is to be understood, however, that the present invention is not limited to the use of activated HEC polymers. Depending on the condition of mixing, and the composition of the brine, unactivated HEC polymers are compatible with brine solutions used in the present invention. The term &#34;compatible&#34; as used herein means that the HEC polymer can be solvated or solubilized in a given brine solution with the use of mixing techniques such as rolling at elevated temperatures. Thus, an incompatible system is one in which the HEC polymer will not solubilize in the brine regardless of the mixing conditions used. 
     In formulating the brine solutions used in the present invention, zinc bromide, calcium bromide, and, in certain cases, calcium chloride are employed depending upon the desired density and the desired temperature of crystallization of the brine. We have found that the presence or absence of calcium chloride and the desired density of the brine determines the minimum amount of zinc bromide which can be utilized in the brine either to form brines which are compatible with HEC or which can be viscosified with an activated HEC at room temperature. Basically, there exist four cases: 
     CASE 1: Solutions containing zinc bromide and calcium bromide which contain no calcium chloride are compatible with HEC provided that the minimum percent zinc bromide in the brine solution is as follows: 
     
         ______________________________________Solution Density (D), ppg            Minimum % ZnBr.sub.2______________________________________ 14.2-15.63      2015.63-18.0             ##STR1##______________________________________ 
    
     where d is the density (ppg) of a solution mixed with a zinc bromide solution having a density of 19.2 ppg. In instances where another solution containing zinc bromide is used rather than a 19.2 ppg zinc bromide solution, the minimum percent zinc bromide which can be used in a brine having a density of from 15.63 to 18.0 ppg is ##EQU1## where w is the density (ppg) of the zinc bromide solution and p is the percent zinc bromide in that solution. 
     CASE 2: Solutions which contain zinc bromide, calcium bromide and calcium chloride are compatible with HEC provided that the maximum percent calcium chloride in the solution is (2×33) % wherein x is the percent zinc bromide in the solution. In this case, the minimum percent zinc bromide in the solution is as follows: 
     
         ______________________________________Solution Density (D), ppg             Minimum % ZnBr.sub.2______________________________________ 14.2-15.63       2015.63-17.0        8.57D-113.7______________________________________ 
    
     CASE 3: ZnBr 2  /CaBr 2  brine solutions containing no calcium chloride can be gelled or viscosified at room temperature with an activated HEC composition provided that the minimum percent zinc bromide in the solution is as follows: 
     
         ______________________________________Solution Density (D), ppg            Minimum % ZnBr.sub.2______________________________________14.2-15.2        2015.2-16.0        5.75D-67.416.0-18.0             ##STR2##______________________________________ 
    
     where d is the density (ppg) of a solution containing only calcium bromide which is mixed with a 19.2 ppg zinc bromide solution. If another solution containing zinc bromide replaces the 19.2 ppg zinc bromide solution, then the minimum percent zinc bromide in the density range from 16.0 to 18.0 ppg is ##EQU2## where w is the density (ppg) of the zinc bromide solution and p is the percent zinc bromide in the solution 
     CASE 4: ZnBr 2  /CaBr 2  brine solutions containing calcium chloride can be gelled or viscosified at room temperature with an activated HEC composition provided that the maximum weight percent calcium chloride in the solution is (2×33)% where x is the percent zinc bromide in the solution. The minimum percent zinc bromide in the solution is as follows: 
     
         ______________________________________Solution Density (D), ppg             Minimum % ZnBr.sub.2______________________________________14.2-14.5         20 14.5-16.55       4(D-9.5)14.5-17.0         4(D-9) 14.5-17.45       4(D-8.5)______________________________________ 
    
     wherein D is the density of the brine solution in ppg. 
     In formulating the thickened brines of the present invention, the HEC will be present in a viscosifying amount, generally in a concentration of from about 1 to about 5 ppb (pounds per 42 gallon barrel). 
     To more fully illustrate the present invention, the following non-limiting examples are presented. All percentages given in the examples and throughout the specification are by weight unless otherwise indicated. All physical property measurements were made in accordance with testing procedures set forth in Standard Procedure For Testing Drilling Fluids API RP 13B, 7th Edition, April, 1978. The HEC polymer employed, unless otherwise indicated, was an HEC marketed by Hercules, Inc., under the tradename NATROSOL 250 HHR. In formulating the brine solutions, the following salt solutions were employed: 
     
         ______________________________________19.2 ppg solution           aqueous solution containing           20% CaBr.sub.2 and 57% ZnBr.sub.214.2 ppg solution           aqueous solution containing           53% CaBr.sub.211.6 ppg solution           aqueous solution containing           37.6% CaCl.sub.2______________________________________ 
    
    
    
     EXAMPLE 1 
     Various brine solutions were admixed with an activated HEC containing 20% NATROSOL 250 HHR, 25% glycerin, 54.6% isopropanol, and 0.4% fumed silica to produce a final solution containing 3 ppb HEC. The mixing was conducted on a Multimixer for one minute. Thereafter, the rate of hydration of the HEC was measured by stirring the solutions on a Fann-VG-Meter at 300 rpm and periodically reading the dial reading over a 60 minute period. The solutions were then hot rolled overnight at 150° F. to determine the final viscosity. The data obtained are given in Table 1. 
     
                                           TABLE 1__________________________________________________________________________Composition of Solution         3 ppb. NATROSOL 250 HHR            19.2               11.6                   14.2                       95% Fann 300 rpm ReadingDensity%   %   %   ppg               ppg ppg CaCl.sub.2                                After Rollingppg. ZnBr.sub.2    CaCl.sub.2        CaBr.sub.2            bbl.               bbl.                   bbl.                       lb. Initial                                16 Hr. @ 150° F.*__________________________________________________________________________15.0 11.7    0   46.2            0.160               0   0.840                       0   7    1415.1 13.0    0   45.5            0.180               0   0.82                       0   7    2715.3 15.7    0   43.9            0.220               0   0.780                       0   10   3715.5 18.4    0   42.4            0.260               0   0.740                       0   48   22215.8 22.2    0   40.2            0.320               0   0.680                       0   130  OS16.0 24.6    0   38.7            0.360               0   0.640                       0   127  OS16.5 30.5    0   35.3            0.460               0   0.540                       0   154  OS17.0 36.1    0   32.1            0.560               0   0.440                       0   197  OS17.5 41.3    0   29.1            0.660               0   0.340                       0   OS   OS18.0 46.2    0   26.3            0.260               0   0.240                       0   OS   OS18.5 50.9    0   23.6            0.860               0   0.140                       0   OS   OS19.0 55.3    0   21.0            0.960               0   0.040                       0   OS   OS15.0 0   16.3        43.2            0  0.0286                   0.8637                       103.0                           291  OS15.1 1.7 15.8        42.5            0.024               0.028                   0.843                       100.5                           29   2915.3 5.1 14.9        41.1            0.071               0.027                   0.802                       95.7                           29   2415.5 8.4 13.9        39.8            0.119               0.025                   0.761                       90.7                           28   2615.8 13.2    12.5        37.8            0.190               0.023                   0.700                       83.4                           23   2516.0 16.3    11.6        36.6            0.238               0.022                   0.658                       78.5                           25   2416.5 23.7    9.5 33.6            0.357               0.018                   0.555                       66.2                           28   17517.0 30.6    7.5 30.7            0.476               0.015                   0.453                       54.0                           38   16017.5 37.1    5.7 28.1            0.592               0.012                   0.350                       41.7                           75   OS18.0 43.1    3.9 25.5            0.714               0.008                   0.247                       29.5                           158  OS18.5 49.3    2.2 23.1            0.833               0.005                   0.144                       17.2                           OS   OS19.0 54.8    0.6 20.9            0.952               0.0014                   0.0415                       4.9 OS   OS__________________________________________________________________________ *OS = Offscale, &gt;300. 
    
     As can be seen from Table 1, solutions containing less than about 20% ZnBr 2  cannot be efficiently gelled or viscosified even with an activated HEC. 
     EXAMPLE 2 
     Brine solutions having varying densities were formulated using various salt solutions and, in some cases, solid calcium chloride. The brine solutions were mixed on a Multimixer for 5 minutes with an activated HEC containing 20% NATROSOL 250 HHR, 25% 0.25 N sodium hydroxide and 55% isopropanol to form brine solutions having 2 ppb HEC. The solutions were then rolled 55 minutes at room temperature and the Fann 300 rpm readings obtained. Following rolling for 16 hours at 150° F., cooling to room temperature and mixing 5 minutes on a Multimixer, the Fann 300 rpm readings were obtained again. The data are given in Table 2. 
     
                                           TABLE 2__________________________________________________________________________Composition of Solution         2 ppb. NATROSOL 250 HHR            19.2               11.6                   14.2                       95% Fann 300 rpm ReadingDensity%   %   %   ppg               ppg ppg CaCl.sub.2                                After Rollingppg. ZnBr.sub.2    CaCl.sub.2        CaBr.sub.2            bbl.               bbl.                   bbl.                       lb. Initial                                16 Hr. @ 150° F.*__________________________________________________________________________14.5 20  0   36.1            0.265               0   0.561                       0   73   11015.0 20  0   38.5            0.274               0   0.628                       0   75   12515.2 20  0   39.5            0.278               0   0.656                       0   57   13215.4 20  0   40.4            0.281               0   0.683                       0   37   13215.6 20  0   41.3            0.285               0   0.711                       0   33   13815.8 20  0.02        40.9            0.289               0   0.711                       0.16                           31   13816.0 20  0.05        40.3            0.292               0   0.708                       0.35                           30   14214.5 20  18.6        18.8            0.265               0.481                   0.226                       26.7                           10   1615.0 20  16.2        23.8            0.274               0.350                   0.334                       40.1                           13   1915.2 20  15.3        25.7            0.278               0.297                   0.378                       45.3                           14   1915.4 20  14.3        27.6            0.281               0.244                   0.422                       50.5                           17   1915.6 20  13.7        29.5            0.285               0.190                   0.467                       58.0                           17   2115.8 20  12.5        31.3            0.289               0.138                   0.509                       60.9                           20   2116.0 20  11.7        33.1            0.292               0.085                   0.554                       66.1                           20   2514.5 26  0   30.6            0.3445               0   0.413                       0   86   10915.0 26  0   33.0            0.356               0   0.477                       0   93   12215.2 26  0   34.0            0.361               0   0.502                       0   101  12815.4 26  0   34.9            0.366               0   0.527                       0   114  14015.6 26  0   35.8            0.371               0   0.552                       0   118  14215.8 26  0   36.6            0.375               0   0.578                       0   119  15416.0 26  0   37.5            0.380               0   0.603                       0   108  15714.5 26  18.6        12.9            0.3445               0.575                   0.072                       8.5 67   13915.0 26  16.1        18.0            0.356               0.445                   0.177                       20.9                           62   16115.2 26  15.1        19.9            0.361               0.394                   0.2175                       25.7                           65   17415.4 26  14.2        21.8            0.366               0.342                   0.259                       30.6                           73   18015.6 26  13.4        23.6            0.371               0.291                   0.300                       36.1                           84   19715.8 26  12.5        25.5            0.375               0.239                   0.343                       41.1                           68   19116.0 26  11.6        27.1            0.380               0.188                   0.383                       46.0                           72   20315.6 20  0   41.3            0.285               0   0.711                       0   33   13815.6 22  0   39.5            0.3135               0   0.658                       0   68   14315.6 24  0   37.6            0.342               0   0.605                       0   102  14415.6 26  0   35.8            0.371               0   0.552                       0   122  14215.6 28  0   33.9            0.399               0   0.500                       0   122  14015.6 30  0   32.1            0.428               0   0.446                       0   120  14015.6 32  0   30.2            0.456               0   0.394                       0   115  12715.6 34  0   28.3            0.485               0   0.340                       0   112  10515.6 20  13.7        29.5            0.285               0.190                   0.467                       58.0                           17   2115.6 22  13.4        27.5            0.3135               0.224                   0.410                       49.3                           17   2515.6 24  13.4        25.6            0.342               0.258                   0.356                       42.7                           16   3515.6 26  13.4        23.6            0.371               0.291                   0.300                       36.1                           48   18415.6 28  13.3        21.7            0.399               0.3245                   0.246                       29.0                           74   19415.6 30  13.3        19.7            0.428               0.358                   0.190                       22.5                           100  19615.6 32  13.3        17.7            0.456               0.392                   0.135                       16.0                           106  19415.6 34  13.2        15.8            0.485               0.425                   0.080                       9.4 116  193__________________________________________________________________________ 
    
     As can be seen from the date in Table 2, the solubilization of the HEC is different in CaBr 2  ZnBr 2  solutions as opposed to CaCl 2  /CaBr 2  /ZnBr 2  solutions. As can also be seen, the calcium chloride has a retarding effect on the solubilization of the HEC, the effect being dependent upon the ZnBr 2  concentration. The data further show that CaBr 2  /ZnBr 2  solutions containing 20% ZnBr 2  and having a density in the range of from about 14.2 to about 15.6 ppg are compatible with HEC. Lastly, it can be seen that activated HEC will hydrate or solubilize at room temperature in CaBr 2  /ZnBr 2  solutions containing 20% zinc bromide provided the density is no greater than about 15.2 ppg. 
     EXAMPLE 3 
     Various brine solutions were admixed with an activated HEC containing 20% NATROSOL 250 HHR, 25% glycerol, 54.6% isopropanol and 0.4% fumed silica by mixing for 15 minutes on a Multimixer and allowing the solutions to age overnight at room temperature. The data, obtained on duplicate one gallon composite samples, are given in Table 3. 
     
                                           TABLE 3__________________________________________________________________________            1.5 ppb. Natrosol 250 HHR                      After RollingComposition of Solution            Initial   16 Hours @ 150° F.                                API (1)%   %   %   Density            API RHEOLOGY                      API RHEOLOGY                                FluidZnBr.sub.2    CaCl.sub.2   CaBr.sub.2       ppg. 600 300                   3  600 300                             3  Loss__________________________________________________________________________57  0   20  19.2 278 196                   31 262 188                             24 17.557  0   20  19.2 270 190                   31 251 179                             240   37.6   0   11.6 160 118                   17 147 106                             10 38.50   37.6   0   11.6 158 116                   16 143 103                             100   0   53  14.2 155 115                   19 152 113                             16 17.50   0   53  14.2 154 115                   18 158 117                             16__________________________________________________________________________ Sample After Rolling with 3 ppb. BARACARB Added. 
    
     EXAMPLE 4 
     Brine solutions containing 1.5 ppb of HEC were formulated by mixing various ratios of the solutions shown in Table 3. API rheology was then obtained on the solutions. The solutions were then mixed with 3 ppg of BARACARB (tradename of a CaCO 3  bridging agent marketed by NL Baroid, Houston, Tex.), and the API rheology and API fluid loss obtained on the solutions after rolling for 16 hours at 150° F. and cooling to room temperature. The data are given in Tables 4 and 5. 
     
                                           TABLE 4__________________________________________________________________________                     1.5 ppb. Natrosol 250 HHRComposition of Solution   API RHEOLOGY      (1)            19.2               11.6                  14.2       After Rolling                                       API%   %   %   Density            ppg.               ppg.                  ppg.                     Initial 16 Hours @ 150° F.                                       FluidZnBr.sub.2    CaCl.sub.2   CaBr.sub.2       ppg. bbl.               bbl.                  bbl.                     600                        300                           3 600                                300 3  Loss__________________________________________________________________________18  0   42.5       15.5 0.255               0  0.745                     35 19 1 37 20  1  7.2    2   39.8       15.3 0.251               0.070                  0.679                     27 14 1 32 17  1  2.6    4   36.9       15.1 0.248               0.139                  0.613                     30 15 1 29 15  1  8.2    6   34.1       14.9 0.245               0.205                  0.550                     27 14 1 27 14  1  9.0    8   31.3       14.7 0.242               0.270                  0.488                     25 13 1 23 12  0  5.4    10  28.5       14.5 0.239               0.334                  0.427                     23 12 1 30 16  1  5.020  0   41.4       15.6 0.286               0  0.714                     139                        100                           11                             139                                101 12 4    2   38.6       15.4 0.282               0.071                  0.647                     137                        100                           9 131                                93  7  2    4   35.8       15.2 0.278               0.140                  0.582                     134                        97 8 121                                84  4  3    6   32.9       15.0 0.275               0.207                  0.518                     127                        89 7 96 62  2  3    8   30.1       14.8 0.271               0.273                  0.456                     105                        70 3 53 30  1  0.5    10  27.3       14.7 0.269               0.337                  0.394                     77 47 2 45 25  1  1.5    12  24.5       14.5 0.264               0.399                  0.337                     24 13 1 26 13  0  3.5    14  21.3       14.3 0.261               0.460                  0.279                     24 13 1 26 14  1  4.422  0   40.3       15.8 0.317               0  0.683                     158                        116                           19                             150                                111 18 8    2   37.5       15.6 0.313               0.071                  0.616                     147                        109                           13                             148                                109 15 5    4   34.7       15.4 0.309               0.140                  0.551                     146                        108                           13                             142                                105 14 8    6   31.8       15.2 0.305               0.210                  0.485                     138                        100                           10                             131                                95  10 1.8    8   28.9       15.0 0.302               0.276                  0.422                     145                        105                           13                             137                                99  13 1.8    10  26.1       14.8 0.298               0.340                  0.362                     137                        99 12                             133                                97  11 1.8    12  23.3       14.6 0.294               0.403                  0.303                     90 59 3 54 30  1  1.2    14  20.6       14.4 0.290               0.463                  0.247                     34 18 1 36 19  1  2.224  0   39.1       15.9 0.349               0  0.651                     169                        124                           20                             166                                123 18 21    2   36.3       15.7 0.345               0.072                  0.583                     156                        116                           17                             158                                117 17 10    4   33.4       15.5 0.341               0.143                  0.516                     149                        110                           15                             152                                112 14 9    6   30.6       15.3 0.336               0.212                  0.452                     150                        111                           15                             154                                114 15 15    8   27.8       15.1 0.333               0.278                  0.389                     146                        107                           14                             150                                111 14 15    10  25.0       15.0 0.328               0.343                  0.329                     147                        107                           14                             148                                109 14 12    12  22.2       14.8 0.324               0.406                  0.270                     144                        105                           14                             146                                107 13 8    14  19.4       14.6 0.320               0.468                  0.212                     140                        102                           13                             142                                104 13 8    16  16.6       14.4 0.316               0.528                  0.156                     137                        98 12                             141                                102 12 726  0   38.0       16.1 0.381               0  0.619                     176                        129                           21                             167                                121 17 27    2   35.2       15.9 0.377               0.073                  0.550                     162                        120                           18                             162                                120 17 22    4   32.3       15.7 0.373               0.143                  0.484                     159                        118                           17                             159                                117 16 14    6   29.5       15.5 0.368               0.214                  0.418                     156                        115                           17                             158                                117 17 8    8   26.7       15.3 0.363               0.281                  0.356                     152                        112                           16                             155                                114 16 6    10  23.7       15.1 0.359               0.348                  0.293                     147                        108                           15                             153                                113 16 5    12  21.1       14.9 0.354               0.409                  0.237                     146                        107                           14                             152                                112 14 10    14  18.3       14.7 0.350               0.471                  0.179                     145                        106                           14                             147                                108 14 11    16  15.4       14.5 0.346               0.533                  0.121                     152                        111                           16                             142                                104 13 1328  14  17.1       14.9 0.380               0.477                  0.143                     168                        123                           19                             149                                110 16 12    16  14.1       14.7 0.376               0.541                  0.083                     170                        124                           19                             153                                112 14 13    18  11.1       14.5 0.372               0.605                  0.023                     163                        120                           17                             151                                110 15 1730  14  15.9       15.0 0.411               0.481                  0.108                     173                        127                           20                             162                                119 17 18__________________________________________________________________________ (1) Sample After Rolling with 3 ppb. BARACARB Added. 
    
     
                                           TABLE 5__________________________________________________________________________                     1.5 ppb. Natrosol 250 HHRComposition of Solution   API RHEOLOGY      (1)            19.2               11.6                  14.2       After Rolling                                       API%   %   %   Density            ppg.               ppg.                  ppg.                     Initial 16 Hours @ 150° F.                                       FluidZnBr.sub.2    CaCl.sub.2   CaBr.sub.2       ppg. bbl.               bbl.                  bbl.                     600                        300                           3 600                                300 3  Loss__________________________________________________________________________18  0   42.5       15.5 0.255               0  0.745                     35 19 1 37 20  1  7.220      41.4       15.6 0.286               0  0.714                     139                        100                           11                             139                                101 12 422      40.3       15.8 0.317               0  0.683                     158                        116                           19                             150                                111 18 824      39.1       15.9 0.349               0  0.651                     169                        124                           20                             166                                123 18 2126      38.0       16.1 0.381               0  0.619                     176                        129                           21                             167                                121 17 2718  2   39.8       15.3 0.251               0.070                  0.679                     27 14 1 32 17  1  2.620      38.6       15.4 0.282               0.071                  0.647                     137                        100                           9 131                                93  7  222      37.5       15.6 0.313               0.071                  0.616                     147                        109                           13                             148                                109 15 524      36.3       15.7 0.345               0.072                  0.583                     156                        116                           17                             158                                117 17 1026      35.2       15.9 0.377               0.073                  0.550                     162                        120                           18                             162                                120 17 2218  4   36.9       15.1 0.248               0.139                  0.613                     30 15 1 29 15  1  8.220      35.8       15.2 0.278               0.140                  0.582                     134                        97 8 121                                84  4  322      34.7       15.4 0.309               0.140                  0.551                     146                        108                           13                             142                                105 14 824      33.4       15.5 0.341               0.143                  0.516                     149                        110                           15                             152                                112 14 926      32.3       15.7 0.373               0.143                  0.484                     159                        118                           17                             159                                117 16 1418  6   34.1       14.9 0.245               0.205                  0.550                     27 14 1 27 14  1  920      32.9       15.0 0.275               0.207                  0.518                     127                        89 7 96 62  2  322      31.8       15.2 0.305               0.210                  0.485                     138                        100                           10                             131                                95  10 1.824      30.6       15.3 0.336               0.212                  0.452                     150                        111                           15                             154                                114 5  1526      29.5       15.5 0.368               0.214                  0.418                     156                        115                           17                             158                                117 17 818  8   31.3       14.7 0.242               0.270                  0.488                     25 13 1 23 12  0  5.420      30.1       14.8 0.271               0.273                  0.456                     105                        70 3 53 30  1  0.522      28.9       15.0 0.302               0.276                  0.422                     145                        105                           13                             137                                99  13 1.824      27.8       15.1 0.333               0.278                  0.389                     146                        107                           14                             150                                111 14 1526      26.7       15.3 0.363               0.281                  0.356                     152                        112                           16                             155                                114 16 618  10  28.5       14.5 0.239               0.334                  0.427                     23 12 1 30 16  1  520      27.3       14.7 0.269               0.337                  0.394                     77 47 2 45 25  1  1.522      26.1       14.8 0.298               0.340                  0.362                     137                        99 12                             133                                97  11 1.824      25.0       15.0 0.328               0.343                  0.329                     147                        107                           14                             148                                109 14 1226      23.7       15.1 0.359               0.348                  0.293                     147                        108                           15                             153                                113 16 520  12  24.5       14.5 0.264               0.399                  0.337                     24 13 1 26 13  0  3.522      23.3       14.6 0.294               0.403                  0.303                     90 59 3 54 30  1  1.224      22.2       14.8 0.324               0.406                  0.270                     144                        105                           14                             146                                107 13 826      21.1       14.9 0.354               0.409                  0.237                     146                        107                           14                             152                                112 14 1020  14  21.7       14.3 0.261               0.460                  0.279                     24 13 1 26 14  1  4.422      20.6       14.5 0.290               0.463                  0.247                     34 18 1 36 19  1  2.224      19.4       14.6 0.320               0.468                  0.212                     140                        102                           13                             142                                104 13 826      18.3       14.7 0.350               0.471                  0.179                     145                        106                           14                             147                                108 14 128      17.1       14.9 0.380               0.477                  0.143                     168                        123                           19                             149                                110 16 1230      15.9       15.0 0.411               0.481                  0.108                     173                        127                           20                             162                                119 17 1824  16  16.6       14.4 0.316               0.528                  0.156                     137                        98 12                             141                                102 12 726      15.4       14.5 0.346               0.533                  0.121                     152                        111                           16                             142                                104 13 1328      14.1       14.7 0.376               0.541                  0.083                     170                        124                           19                             153                                112 14 1328  18  11.1       14.5 0.372               0.605                  0.023                     163                        120                           17                             151                                110 15 17__________________________________________________________________________ (1) Sample After Rolling with 3 ppb. BARACARB Added. 
    
     As can be seen from the data in Tables 4 and 5, to be compatible with HEC, the brine solutions must contain at least about 20% ZnBr 2  and no more than about (2×-33)% calcium chloride where x is the concentration of ZnBr 2 . As further seen, fluid loss increases with increasing ZnBr 2  concentration and decrease with increasing CaCl 2  concentration. 
     EXAMPLE 5 
     Various brine solutions were prepared by mixing together various aqueous salt solutions and, in some cases, solid. Thereafter, the activated HEC used in Example 4 was added to the brine solution to produce a concentration of 1.5 ppb HEC and the solutions mixed for 5 minutes on a Multimixer. The solutions were then rolled 55 minutes at room temperature and the API rheology obtained. After rolling 16 hours at 150° F., cooling to room temperature and mixing 5 minutes on a Multimixer, API rheology and API fluid loss were obtained (the latter after adding 3 ppb BARACARB). The data obtained, together with comparison data from Table 2, are given in Tables 6-8. 
     
                                           TABLE 6__________________________________________________________________________                            1.5 ppb. Natrosol 250 HHR                            API RHEOLOGY        APICOMPOSITION OF SOLUTION          ***                 Fluid                        95% After One                                     After Rolling                                                LossDensity%   %   %   19.2                11.6                    14.2                        CaCl.sub.2                            Hour @ 74° F.                                     Overnight @ 150°                                                **ppg. ZnBr.sub.2    CaCl.sub.2        CaBr.sub.2            bbl.                bbl.                    bbl.                        lb. 600                               300                                  3  600                                        300 3   ***__________________________________________________________________________14.5 24  18.6        14.8            0.318                0.544                    0.123                        14.5                            51 28 1  102                                        59  2   014.5 26  18.6        12.8            0.3445                0.575                    0.072                        8.5 91 57 3  143                                        100 14  1.814.5 24  14.9        18.1            0.318                0.496                    0.186                        0   75 47 2  134                                        90  12  2.014.5 26  16.6        14.5            0.3445                0.552                    0.1035                        0   (83)                               (53)                                  (3)                                     (137)                                        (96)                                            (14)                                                (3.2)14.5 28  18.6        10.9            0.371                0.6056                    0.021                        2.5 93 59 3  154                                        107 15  4.214.5 28  18.0        11.5            0.371                0.5975                    0.0315                        0   91 58 3  145                                        100 14  3.414.5 28.8    18.6        10.1            0.3815                0.6185                    0   0   99 65 4  151                                        106 15  4.815.0 24  16.1        19.9            0.329                0.414                    0.228                        27.0                            41 21 0  73 38  1   0.115.0 26  16.1        18.0            0.356                0.445                    0.177                        20.9                            (62)                               (35)                                  (1)                                     (159)                                        (125)                                            (20)                                                (0.7)15.0 28  16.1        16.0            0.384                0.479                    0.122                        14.4                            73 43 1  152                                        109 16  2.615.0 24  9.5 25.8            0.329                0.325                    0.346                        0   82 51 3  148                                        104 17  1.215.0 26  10.9        22.5            0.356                0.3765                    0.2675                        0   (102)                               (71)                                  (4)                                     (156)                                        (111)                                            (19)                                                (5.0)15.0 30  16.1        14.0            0.411                0.510                    0.070                        8.3 89 57 3  179                                        127 21  3.815.0 28  12.5        12.5            0.384                0.431                    0.185                        0   98 64 4  132                                        95  12  6.015.0 32  16.1        12.1            0.4385                0.542                    0.017                        2.0 140                               91 9  191                                        138 23  5.015.0 32.6    16.1        11.5            0.4474                0.5526                    0   0   128                               87 9  175                                        124 20  9515.5 24  13.9        24.6            0.340                0.285                    0.334                        40.1                            45 23 1  73 38  2   015.5 26  13.9        22.8            0.368                0.316                    0.281                        33.8                            (68)                               (40)                                  (2)                                     (190)                                        (143)                                            (19)                                                (4.0)15.5 28  13.7        20.7            0.3965                0.350                    0.225                        26.6                            95 58 3  160                                        148 23  6.015.5 24  4.4 32.9            0.340                0.155                    0.505                        0   92 59 3  140                                        118 22  1.415.5 30  13.7        18.8            0.425                0.383                    0.171                        20.2                            (103)                               (66)                                  (3)                                     (184)                                        (146)                                            (26)                                                (24)15.5 26  5.8 29.8            0.368                0.2065                    0.4255                        0   (106)                               (71)                                  (4)                                     (160)                                        (118)                                            (21)                                                (7.5)15.5 28  7.4 26.4            0.3965                0.262                    0.3415                        0   105                               70 5  149                                        109 17  5.615.5 32  13.7        16.9            0.453                0.416                    0.117                        13.8                            (124)                               (82)                                  (6)                                     (193)                                        (140)                                            (26)                                                (23)15.5 34  13.7        14.9            0.4815                0.450                    0.0605                        7.2 127                               82 7  185                                        135 21  1115.5 36.2    13.7        12.7            0.513                0.487                    0   0   162                               111                                  15 185                                        135 22  1016.0 24.6    11.7        28.5            0.360                0.165                    0.4225                        50.6                            91 52 1  132                                        73  2   016.0 26  11.6        27.2            0.380                0.188                    0.384                        46.0                            (65)                               (36)                                  (1)                                     (197)                                        (149)                                            (17)                                                (2.0)16.0 28  11.6        25.3            0.409                0.221                    0.329                        39.4                            80 46 2  144                                        130 14  4.016.0 30  11.6        23.3            0.4385                0.257                    0.271                        32.6                            90 54 2  180                                        138 19  11.416.0 24.6    0   38.7            0.360                0   0.640                        0   135                               91 11 166                                        120 24  1316.0 32  11.5        21.3            0.468                0.292                    0.2135                        25.2                            90 55 3  220                                        156 2516.0 26  1.0 36.5            0.380                0.038                    0.582                        0   113                               76 6  167                                        123 22  5716.0 28  2.5 33.2            0.409                0.093                    0.498                        0   129                               88 8  175                                        127 23  3616.0 34  11.5        21.3            0.497                0.325                    0.158                        18.7                            94 59 3  202                                        146 25  2116.0 39.6    11.5        13.9            0.579                0.421                    0   0   (168)                               (116)                                  (16)                                     (184)                                        (135)                                            (23)                                                (35)__________________________________________________________________________ **Sample after rolling overnight at 150° F. with 3 ppb. BARACARB added. ***Data in parentheses are the average of two separate sample evaluations 
    
     
                                           TABLE 7__________________________________________________________________________                            1.5 ppb. Natrosol 250 HHR                            API RHEOLOGY        APICOMPOSITION OF SOLUTION          ***                 Fluid                        95% After One                                     After Rolling                                                LossDensity%   %   %   19.2                11.6                    14.2                        CaCl.sub.2                            Hour @ 74° F.                                     Overnight @ 150°                                                **ppg. ZnBr.sub.2    CaCl.sub.2        CaBr.sub.2            bbl.                bbl.                    bbl.                        lb. 600                               300                                  3  600                                        300 3   ***__________________________________________________________________________16.0 24.6    0   38.7            0.360                0   0.640                        0   135                               91 11 166                                        120 24  1315.5 24  4.4 32.9            0.340                0.155                    0.505                        0   92 59 3  140                                        118 22  1.415.0 24  9.5 25.8            0.329                0.325                    0.346                        0   82 51 3  148                                        104 17  1.214.5 24  14.9        18.1            0.318                0.496                    0.186                        0   75 47 2  134                                        90  12  2.016.0 24.6    11.7        28.5            0.360                0.165                    0.4225                        50.6                            91 52 1  132                                        73  2   015.5 24  13.9        24.6            0.340                0.285                    0.334                        40.1                            45 23 1  73 38  2   015.0 24  16.1        19.9            0.329                0.414                    0.228                        27.0                            41 21 0  73 38  1   0.114.5 24  18.6        14.8            0.318                0.544                    0.123                        14.5                            51 28 1  102                                        59  2   016.0 26  1.0 36.5            0.380                0.038                    0.582                        0   113                               76 6  167                                        123 22  5715.5 26  5.8 29.8            0.368                0.2065                    0.4255                        0   (106)                               (71)                                  (4)                                     (160)                                        (118)                                            (21)                                                (7.5)15.0 26  10.9        22.5            0.356                0.3765                    0.2675                        0   (102)                               (71)                                  (4)                                     (156)                                        (111)                                            (19)                                                (5.0)14.5 26  16.6        14.5            0.3445                0.552                    0.1035                        0   (83)                               (53)                                  (3)                                     (137)                                        (96)                                            (14)                                                (3.2)16.0 26  11.6        27.2            0.380                0.188                    0.384                        46.0                            (65)                               (36)                                  (1)                                     (197)                                        (149)                                            (17)                                                (2.0)15.5 26  13.9        22.8            0.368                0.316                    0.281                        35.8                            (68)                               (40)                                  (2)                                     (190)                                        (143)                                            (19)                                                (4.0)15.0 26  16.1        18.0            0.356                0.445                    0.177                        20.9                            (62)                               (35)                                  (1)                                     (159)                                        (125)                                            (20)                                                (0.7)14.5 26  18.6        12.8            0.3445                0.575                    0.072                        8.5 91 57 3  143                                        100 14  1.816.0 28  2.5 33.2            0.409                0.093                    0.498                        0   129                               88 8  175                                        127 23  3615.5 28  7.4 26.4            0.3965                0.262                    0.3415                        0   105                               70 5  149                                        109 17  5.616.0 28  11.6        25.3            0.409                0.221                    0.329                        39.4                            80 46 2  144                                        130 14  4.015.0 28  12.5        19.1            0.384                0.431                    0.185                        0   98 64 4  132                                        95  12  6.015.5 28  13.7        20.7            0.3965                0.350                    0.225                        26.6                            95 58 3  160                                        148 23  6.015.0 28  16.1        16.0            0.384                0.479                    0.122                        14.4                            73 43 1  152                                        109 16  2.614.5 28  18.0        11.5            0.371                0.5975                    0.0315                        0   91 58 3  145                                        100 14  3.414.5 28  18.6        10.9            0.371                0.6056                    0.021                        2.5 93 59 3  154                                        107 15  4.214.5 28.8    18.6        10.1            0.3815                0.6185                    0   0   99 65 4  151                                        106 15  4.816.0 30  11.6        23.3            0.4385                0.257                    0.271                        32.6                            90 54 2  180                                        138 19  1115.5 30  13.7        18.8            0.425                0.383                    0.171                        20.2                            (103)                               (66)                                  (3)                                     (184)                                        (146)                                            (26)                                                (24)15.0 30  16.1        14.0            0.411                0.510                    0.070                        8.3 89 57 3  179                                        127 21  3.816.0 32  11.5        21.3            0.468                0.292                    0.2135                        25.2                            90 55 3  220                                        156 25  2215.5 32  13.7        16.9            0.453                0.416                    0.117                        13.8                            (124)                               (82)                                  (6)                                     (193)                                        (140)                                            (26)                                                (23)15.0 32  16.1        12.1            0.4385                0.542                    0.017                        2.0 140                               91 9  191                                        138 23  5.015.0 32.6    16.1        11.5            0.4474                0.5526                    0   0   128                               87 9  175                                        124 20  9516.0 34  11.5        19.4            0.497                0.325                    0.158                        18.7                            94 59 3  202                                        146 25  2115.5 34  13.7        14.9            0.4815                0.450                    0.605                        7.2 127                               82 7  185                                        135 21  1115.5 36.2    13.7        12.7            0.513                0.487                    0   0   162                               111                                  15 185                                        135 22  1016.0 39.6    11.5        13.9            0.579                0.421                    0   0   (168)                               (116)                                  (16)                                     (184)                                        (135)                                            (23)                                                (35)__________________________________________________________________________ **Sample after rolling overnight at 150° F. with 3 ppb. BARACARB added. ***Data in parentheses are the average of two separate sample evaluations 
    
     
                                           TABLE 8__________________________________________________________________________                            1.5 ppb. Natrosol 250 HHR                            API RHEOLOGY        APICOMPOSITION OF SOLUTION          ***                 Fluid                        95% After One                                     After Rolling                                                LossDensity%   %   %   19.2                11.6                    14.2                        CaCl.sub.2                            Hour @ 74° F.                                     Overnight @ 150°                                                **ppg. ZnBr.sub.2    CaCl.sub.2        CaBr.sub.2            bbl.                bbl.                    bbl.                        lb. 600                               300                                  3  600                                        300 3   ***__________________________________________________________________________16.0 24.6    11.7        28.5            0.360                0.165                    0.4225                        50.6                            91 52 1  132                                        73  2   016.0 26  11.6        27.2            0.380                0.188                    0.384                        46.0                            (65)                               (36)                                  (1)                                     (197)                                        (149)                                            (17)                                                (2.0)16.0 28  11.6        25.3            0.409                0.221                    0.329                        39.4                            80 46 2  144                                        130 14  4.016.0 30  11.6        23.3            0.4385                0.257                    0.271                        32.6                            90 54 2  180                                        138 19  1116.0 32  11.5        21.3            0.468                0.292                    0.2135                        25.2                            90 55 3  220                                        156 25  2216.0 34  11.5        19.4            0.497                0.325                    0.158                        18.7                            94 59 3  202                                        146 25  2116.0 39.6    11.5        14.9            0.579                0.421                    0   0   (168)                               (116)                                  (16)                                     (184)                                        (135)                                            (23)                                                (35)15.5 24  13.9        24.6            0.340                0.285                    0.334                        40.1                            45 23 1  73 38  2   015.5 26  13.9        22.8            0.368                0.316                    0.281                        33.8                            (68)                               (40)                                  (2)                                     (190)                                        (143)                                            (19)                                                (4.0)15.5 28  13.7        20.7            0.3965                0.350                    0.225                        26.6                            95 58 3  160                                        148 23  6.015.5 30  13.7        18.8            0.425                0.383                    0.171                        20.2                            (103)                               (66)                                  (3)                                     (184)                                        (146)                                            (26)                                                (24)15.5 32  13.7        16.9            0.453                0.416                    0.117                        13.8                            (124)                               (82)                                  (6)                                     (193)                                        (140)                                            (26)                                                (23)15.5 34  13.7        14.9            0.4815                0.450                    0.605                        7.2 127                               82 7  185                                        135 21  1115.5 36.2    13.7        12.7            0.513                0.487                    0   0   162                               111                                  15 185                                        135 22  1015.0 24  16.1        19.9            0.329                0.414                    0.228                        27.8                            41 21 0  73 38  1   0.115.0 26  16.1        18.0            0.356                0.445                    0.177                        20.9                            (62)                               (35)                                  (1)                                     (159)                                        (125)                                            (20)                                                (0.7)15.0 28  16.1        16.0            0.384                0.479                    0.122                        14.4                            73 43 1  15.2                                        109 16  2.615.0 30  16.1        14.0            0.411                0.510                    0.070                        8.3 89 57 3  179                                        127 21  3.815.0 32  16.1        12.1            0.4385                0.542                    0.017                        2.0 140                               91 9  191                                        138 23  5.015.0 32.6    16.1        11.5            0.4474                0.5526                    0   0   128                               87 9  175                                        124 20  9514.5 24  18.6        14.8            0.318                0.544                    0.123                        14.5                            51 28 1  102                                        59  2   014.5 26  18.6        12.8            0.3445                0.575                    0.072                        8.5 91 57 3  143                                        100 14  1.814.5 28  18.6        10.9            0.371                0.6056                    0.021                        2.5 93 59 3  154                                        107 15  4.214.5 28.8    18.6        10.1            0.3815                0.6185                    0   0   99 65 4  151                                        106 15  4.8__________________________________________________________________________ **Sample after rolling overnight at 150° F. with 3 ppb. BARACARB added. ***Data in parentheses are the average of two separate sample evaluations 
    
     As can be seen from the data in Tables 6-8 even solutions in which the HEC is not solubilized or hydrated give good fluid loss control with the addition of the calcium carbonate bridging agent. Additionally, it can be seen that HEC hydrates differently in solutions containing solid calcium chloride as compared with solutions containing calcium chloride obtained via an 11.6 ppg solution. Specifically, it can be seen that solutions containing solid calcium chloride exhibit higher viscosities and lower fluid loss after hot rolling than solutions containing calcium chloride obtained from 11.6 ppg solution. Also, solutions containing solid calcium chloride require a larger concentration of ZnBr 2  for efficient hydration of the HEC at room temperature. Lastly, it can be seen that to effectively hydrate or solubilize activated HEC without heat, the brine solution should be formulated without the addition of solid calcium chloride. 
     EXAMPLE 6 
     Various brine solutions were prepared and evaluated for rheological properties as per the procedure of Example 5. The API fluid loss was obtained on the solutions after rolling 16 hours at 150° F. with and without the addition of 3 ppb BARACARB. The data are given in Table 9. 
     
                                           TABLE 9__________________________________________________________________________                            1.5 ppb. NATROSOL 250 HHRComposition of Solution          API Rheology   *   **            19.2                11.6                    14.2                        95%       After Rolling                                           API APIDensity%   %   %   ppg ppg ppg CaCl.sub.2                            Initial                                  16 Hr. @ 150° F.                                           Fluid                                               Fluidppg. ZnBr.sub.2    CaCl.sub.2        CaBr.sub.2            bbl.                bbl.                    bbl.                        lb. 600                               300                                  600 300  Loss                                               Loss__________________________________________________________________________16.0 22  11.7        31.0            0.3215                0.120                    0.496                        59.3                            40 20 54  27   0.2 0.416.0 24  11.6        29.1            0.351                0.154                    0.440                        52.6                            46 25 116 68   0   016.0 26  11.6        27.2            0.380                0.188                    0.384                        46.0                            50 26 87  53   12  3.816.0 28  11.6        25.2            0.409                0.222                    0.328                        39.3                            60 33 121 79   50  1116.5 26  9.5 31.4            0.392                0.059                    0.488                        58.2                            63 33 193 133  0   1.016.5 28  9.5 29.4            0.422                0.094                    0.430                        51.4                            87 50 179 120  6.2 6.216.5 30  9.5 27.5            0.452                0.130                    0.3715                        44.4                            101                               61 211 148  82  8.416.5 32  9.5 25.5            0.4825                0.1655                    0.313                        37.5                            112                               70 223 160  82  14.216.5 34  9.5 23.6            0.5125                0.2005                    0.255                        30.6                            116                               74 220 160  97  16.517.0 30.6    7.6 30.8            0.475                0.015                    0.453                        54.1                            84 48 162 106  10  3.417.0 32  7.6 29.5            0.497                0.040                    0.412                        49.2                            91 53 159 105  26  6.617.0 34  7.5 27.5            0.528                0.0755                    0.3525                        42.1                            106                               64 213 148  146 11.417.0 36  7.5 25.6            0.559                0.101                    0.292                        35.0                            124                               78 239 171  116 18.217.0 38  7.5 23.6            0.590                0.149                    0.232                        27.8                            126                               80 212 152  NC  17.817.5 37.5    5.7 28.1            0.593                0.012                    0.351                        41.9                            95 55 172 112  95  7.417.5 38  5.6 27.4            0.6075                0.026                    0.326                        38.9                            101                               60 248 175  112 14.917.5 40  5.6 25.4            0.6395                0.063                    0.264                        31.6                            118                               73 240 172  95  17.917.5 42  5.6 23.4            0.6715                0.101                    0.202                        24.2                            140                               91 224 162  109 20.418.0 44  3.9 25.0            0.7235                0.019                    0.229                        27.3                            158                               101                                  234 169  63  16.618.0 46  3.9 23.0            0.7565                0.058                    0.165                        19.7                            216                               148                                  226 162  65  19.1__________________________________________________________________________ *Sample after rolling @ 150° F. **Sample after rolling @ 150° F. with 3 ppb BARACARB added. 
    
     As can be seen from the data in Table 9, brine solutions having a density of from about 16.0 to 17.0 ppg containing the minimum amount of zinc bromide exhibit good fluid loss control even in the absence of a bridging agent. 
     EXAMPLE 7 
     Various thickened brine solutions were formulated by mixing together various aqueous salt solutions and the activated HEC used in Example 2. Following mixing for 5 minutes on a Multimixer, the solutions were rolled 55 minutes at 74° F. and the API rheology obtained. Thereafter, the API rheology and fluid loss were obtained after rolling the solutions at 74° F. for 16 hours and after further rolling of the solutions an additional 16 hours at 150° F. The data are given in Table 10. 
     
         TABLE 10  Composition of Brine 1.5 ppb NATROSOL 250 HHR 19.2 11.6 14.2 95%  1 Hour @ 74° F. 16 Hours @ 74° F. 16 Hours @ 150° F. Density % % % ppg. ppg. ppg. CaCl.sub.2 H.sub.2 O API Rheology* API Rheology Fluid API Rheology Fluid ppg. ZnBr.sub.2 CaCl.sub.2 CaBr.sub.2 bbl. bbl. bbl. lb. bbl. AV PV YP GS AV PV YP GS Loss AV PV YP GS Loss      14.4 20.0 7.0 29.8 0.263 0.231 0.4355 0 0.0585 34 26 16 2 47 31 32  6  8 57 37 40 15 4 14.4 26.0 18.7 11.4 0.340 0.6145 0.0455 0 0 44 31 26 3 64 42 45 11 15 74 45 58 15 5 14.6 20.4 7.8 28.8 0.272 0.261 0.419 0 0.048 28 22 12 2 46 31 30  6  8 55 39 33 18 4 14.6 24.0 13.8 19.7 0.320 0.4605 0.2195 0 0 32 26 13 1 58 39 38  9  5 67 42 51 13 7 14.8 21.2 9.4 27.4 0.2865 0.320 0.3935 0 0 18 17  2 0 46 34 24  5  5 56 39 34 19 2 14.8 23.2 11.0 24.1 0.314 0.372 0.314 0 0 37 30 15 1 65 42 46 12  7 75 45 61 16 7 14.8 25.0 12.4 21.1 0.338 0.420 0.242 0 0 38 29 19 2 68 43 50 12 14 76 47 59 16 11 15.0 22.0 7.9 29.1 0.3015 0.272 0.4265 0 0 24 22  5 0 54 37 34  8  2 66 40 52 12 4 15.0 24.0 9.5 25.8 0.329 0.325 0.346 0 0 38 29 18 2 68 43 51 13 13 76 43 67 17 5 15.0 26.0 11.0 22.4 0.3565 0.3785 0.265 0 0 44 32 24 2 68 42 53 13 11 80 48 65 18 15 15.2 22.8 6.4 30.7 0.3165 0.224 0.4595 0 0 41 30 22 2 62 40 44 12 12 70 43 55 10 11 15.2 24.8 8.0 27.4 0.3445 0.2775 0.378 0 0 57 39 37 6 80 47 66 19 16 85 37 96 26 12 15.2 26.8 9.5 24.1 0.372 0.331 0.297 0 0 54 37 35 5 74 44 60 16 24 81 47 69 21 23 15.4 23.6 5.0 32.3 0.332 0.177 0.491 0 0 40 30 20 3 65 40 51 13 17 74 42 64  9 10 15.4 25.6 6.6 28.9 0.360 0.2315 0.4085 0 0 56 40 33 6 86 51 70 19 12 88 48 80 22 17 15.4 27.6 8.1 25.7 0.3885 0.2845 0.327 0 0 68 46 45 8 83 46 75 22 12 96 51 90 27 18 15.6 24.4 3.7 33.7 0.348 0.131 0.521 0 0 49 33 32 4 71 42 58 15 21 77 40 74 19 16 15.6 26.4 5.2 30.4 0.3765 0.1845 0.439 0 0 56 35 43 7 79 45 68 19 12 87 47 81 21 14 15.6 28.4 6.7 27.1 0.405 0.240 0.355 0 0 64 43 42 8 81 46 71 20 27 88 48 81 23 14 15.8 25.2 2.3 35.1 0.364 0.0845 0.5515 0 0 52 34 36 5 77 43 69 18 35 82 43 79 22 48 15.8 27.2 3.9 31.8 0.3925 0.1405 0.467 0 0 61 41 41 8 83 45 77 23 26 91 49 85 26 33 15.8 29.2 5.4 28.5 0.4215 0.1955 0.383 0 0 66 44 44 10  89 49 80 24 37 91 49 84 25 27 16.0 26.0 1.0 36.5 0.380 0.0385 0.5815 0 0 54 33 42 6 73 40 67 18 83 81 43 77 23 120 16.0 28.0 2.6 33.1 0.4095 0.0955 0.495 0 0 67 45 44 9 84 44 81 25 21 96 50 93 29 83 16.0 30.0 4.1 29.8 0.4385 0.151 0.4105 0 0 69 45 48 11  88 46 85 24 47 95 53 85 30 60 *Av = Apparent Viscosity; PV = Plastic Viscosity; YP = Yield Point; GS = 10Second Gel Strength 
    
     As can be seen from the data in Table 10, the heavy brines containing zinc bromide, calcium bromide and calcium chloride can be readily viscosified at ambient temperature provided that the minimum percent zinc bromide in the brine is the larger of 20% or 4(D-9.5)% wherein D is the density of the solution in ppg. Preferably, the zinc concentration is greater than 4(D-9)%, more preferably greater than 4(D-8.5)%. 
     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.