GB2108174A - Thickened heavy brines - Google Patents

Abstract

Thickened heavy brines having a density of 1.702 to 2.157 kg/litre are obtained by mixing hydroxyethyl cellulose (which can optionally be activated), with an aqueous solution containing calcium bromide and at least 20% by weight (e.g. 20 to 46.9%) of zinc bromide. Optionally the solution can also contain up to (2x - 33)% by weight of calcium chloride, where x is the weight percentage of zinc bromide. In the presence of less than 20% of zinc bromide, the hydroxyethyl cellulose will not increase the viscosity of the brine.

Description

SPECIFICATION Thickened heavy brines The present invention relates to thickened brine solutions and, more particularly, to so called heavy brines having a density of 1.702 kg/litre 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 weli servicing fluids, e.g. in work-over and completion operations.

Heavy brine solutions having a density greater than 1.797 kg/litre 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 1.702 to 1.797 kg/litre 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 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.

It is therefore an object of the present invention to provide thickened brine solutions containing zinc bromide and HEC and a method for preparing such thickened brines.

In one embodiment, the present invention provides a thickened brine solution having a density in the range of from about 1.702 to 2.157 kg/litre which comprises water, at least 20 weight percent of zinc bromide, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose.

In another embodiment, the present invention provides a method of preparing thickened brines which comprises mixing an aqueous solution having a density in the range of from 1.702 to 2.157 kg/l and which comprises water, at least 20 weight percent of zinc bromide and calcium bromide, with a viscosifying amount of hydroxyethyl cellulose.

The present invention is based on the discovery that if the zinc bromide concentration in a brine solution is kept at least 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 "activated" 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 1.702 kg/litre without the necessity for mixing, as by rolling, at elevated temperatures. Examples of such activated HEC polymers are to be found in British Patent Applications No. 8101828 and 8109880. 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 1.702 kg/litre at room temperature can be considered an "activated" 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 "compatible" 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), kg/litre Minimum % ZnBr2 1.702-1.873 20 -1.873-2.157 (131.14) (D-d) D (2.301-d) where d is the density (ppg) of a solution mixed with a zinc bromide solution having a density of 2.301 kg/litre. In instances where another solution containing zinc bromide is used rather than a 2.301 kg/l zinc bromide solution, the minimum percent zinc bromide which can be used in a brine having a density of from 1.873 to 2.157 kg/l is (w) (p) (D-d) D (w-d) 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 (2x-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), kg/litre Minimum % ZnBr2 1.702-1.873 20 1.873-2.037 71.518D-1 13.7 CASE 3:ZnBr2/CaBr2 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), kg/l Minimum % ZnBr2 1.702-1.821 20 1.821-1.917 47.985D- 67.4 1.917-2.157 (131.14) (D-d) D (2.301-d) where d is the density (ppg) of a solution containing only calcium bromide which is mixed with a 2.301 kg/l zinc bromide solution. If another solution-containing zinc bromide replaces the 2.301 kg/l zinc bromide solution, then the minimum percent zinc bromide in the density range from 1.917 to 2.157 kg/l is (w) (p) (D-d) D (w-d) where w is the density (ppg) of the zinc bromide solution and p is the percent zinc bromide in the solution.

CASE 4: ZnBr2/CaBr2 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 (2x33)% where x is the percent zinc bromide in the solution. The minimum percent zinc bromide in the solution is as follows: Solution Density (D), kg/l Minimum % ZnBr2 1.702-1.738 20 1.738-1.983 33.38(D-1.138) 1.738-2.037 33.38(D-1.078) 1.738-2.091 33.38(D-1.019) wherein D is the density of the brine solution in kg/l.

In formulating the thickened brines of the present invention, the HEC will be present in a viscosifying amount, generally in a concentration of from 2.853 to 14.265 gm./litre.

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: 2.301 kg/l solution aqueous solution containing 20% CaBr2 and 57% ZnBr2 1.702 kg/l solution aqueous solution containing 53% CaBr2 1.390 kg/l solution aqueous solution containing 37.6% CaC12 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 8.559 kg/l 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 65.5"C to determine the final viscosity. The data obtained are given in Table 1.

Table 1 Composition of Solution 8.559 g/1. NATROSOL 250 HHR 2.301 1.390 1.702 95% Fann 300 rpm Reading Density % % % kg/1. kg/1. kg/1. CaCl2 After Rolling kg/1. ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. Initial 16 Hr. @ 65.5 C* 1.797 11.7 0 46.2 25.44 0 133.53 0 7 14 1.809 13.0 0 45.5 28.61 0 130.36 0 7 27 1.833 15.7 0 43.9 34.97 0 124.00 0 10 37 1.857 18.4 0 42.4 41.33 0 117.64 0 48 222 1.893 22.2 0 40.2 50.87 0 108.10 0 130 OS 1.917 24.6 0 38.7 57.23 0 101.74 0 127 OS 1.977 30.5 0 35.3 73.13 0 85.84 0 154 OS 2.037 36.1 0 32.1 89.02 0 69.95 0 197 OS 2.097 41.3 0 29.1 104.92 0 54.05 0 OS OS 2.157 46.2 0 26.3 120.82 0 38.15 0 OS OS 2.217 50.9 0 23.6 136.71 0 22.26 0 OS OS 2.277 55.3 0 21.0 152.61 0 6.36 0 OS OS 1.797 0 16.3 43.2 0 4.55 137.30 46.76 291 OS 1.809 1.7 15.8 42.5 3.82 4.45 134.01 45.63 29 29 1.833 5.1 14.9 41.1 11.29 4.29 127.50 43.45 29 24 1.857 8.4 13.9 39.8 18.92 3.97 120.98 41.18 28 26 1.893 13.2 12.5 37.8 30.20 3.66 111.28 37.86 23 25 1.917 16.3 11.6 36.6 37.83 3.50 104.60 35.64 25 24 1.977 23.7 9.5 33.6 56.75 2.86 88.23 30.05 28 175 2.037 30.6 7.5 30.7 75.69 2.38 72.01 24.52 38 160 2.097 37.1 5.7 28.1 94.11 1.91 55.64 18.93 75 OS 2.157 43.1 3.9 25.5 113.50 1.27 39.27 13.39 158 OS 2.217 49.3 2.2 23.1 132.42 0.79 22.89 7.81 OS OS 2.272 54.8 0.6 20.9 151.34 0.22 6.60 2.22 OS OS * OS = Off-scale, > 300.

As can be seen from Table 1, solutions containing less than about 20% ZnBr2 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 5.706 g/l HEC. The solutions were then rolled 55 minutes at room temperature and the Fann 300 rpm readings obtained.

Following rolling for 16 hours at 65.5"C, 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 5.706 kg/1 NATROSOL 250 HHR 2.301 1.390 1.702 95% Fann 300 rpm Reading Density % % % kg/1. kg/1. kg/1 CaCl2 After Rolling kg/1. ZSnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg.Initial 16 Hr. @ 65.5 C 1.738 20 0 36.1 42.13 0 89.18 0 73 110 1.797 20 0 38.5 43.56 0 99.83 0 75 125 1.821 20 0 39.5 44.19 0 104.28 0 57 132 1.845 20 0 40.4 44.67 0 108.58 0 37 132 1.869 20 0 41.3 45.31 0 113.03 0 33 138 1.893 20 0.02 40.9 45.94 0 113.03 0.07 31 138 1.917 20 0.05 40.3 46.42 0 112.55 0.16 30 142 1.738 20 18.6 18.8 42.13 76.46 35.93 12.12 10 16 1.797 20 16.2 23.8 43.56 55.64 53.10 18.20 13 19 1.821 20 15.3 25.7 44.19 47.21 60.09 20.57 14 19 1.845 20 14.3 27.6 44.67 38.79 67.09 22.93 17 19 1.869 20 13.7 29.5 45.31 30.20 74.24 26.33 17 21 1.893 20 12.5 31.3 45.94 21.94 80.92 27.65 20 21 1.917 20 11.7 33.1 46.42 13.51 88.07 30.01 20 25 1.738 26 0 30.6 54.77 0 65.65 0 86 109 1.797 26 0 33.0 56.60 0 75.83 0 93 122 1.821 26 0 34.0 57.39 0 79.80 0 101 128 1.845 26 0 34.9 58.18 0 83.78 0 114 140 1.869 26 0 35.8 58.98 0 87.75 0 118 142 1.893 26 0 36.6 59.61 0 91.88 0 119 154 1.917 26 0 37.5 60.41 0 95.86 0 108 157 1.738 26 18.6 12.9 54.77 91.41 11.45 3.86 67 139 1.797 26 16.1 18.0 56.60 70.74 28.14 9.49 62 161 1.821 26 15.1 19.9 57.39 62.63 34.58 11.67 65 174 1.845 26 14.2 21.8 58.18 54.37 41.17 13.89 73 180 1.869 26 13.4 23.6 58.98 46.26 47.69 16.39 84 197 1.893 26 12.5 25.5 59.61 37.99 54.53 18.66 68 191 1.917 26 11.6 27.1 60.41 29.89 60.89 20.88 72 203 Table 2 (Contd.) Composition Solution 5.706 kg/1 NATROSOL 250 HHR 2.301 1.390 1.702 95% Fann 300 rpm Reading Density % % % kg/1. kg/1. kg/1. CaCl2 After Rolling kg/1. ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) Kg.Initial 16 Hr. @ 65.5 C 1.869 20 0 41.3 45.31 0 113.03 0 33 138 1.869 22 0 39.5 49.84 0 104.60 0 68 143 1.869 24 0 37.6 54.37 0 96.18 0 102 144 1.869 26 0 35.8 58.98 0 87.75 0 122 142 1.869 28 0 33.9 63.43 0 79.48 0 122 140 1.869 30 0 32.1 68.04 0 70.80 0 120 140 1.869 32 0 30.2 72.49 0 62.63 0 115 127 1.869 34 0 28.3 77.10 0 54.05 0 112 105 1.869 20 13.7 29.5 45.31 30.20 74.24 26.33 17 21 1.869 22 13.4 27.5 49.84 35.61 65.18 22.38 17 25 1.869 24 13.4 25.6 54.37 41.01 56.59 19.39 16 35 1.869 26 13.4 23.6 58.98 46.26 47.69 16.39 48 184 1.869 28 13.3 21.7 63.43 51.59 39.11 13.17 74 194 1.869 30 13.3 19.7 68.04 56.91 30.20 10.22 100 196 1.869 32 13.3 17.7 72.49 62.32 21.46 7.26 106 194 1.869 34 13.2 15.8 77.10 67.56 12.72 4.27 116 193 As can be seen from the date in Table 2, the solubilization of the HEC is different in CaBr2 ZnBr2 solutions as opposed to CaCI2/CaBr2/ZnBr2 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 ZnBr2 concentration. The data further show that Ca Br2/Zn Br2 solutions containing 20% ZnBr2 and having a density in the range of from 1.702 to 1.869 kg/l are compatible with HEC.

Lastly, it can be seen that activated HEC will hydrate or solubilize at room temperature in CaBr2/ZnBr2 solutions containing 20% zinc bromide provided the density is no greater than 1.821 kg/l.

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 3.785 litre composite samples, are given in Table 3.

Table 3 4.2795 g/1. NATROSOL 250 HHR After Rolling Composition of Solution 16 Hours @ 65.5 C API RHEOLOGY API RHEOLIGY API (1) % % % Density Fluid ZnBr2 CaCl2 CaBr2 kg/1. 600 300 3 600 300 3 Loss 57 0 20 2.30 278 196 31 262 188 24 17.5 57 0 20 2.30 270 190 31 250 179 24 0 37.6 0 1.39 160 118 17 147 106 10 38.5 0 37.6 0 1.39 158 116 16 143 103 10 0 0 53 1.70 155 115 19 152 113 16 17.5 0 0 53 1.70 154 115 18 158 117 16 (1) Sample After Rolling with 8.559 g/1. BARACARB Added.

EXAMPLE 4 Brine solutions containing 4.2795 g/l 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 8.559 g/l of BARACARB (tradename of a CaCo3 bridging agent marketed by NL Baroid, Houston, Texas), and the API rheology and API fluid loss obtained on the solutions after rolling for 16 hours at 65.5"C and cooling to room temperature. The data are given in Tables 4 and 5.

Table 4 Composition of Solution 4.2795 g/1 NATROSOL 250 HHR API RHEOLOGY 2.301 1.390 1.702 After Rolling API (1) % % % Density kg/1. kg/1. kg/1. Initial 16 Hr. @ 65.5 C Fluid ZnBr2 CaCl2 CaBr2 kg/1. (litre) (litre) (litre) 600 300 3 600 300 3 Loss 18 0 42.5 1.857 40.54 0 119.07 35 19 1 37 20 1 7.2 2 39.8 1.833 39.90 11.13 107.94 27 14 1 32 17 1 2.6 4 36.9 1.809 39.42 22.10 97.45 30 15 1 29 15 1 8.2 6 34.1 1.785 38.95 32.59 87.43 27 14 1 27 14 1 9.0 8 31.3 1.761 38.47 42.92 77.58 25 12 1 23 12 0 5.4 10 28.5 1.738 37.99 53.10 67.88 23 12 1 30 16 1 5.0 20 0 41.4 1.869 45.31 0 113.50 139 100 11 139 101 12 4 2 38.6 1.845 44.83 11.29 102.85 137 100 9 131 93 7 2 4 35.8 1.821 44.19 22.56 92.52 134 97 8 121 84 4 3 6 32.9 1.797 43.71 32.91 82.35 127 89 7 96 62 2 3 8 30.1 1.773 43.08 43.40 72.49 105 70 3 53 30 1 0.5 10 27.3 1.761 42.76 53.57 62.63 77 47 2 45 25 1 1.5 12 24.5 1.737 41.97 63.43 53.57 24 13 1 26 13 0 3.5 14 21.7 1.714 41.49 73.13 44.35 24 13 1 26 14 1 4.4 22 0 40.3 1.893 50.39 0 108.58 158 116 19 150 111 18 8 2 37.5 1.869 49.76 11.29 97.93 147 109 13 148 109 15 5 4 34.7 1.845 49.12 22.56 87.59 146 108 13 142 105 14 8 6 31.8 1.821 48.49 33.38 77.10 138 100 10 131 95 10 1.8 8 28.9 1.797 48.01 43.88 67.09 145 105 13 137 99 13 1.8 10 26.1 1.773 47.37 54.05 57.55 137 99 12 133 97 11 1.8 12 23.3 1.750 46.74 64.06 48.17 90 59 3 54 30 1 1.2 14 20.6 1.726 46.10 73.60 39.27 34 18 1 36 19 1 2.2 24 0 39.1 1.905 55.48 0 103.49 169 124 20 166 123 18 21 2 36.3 1.881 54.84 11.45 92.68 156 116 17 158 117 17 10 4 33.4 1.857 54.21 22.73 82.03 149 110 15 152 112 14 9 6 30.6 1.833 53.41 33.70 71.85 150 111 15 154 114 15 15 8 27.8 1.809 52.94 44.19 61.84 146 107 14 150 111 14 15 Table 4 (Contd.) Composition of Solution 4.2795 g/1 NATROSOL 250 HHR 2.301 1.390 1.702 After Rolling API (1) % % % Density kg/1. kg/1. kg/1. Initial 16 Hr. @ 65.5 C Fluid ZnBr2 CaCl2 CaBr2 kg/1. (litre) (litre) (litre) 600 300 3 600 300 3 Loss 24 10 25.0 1.797 52.14 54.53 52.30 147 107 14 148 109 14 12 12 22.2 1.773 51.51 64.54 42.92 144 105 14 146 107 13 8 14 19.4 1.750 50.87 74.40 33.70 140 102 13 142 104 13 8 16 16.6 1.726 50.23 83.94 24.80 137 98 12 141 102 12 7 26 0 38.0 1.929 60.57 0 89.40 176 129 21 167 121 17 27 2 35.2 1.905 59.93 11.60 87.43 162 120 18 162 120 17 22 4 32.3 1.881 59.30 22.73 76.94 159 118 17 159 117 16 14 6 29.5 1.857 58.50 34.02 66.45 156 115 17 158 117 17 8 8 26.7 1.833 57.71 44.67 56.59 152 112 16 155 114 16 6 10 23.7 1.809 57.07 55.32 46.58 147 108 15 153 113 16 5 12 21.1 1.785 56.28 65.02 37.68 146 107 14 152 112 14 10 14 18.3 1.761 55.64 74.87 28.46 145 105 14 147 103 14 11 16 15.4 1.738 55.00 84.73 19.24 152 111 16 142 104 13 13 28 14 17.1 1.785 60.41 75.83 22.73 168 123 19 149 110 16 12 16 14.1 1.761 59.77 86.00 13.19 170 124 19 153 112 14 13 18 11.1 1.738 59.14 96.18 3.66 163 120 17 151 110 15 17 30 14 15.9 1.797 65.34 76.46 17.17 173 127 20 162 119 17 18 (1) Sample After Rolling with 8.559 g/1. BARACARB Added.

Table 5 4.2795 g/1 NATROSOL 250 HHR Composition of Solution API RHEOLOGY 2.301 1.390 1.702 After Rolling API (1) % % % Density kg/1. kg/1. kg/1. Initial 16 Hr. @ 65.5 C Fluid ZnBr2 CaCl2 CaBr2 kg/1. (litre) (litre) (litre) 600 300 3 600 300 3 Loss 18 0 42.5 1.857 40.54 0 118.43 35 19 1 37 20 1 7.2 20 41.4 1.869 45.47 0 113.50 139 100 11 139 101 12 4 22 40.3 1.893 50.39 0 108.58158 116 19 150 111 18 8 24 39.1 1.905 55.48 0 103.49 169 124 20 166 123 18 21 26 38.0 1.929 60.57 0 98.40 176 129 21 167 121 17 27 18 2 39.8 1.833 39.90 11.13 107.94 27 14 1 32 17 1 2.6 20 38.6 1.845 44.83 11.29 102.85 137 100 9 131 93 7 2 22 37.5 1.869 49.76 11.29 97.93 147 109 13 148 109 15 5 24 36.3 1.881 54.84 11.45 92.68 156 116 17 158 117 17 10 26 35.2 1.905 59.93 11.60 87.43 162 120 18 162 120 17 22 18 4 36.9 1.809 39.42 22.10 97.45 30 15 1 29 15 1 8.2 20 35.8 1.821 44.19 22.26 92.52 134 97 8 121 84 4 3 22 34.7 1.845 49.12 22.26 87.59 146 108 13 142 105 14 8 24 33.4 1.857 54.21 22.73 82.03 149 110 15 152 112 14 9 26 32.3 1.881 59.30 22.73 76.94 159 118 17 159 117 16 14 18 6 34.1 1.785 38.95 32.59 87.43 27 14 1 27 14 1 9 20 32.9 1.797 43.72 32.91 82.35 127 89 7 96 62 2 3 22 31.8 1.821 48.49 33.38 77.10 138 100 10 131 95 10 1.8 24 30.6 1.833 53.41 33.70 71.85 150 111 15 154 114 5 15 26 29.5 1.857 58.50 34.02 66.45 156 115 17 158 117 17 8 18 8 31.3 1.761 38.47 43.92 77.58 25 12 1 23 12 0 5.4 20 30.1 1.773 43.08 43.40 72.49 105 70 3 53 30 1 0.5 22 28.9 1.797 48.01 43.88 67.09 145 105 13 137 99 13 1.8 24 27.8 1.809 52.94 44.19 61.84 146 107 14 150 111 14 15 26 26.7 1.833 57.71 44.67 56.59 152 112 16 155 114 16 6 Table 5 (Contd) 4.2795 g/1 NATROSOL 250 HHR Composition of Solution API RHEOLOGY 2.301 1.390 1.702 After Rolling API (1) % % % Density kg/1. kg/1. kg/1. Initial 16 Hr. @ 65.5 C Fluid ZnBr2 CaCl2 CaBr2 kg/1. (litre) (litre) (litre) 600 300 3 600 300 3 Loss 18 10 28.5 1.738 37.99 53.10 67.88 23 12 1 30 16 1 5 20 27.3 1.761 42.76 53.57 62.63 77 47 2 45 25 1 1.5 22 26.1 1.773 47.37 54.05 57.55 137 99 12 133 97 11 1.8 24 25.0 1.797 52.14 54.53 52.30 147 107 14 148 109 14 12 26 23.7 1.809 57.07 55.32 46.58 147 108 15 153 113 16 5 20 12 24.5 1.738 41.97 63.43 53.57 24 13 1 26 13 0 3.5 22 23.3 1.750 46.74 64.06 48.17 90 59 3 54 30 1 1.2 24 22.2 1.773 51.51 64.54 42.92 144 105 14 146 107 13 8 26 21.1 1.785 56.28 65.02 37.68 146 107 14 152 112 14 10 20 14 21.7 1.714 41.49 73.13 44.35 24 13 1 26 14 1 4.4 22 20.6 1.738 46.10 73.60 39.27 34 18 1 36 19 1 2.2 24 19.4 1.750 50.87 74.40 33.70 140 102 13 142 104 13 8 26 18.3 1.761 55.64 74.87 28.46 145 106 14 147 108 14 11 28 17.1 1.785 60.41 75.83 22.73 168 123 19 149 110 16 12 30 15.9 1.797 65.34 76.46 17.17 173 127 20 162 119 17 18 24 16 16.6 1.726 50.23 83.94 24.80 137 98 12 141 102 12 7 26 15.4 1.738 55.00 84.73 19.23 152 111 16 142 104 13 13 28 14.1 1.761 59.77 86.00 13.19 170 121 19 153 112 14 13 28 18 11.1 1.738 59.14 96.18 3.66 163 120 17 151 110 15 17 (1) Sample After Rolling with 8.559 g/1. 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% ZnBr2 and no more than about (2x-33)% calcium chloride where x is the concentration of ZnBr2. As further seen, fluid loss increases with increasing ZnBr2 concentration and decreases with increasing CaCI2 concentration.

EXAMPLE 5 Various brine solutions were prepared by mixing together various aqueous salt solutions and, in some cases, solid calcium chloride. Thereafter, the activated HEC used in Example 4 was added to the brine solution to produce a concentration of 4.2795 g/l 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 1 6 hours at 65S5 C, cooling to room temperature and mixing 5 minutes on a Multimixer, API rheology and API fluid loss were obtained (the latter after adding 8.559 g/l BARACARB). The data obtained, together with comparison data from Table 2, are given in Tables 6-8.

Table 6 4.2795 g/1 NATROSOL 250 HHR COMPOSTITION OF SULUTION *** API Fluid 2.301 1.390 1.702 95% After One After Rolling Loss Density % % % kg/1. kg/1. kg/1. CaCl2 Hour @ 23 C Overnight @ 65.5 C ** kg/1. ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. 600 300 3 600 300 3 *** 1.738 24 18.6 14,8 50.55 86,48 19.55 6.58 51 28 1 102 59 2 0 " 26 18.6 12.8 54.77 91.41 11.45 3.86 91 57 3 143 100 14 1.8 " 24 14.9 18.1 50.55 78.85 29.57 0 75 47 2 134 90 12 2.0 " 26 16.6 14.5 54.77 87.75 16.45 0 (83) (53) (3) (137) (96) (14) (3.2) " 28 18.6 10.9 58.98 96.27 3.34 1.14 93 59 3 154 107 15 4.2 " 28 18.0 11.5 58.98 94.98 5.01 0 91 58 3 145 100 14 3.4 " 28.8 18.6 10.1 60.65 98.32 0 0 99 65 4 151 106 15 4.8 1.797 24 16.1 19.9 52.30 65.81 36.24 12.26 41 21 0 73 38 1 0.1 " 26 16.1 18.0 56.59 70.74 28.14 9.49 (62) (35) (1) (159) (125) (20) (0.7) " 28 16.1 16.0 61.04 76.15 19.39 6.54 73 43 1 152 109 16 2.6 " 24 9.5 25.8 52.30 51.67 55.00 0 82 51 3 148 104 17 1.2 " 26 10.9 22.5 56.59 59.85 42.52 0 (102) (71) (4) (156) (111) (19) (5.0) " 30 16.1 14.0 65.34 81.07 11.13 3.77 89 57 3 179 127 21 3.8 " 28 12.5 12.5 61.04 68.52 29.41 0 98 64 4 132 95 12 6.0 " 32 16.1 12.1 69.71 86.16 2.70 0.91 140 91 9 191 138 23 5.0 " 32.6 16.1 11.5 71.12 87.85 0 0 128 87 9 175 124 20 95 Table 6 (Contd) 4.2795 g/1 NATROSOL 250 HHR API RHEOLOGY COMPOSITION OF SOLUTION *** API Fluid 2.301 1.390 1.702 95% After One After Rolling Loss Density % % % kg/1. kg/1. kg/1. CaCl2 Hour @ 23 C Overnight @ 65.5 C ** kg/1.ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. 600 300 3 600 300 3 *** 1.857 24 13.9 24.6 54.05 45.31 53.10 18.21 45 23 1 73 38 2 0 " 26 13.9 22.8 58.50 50.23 44.67 15.35 (68) (40) (2) (190) (143) (19) (4.0) " 28 13.7 20.7 63.03 55.64 35.77 12.08 95 58 3 160 148 23 6.0 " 24 4.4 32.9 54.05 24.64 80.28 0 92 59 3 140 118 22 1.4 " 30 13.7 18.8 67.56 60.89 27.18 9.17 (103) (66) (3) (184) (146) (26) (24) " 26 5.8 29.8 58.50 32.83 67.64 0 (106) (71) (4) (160) (118) (21) (7.5) " 28 7.4 26.4 63.03 41.65 54.29 0 105 70 5 149 109 17 5.6 " 32 13.7 16.9 72.01 66.13 18.60 6.27 (124) (82) (6) (193) (140) (26) (23) " 34 13.7 14.9 76.54 71.54 9.62 3.27 127 82 7 185 135 21 11 " 36.2 13.7 12.7 81.55 77.42 0 0 162 111 15 185 135 22 10 1.917 24.6 11.7 28.5 57.23 26.23 67.16 22.97 91 52 1 132 73 2 0 " 26 11.6 27.2 60.41 29.89 61.04 20.88 (65) (36) 91) (197) (149) (17) (2.0) " 28 11.6 25.3 65.02 35.13 52.30 17.89 80 46 2 144 130 14 4.0 " 30 11.6 23.3 69.71 40.86 43.08 14.80 90 54 2 180 138 19 11.4 " 24.6 0 38.7 57.23 0 101.74 0 135 91 11 166 120 24 13 " 32 11.5 21.3 74.40 46.42 33.94 11.44 90 55 3 220 156 25 " 26 1.0 36.5 60.41 6.04 92.52 0 113 76 6 167 123 22 57 " 28 2.5 33.2 65.02 14.78 79.17 0 129 88 8 175 127 23 36 " 34 11.5 21.3 79.01 51.67 25.12 8.49 94 59 3 202 146 25 21 " 39.6 11.5 13.9 92.04 66.93 0 0 (168) (116) (16) (184) (135) (23) (35) ** Sample after rolling overnight at 65.5 C with 8.559 g/1. BARACARB added.

*** Data in aprentheses are the average of two separate sample evaluations.

Table 7 4.2795 g/1 NATROSOL 250 HHR API RHEOLOGY COMPOSITION OF SOLUTION *** API Fluid 2.301 1.390 1.702 95% After One After Rolling Loss Density % % % kg/1. kg/1. kg/1. CaCl2 Hour @ 23 C Overnight @ 65.5 C ** kg/1. ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. 600 300 3 600 300 3 *** 1.917 24.6 0 38.7 57.23 0 101.74 0 135 91 11 166 120 24 13 1.857 24 4.4 32.9 54.05 24.64 80.28 0 92 59 3 140 118 22 1.4 1.797 24 9.l5 25.8 52.30 51.67 55.00 0 82 51 3 148 104 17 1.2 1.738 24 14.9 18.1 50.55 78.85 29.57 0 75 47 2 134 90 12 2.0 1.917 24.6 11.7 28.5 57.23 26.23 67.16 22.97 91 52 1 132 73 2 0 1.857 24 13.9 24.6 54.05 45.31 53.10 18.20 45 23 1 73 38 2 0 1.797 24 16.1 19.9 52.30 65.81 36.25 12.26 41 21 0 73 38 1 0.1 1.738 24 18.6 14.8 50.55 86.48 19.55 6.58 51 28 1 102 59 2 0 1.917 26 1.0 36.5 60.41 6.04 92.52 0 113 76 6 167 123 22 57 1.857 26 5.8 29.8 58.50 32.83 67.64 0 (106) (71) (4) (160) (118) (21) (7.5) 1.797 26 10.9 22.5 56.60 59.85 42.52 0 (102) (71) (4) (156) (111) (19) (5.0) 1.738 26 16.6 14.5 54.77 87.75 16.45 0 (83) (53) (3) (137) (96) (14) (3.2) 1.917 26 11.6 27.2 60.41 29.89 61.04 20.88 (65) (36) (1) (197) (149) (17) (2.0) 1.857 26 13.9 22.8 58.50 50.23 44.67 16.25 (68) (40) (2) (190) (143) (19) (4.0) 1.797 26 16.1 18.0 56.60 70.74 28.14 9.49 (62) (35) (1) (159) (125) (20) (0.7) 1.738 26 18.6 12.8 54.77 91.41 11.45 3.86 91 57 3 143 100 14 1.8 1.917 28 2.5 33.2 65.02 14.78 79.17 0 129 88 8 175 127 23 36 1.857 28 7.4 26.4 63.03 41.65 54.29 0 105 70 5 149 109 17 5.6 1.917 28 11.6 25.3 65.02 35.13 52.30 17.89 80 46 2 144 130 14 4.0 1.797 28 12.5 19.1 61.04 68.52 29.41 98 64 4 132 95 12 6.0 1.857 28 13.7 20.7 63.03 55.64 35.77 12.08 95 58 3 160 148 23 6.0 1.797 28 16.1 16.0 61.04 76.15 19.39 6.54 73 43 1 152 109 16 2.6 1.738 28 18.0 11.5 58.98 94.98 5.01 91 58 3 145 100 14 3.4 1.738 28 18.6 10.9 58.98 96.27 3.34 1.14 93 59 3 154 107 15 4.2 1.738 28.8 18.6 10.0 60.65 98.32 0 0 99 65 4 151 106 15 4.8 Table 7(Contd) 4.2795 g/1 NATROSOL 250 HHR API RHEOLOGY COMPOSITION OF SOLUTION *** API Fluid 2.301 1.390 1.702 95% After One After Rolling Loss Density % % % kg/1. kg/1. kg/1. CaCl2 Hour @ 23 C Overnight @ 65.5 C ** kg/1.ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. 600 300 3 600 300 3 *** 1.917 30 11.6 23.3 69.71 40.86 43.08 14.80 90 54 2 180 138 19 11 1.857 30 13.7 18.8 67.56 60.89 27.18 9.17 (103) (66) (3) (184) (146) (26) (24) 1.797 30 16.1 14.0 65.34 81.07 11.13 3.77 89 57 3 179 127 21 3.8 1.917 32 11.5 21.3 74.40 46.42 33.94 11.44 90 55 3 220 156 25 22 1.857 32 13.7 16.9 72.01 66.13 18.60 6.27 (124) (82) (6) (193) (140) (26) (23) 1.797 32 16.1 12.1 69.71 86.16 2.70 0.91 140 91 9 191 138 23 5.0 1.797 32.6 16.1 11.5 71.12 87.85 0 0 128 87 9 175 124 20 95 1.917 34 11.5 19.4 79.01 51.67 25.12 8.49 94 59 3 202 146 25 21 1.857 34 13.7 14.9 76.54 71.54 9.62 3.27 127 82 7 185 135 21 11 1.857 36.2 13.7 12.7 81.55 77.42 0 0 162 111 15 185 135 22 10 1.917 39.6 11.5 13.9 92.04 66.93 0 0 (168) (116) (16) (184) (135) (23) (35) ** Sample aftr rolling overnight at 65.5 C with 8.559 g/1. BARACARB added.

*** Data in parentheses are the average of two separate sample evaluation.

Table 8 4.2795 g/1 NATROSOL 250 HHR API RHEOLOGY COMPOSITION OF SOLUTION *** API Fluid 2.301 1.390 1.702 95% After One After Rolling Loss Density % % % kg/1. kg/1. kg/1. CaCl2 Hour @ 23 c Overnight @ 65.5 C ** kg/1. ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. 600 300 3 600 300 3 *** 1.917 24.6 11.7 28.5 57.23 26.23 67.16 22.97 91 52 1 132 73 2 0 " 26 11.6 27.2 60.41 29.89 61.04 20.88 (65) (36) (1) (197) (149) (17) (2.0) " 28 11.6 25.3 65.02 35.13 52.30 17.89 80 46 2 144 130 14 4.0 " 30 11.6 23.3 69.71 40.86 43.08 14.80 90 54 2 180 138 19 11 " 32 11.5 21.3 74.40 46.42 33.94 11.44 90 55 3 220 156 25 22 " 34 11.5 19.4 79.01 51.67 25.12 8.49 94 59 3 202 146 25 21 " 39.6 11.5 14.9 92.04 66.93 0 0 (168) (116) (16) (184) (135) (23) (35) 1.857 24 13.9 24.6 54.05 45.31 53.10 18.21 45 23 1 73 38 2 0 " 26 13.9 22.8 58.50 50.23 44.67 15.35 (68) (40) (3) (190) (143) (19) (4.0) " 28 13.7 20.7 63.03 55.64 35.77 12.08 95 53 3 160 148 23 6.0 " 30 13.7 18.8 67.56 60.89 27.18 9.17 (103) (66) (3) (184) (146) (26) (24) " 32 13..7 16.9 72.01 66.13 18.60 6.27 (124) (82) (6) (193) (140) (26) (23) " 34 13.7 14.9 76.54 71.54 9.62 3.27 127 82 7 185 135 21 11 " 36.2 13.7 12.7 81.55 77.42 0 0 162 111 15 185 135 22 10 1.797 24 16.1 19.9 52.30 65.81 36.25 12.62 41 21 0 73 38 1 0.1 " 26 16.1 18.0 56.59 70.74 28.14 9.49 (62) (35) (1) (159) (125) (20) (0.7) " 28 16.1 16.0 61.04 76.15 19.39 6.54 73 43 1 15.2 109 16 2.6 " 30 16.1 14.0 65.34 81.07 11.13 3.77 89 57 3 179 127 21 3.8 " 32 16.1 12.1 69.71 86.16 2.70 0.91 140 91 9 191 138 23 5.0 " 32.6 16.1 11.5 71.12 87.85 0 0 128 87 9 175 124 20 95 Table 8 (Contd) 4.2795 g/1 NATROSOL 250 HHR API RHEOLOGY COMPOSITION OF SOLUTION *** API Fluid 2.301 1.390 1.702 95% After One After Rolling Loss Density % % % kg/1. kg/1. kg/1. CaCl2 Hour @ 23 C Overnight @ 65.5 C ** kg/1. ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. 600 300 3 600 300 3 *** 1.738 24 18.6 14.8 50.55 86.48 19.55 51 28 1 102 59 2 0 " 26 18.6 12.8 54.77 91.41 11.45 3.86 91 57 3 143 100 14 1.8 " 28 18.6 10.9 58.98 96.27 3.34 1.14 93 59 3 154 107 15 4.2 " 28.8 18.6 10.1 60.65 98.32 0 0 99 65 4 151 106 15 4.8 ** Sample after rolling overnight at 65.5 C with 8.559 g/1 BARACARB added.

*** Data in parentheses are the average of two separate sample evaluations.

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 a 1.39 kg/l 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 1.39 kg/l solution. Also, solutions containing solid calcium chloride require a larger concentration of ZnBr2 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 65.5"C with and without the addition of 8.559 g/l BARACARB. The data are given in Table 9.

Table 9 4.2795 g/1. NATROSOL 250 HHR API RHEOLOGY After Composition of Solution After Rolling * ** 2.301 1.390 1.702 95% 16 Hours API API Density % % % kg/1. kg/1. kg/1. CaCl2 Initial @ 65.5 C Fluid Fluid kg/1. ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. 600 300 600 300 Loss Loss 1.917 22 11.7 31.0 51.11 19.08 78.85 26.92 40 20 54 27 0.2 0.4 " 24 11.6 29.1 55.80 24.48 69.95 23.88 46 25 116 68 0 0 " 26 11.6 27.2 60.41 29.89 61.04 20.88 50 26 87 53 12 3.8 " 28 11.6 25.2 65.02 35.29 52.14 17.84 60 33 121 79 50 11 1.977 26 9.5 31.4 62.32 9.38 77.58 26.42 63 33 193 133 0 1.0 " 28 9.5 29.4 67.09 14.94 68.36 23.34 87 50 179 120 6.2 6.2 " 30 9.5 27.5 71.85 20.67 59.06 20.16 101 61 211 148 82 8.4 " 32 9.5 25.5 76.70 26.31 49.76 17.03 112 70 223 160 82 14.2 " 34 9.5 23.6 81.47 31.87 40.54 13.89 116 74 220 160 97 16.5 2.037 30.6 7.6 30.8 75.51 2.38 72.01 24.56 84 48 162 106 10 3.4 " 32 7.6 29.5 79.01 6.36 65.50 22.34 91 53 159 105 26 6.6 " 34 7.5 27.5 83.94 12.00 56.04 19.11 106 64 213 148 146 11.4 " 36 7.5 25.6 88.86 16.04 46.42 15.89 124 78 239 171 116 18.2 " 38 7.5 23.6 93.79 23.69 36.88 12.62 126 80 212 152 NC 17.8 2.097 37.2 5.7 28.1 94.27 1.91 55.80 19.02 95 55 172 112 95 7.4 " 38 5.6 27.4 96.57 4.13 51.82 17.66 101 60 248 175 112 14.9 " 40 5.6 25.4 101.66 10.02 41.97 14.35 118 73 240 172 95 17.9 " 42 5.6 23.4 106.75 16.06 32.11 10.99 140 91 224 162 109 20.4 2.157 44 3.9 25.0 115.01 3.02 36.40 12.39 158 101 234 169 63 16.6 " 46 3.9 23.0 120.26 9.22 26.23 8.94 216 148 226 162 65 19.1 * Sample after rolling @ 65.5 C.

** Sample after rolling @ 65.5 C with 8.559 g/1. BARACARB added.

As can be seen from the data in Table 9, brine solutions having a density of from about 1.917 to 2.037 kg/l 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 23"C and the API rheology obtained.

Thereafter, the API rheology and fluid loss were obtained after rolling the solutions at 23"C for 16 hours and after further rolling of the solutions an additional 1 6 hours at 65.5"C. The data are given in Table 1 0.

Table 10 4.2795 g/1. NATROSOL 250 HHR Composition of Brine 1 Hr. @ 23 C 16 Hr. @ 23 C 16 Hr. @ 16.5 C 2.301 1.390 1.702 95% API API API Density % % % kg/1. kg/1. kg/1. CaCl2 H2O Rheology* Rheology Fluid Rheology Fluid kg/1. ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg. litre AV PV YP GS AV PV YP GS Loss AV PV YP GS Loss 1.726 20.0 7.0 29.8 41.81 36.72 69.23 0 9.30 34 26 16 2 47 31 32 6 8 57 37 40 15 4 " 26.0 18.7 11.4 54.05 97.69 7.23 0 0 44 31 26 3 64 42 45 11 15 74 45 58 15 5 1.750 20.4 7.8 28.8 43.24 41.49 66.61 0 7.63 28 22 12 2 46 31 30 6 8 55 39 33 18 4 " 24.0 13.8 19.7 50.87 73.21 34.89 0 0 32 26 13 1 58 39 38 9 5 67 42 51 13 7 1.773 21.2 9.4 27.4 45.54 50.87 62.55 0 0 18 17 2 0 46 34 24 5 5 56 39 34 19 2 " 23.2 11.0 24.1 49.92 59.14 49.92 0 0 37 30 15 1 65 42 46 12 7 75 45 61 16 7 " 25.0 12.4 21.1 53.73 66.77 38.47 0 0 38 29 19 2 68 43 50 12 14 76 47 59 16 11 1.797 22.0 7.9 29.1 47.93 43.24 67.80 0 0 24 22 5 0 54 37 34 8 2 66 40 52 12 4 " 24.0 9.5 25.8 52.30 51.67 55.00 0 0 38 29 18 2 68 43 51 13 13 76 43 67 17 5 " 26.0 11.0 22.4 56.67 60.17 42.13 0 0 44 32 24 2 68 42 53 13 11 80 48 65 18 15 1.821 22.8 6.4 30.7 50.31 35.61 73.05 0 0 41 30 22 2 62 40 44 12 12 70 43 55 10 11 " 24.8 8.0 27.4 54.77 44.11 60.09 0 0 57 39 37 6 80 47 66 19 16 85 37 96 26 12 " 26.8 9.5 24.1 59.14 52.62 47.21 0 0 54 37 35 5 74 44 60 16 24 81 47 69 21 23 1.845 23.6 5.0 32.3 52.78 28.14 78.05 0 0 40 30 20 3 65 40 51 13 17 74 42 64 9 10 " 25.6 6.6 28.9 57.23 36.80 64.94 0 0 56 40 33 6 86 51 70 19 12 88 48 80 22 17 " 27.6 8.1 25.7 61.76 45.23 51.98 0 0 68 46 45 8 83 46 75 22 12 96 51 90 27 18 1.869 24.4 3.7 33.7 55.32 20.83 82.82 0 0 49 33 32 4 71 42 58 15 21 77 40 74 19 16 " 26.4 5.2 30.4 59.85 29.33 69.79 0 0 56 35 43 7 79 45 68 19 12 87 47 81 21 14 " 28.4 6.7 27.1 64.38 38.15 56.43 0 0 64 43 42 8 81 46 71 20 27 88 48 81 23 14 1.893 25.2 2.3 35.1 57.87 13.43 87.67 0 0 52 34 36 5 77 43 69 18 35 82 43 79 22 48 " 27.2 3.9 31.8 62.40 22.34 74.24 0 0 61 41 41 8 83 45 77 23 26 91 49 85 26 33 " 29.2 5.4 28.5 67.00 31.08 60.89 0 0 66 44 44 10 89 49 80 24 37 91 49 84 25 27 1.917 26.0 1.0 36.5 60.41 6.12 92.44 0 0 54 33 42 6 73 40 67 18 83 81 43 77 23 120 " 28.0 2.6 33.1 65.10 15.18 78.69 0 0 67 45 44 9 84 44 81 25 21 96 50 93 29 83 " 30.0 4.1 29.8 69.71 24.00 65.26 0 0 69 45 48 11 88 46 85 24 47 95 53 85 30 60 * AV = Apparent Viscosity ; PV = Plastiv Viscosity ; YP = Yield Point; GS = 10-Second 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 33.38(D-1.138)% wherein D is the density of the solution in the kg/l. Preferably, the zinc concentration is greater than 33.38(D-1.138)% more preferably greater than 33.38(D-1.019)%.

Claims (28)

1. A thickened brine solution having a density in the range of from about 1.702 to 2.1 57 kg/litre which comprises water, at least 20 weight percent of zinc bromide, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose.

2. A brine solution as claimed in Claim 1 wherein said solution has a density of from 1.702 to 1.869 kg/litre and said calcium bromide is present in an amount from 14.5 to 41.3 weight percent.

3. A brine solution of Claim 2 wherein the amount of zinc bromide is from 20 to 46.9 weight percent.

4. A brine solution as claimed in Claim 1 which comprises up to (2x-33) weight percent of calcium chloride wherein x is the weight percent zinc bromide.

5. A brine solution as claimed in Claim 4 wherin said solution has a density of from 1.702 to 1.869 kg/litre and wherein calcium chloride is present in an amount of from 0.1 to 20 weight percent and calcium bromide is present in an amount of from 9.4 to 42 weight percent.

6. A brine solution as claimed in Claim 5 wherein the zinc bromide is present in an amount of from 20 to 37 weight percent.

7. A brine solution as claimed in Claim 4 wherein said solution has a density in the range of from 1.869 to 2.037 kg/litre and wherein calcium chloride is present in an amount of from about 0.1 to about 1 3.5 weight percent, said calcium bromide is present in an amount of from 1 2.9 to 41.3 weight percent, and said zinc bromide is present in an amount of at least (71.518D-113.7) weight percent, wherein D is the density of said brine solution in kg/litre.

8. A brine solution as claimed in Claim 7 containing up to 50 weight percent zinc bromide.

9. A brine solution as claimed in any preceding Claim wherein the hydroxyethyl cellulose is activated.

10. A brine solution as claimed in Claim 1 and substantially as hereinbefore described with reference to any of the Examples.

11. A method of preparing a thickened brine solution according to any of Claims 1 to 9 which comprises mixing an aqueous solution having a density in the range of from 1.702 to 2.157 kg/litre and which comprises water, at least 20 weight percent of zinc bromide and calcium bromide, with a viscosifying amount of hydroxyethyl cellulose.

1 2. A method as claimed in Claim 11 wherein the aqueous solution contains up to (2x-33) weight percent of calcium chloride wherein x is the weight percentage of zinc bromide and has a density in the range of from 1.869 to 2.037 kg/litre and has a zinc bromide concentration of at least (71.518D-113.7) weight percent wherein D is the density of said aqueous solution in kg/litre.

1 3. A method as claimed in Claim 11 wherein said aqueous solution has a density in the range of from 1.702 to 1.821 kg/litre and contains from 14.5 to 39.5 weight percent of calcium bromide.

14. A method as claimed in Claim 11 wherein said aqueous solution has a density in the range of from 1.821 to 1.917 kg/litre and contains from

15.9 to 39.5 weight percent of calcium bromide and at least (47.985D-67.4) weight percent of zinc bromide wherein D is the density of said brine solution in kg/litre.

1 5. A method as claimed in Claim 14 wherein said aqueous solution has a density in the range of from 1.917 to 2.157 kg/litre and contains from 16.9 to 38.8 weight percent of calcium bromide, and at least (w) (p) (D-d) weight weigh percent of (D) (w-d) zinc bromide wherein w is the density in ppg of a solution A containing zinc bromide, p is the percent by weight zinc bromide in solution A, d is the density in ppg of a solution B containing only calcium bromide which is mixed with solution A, and D is the density in ppg of said aqueous solution.

16. A method as claimed in Claim 11 wherein said aqueous solution has a density in the range of from 1.738 to 1.983 kg/litre and contains from 0.1 to 20 weight percent of calcium chloride, from 9.4 to 33.8 weight percent of calcium bromide, and at least 33.38(D-1.138) weight percent of zinc bromide wherein D is the density of said aqueous solution in kg/litre.

1 7. A process as claimed in Claim 1 6 wherein the concentration of zinc bromide is at least 33.38(D-1.078) weight percent and wherein the density of the aqueous solution is in the range of from 1.702 to 2.037 kg/litre.

18. A method as claimed in Claim 1 6 wherein the concentration of zinc bromide is at least 33.38(D-1.019) weight percent and wherein the density of said aqueous solution is in the range of from 1.702 to 2.091 kg/litre.

1 9. A method as claimed in Claim 1 3 wherein the concentration of zinc bromide is from 20 to 45 weight percent.

20. A method as claimed in Claim 14 wherein the concentration of zinc bromide is from 20 to 48 weight percent.

21. A method as claimed in Claim 15 wherein the concentration of zinc bromide is from 24.6 to 50 weight percent.

22. A method as claimed in Claim 1 6 wherein the concentration of zinc bromide is from 20.8 to 50 weight percent.

23. A method as claimed in Claim 1 7 wherein the concentration of zinc bromide is from 22.8 to 50 weight percent.

24. A method as claimed in Claim 1 8 wherein the concentration of zinc bromide is from 24.8 to 50 weight percent.

25. A method as claimed in Claim 11 wherein said aqueous solution has a density in the range of from 1.702 to 1.738 kg/litre and contains from 0.1 to 20 weight percent of calcium chloride, and from 9.4 to 34.6 weight percent of calcium bromide.

26. A method as claimed in any of Claims 11 to 25, wherein said hydroxyethyl cellulose is activated.

27. A method as claimed in any of Claims 11 to 24, wherein said mixing is carried out at elevated temperatures.

28. A method as claimed in Claim 11 and substantially as hereinbefore described with reference to any of the Examples.