GB2121092A - Thickened heavy brines - Google Patents

Abstract

Thickened heavy brines can be obtained having a density of 1.869 to 2.037 kg/litre which comprise water, at least 20 weight percent of zinc bromide, calcium chloride, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose, and wherein said calcium chloride is present in an amount of from 0.1 to 13.5 weight percent, said calcium bromide is present in an amount of from 12.9 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. 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 cailed heavy brines having a density between 1.869 and 2.037 kg/litre.

Hydroxyethyl cellulose (HEC) is used as a viscosifier 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.

The present invention provides a thickened brine solution having a density in the range of between 1.869 and 2.037 kg/litre which comprises water, at least 20 weight percent of zinc bromide, calcium chloride, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose, and wherein said calcium chloride is present in an amount of from 0.1 to 13.5 weight percent, said calcium bromide is present in an amount of from 12.9 to 41.3 weight percent, and said zinc bromide is present in an amount of at least (71.51 8D-1 13.7) weight percent, wherein D is the density of said brine solution in kg/litre.

In another embodiment, the present invention provides a method of preparing a thickened brine solution as defined above which comprises mixing an aqueous solution having a density in the range of from 1.869 and 2.1 57 kg/litre and which comprises water, at least 20 weight percent of zinc bromide, calcium chloride, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose, and wherein said calcium chloride is present in an amount of from 0.1 to 13.5 weight percent, said calcium bromide is present in an amount of from 12.9 to 41.3 weight percent, and said zinc bromide is present in an amount of at least (71.51 8D-1 13.7) weight percent, wherein D is the density of said brine solution in kg/litre 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 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 calcium chloride are employed depending upon the desired density and the desired temperature of crystallization of the brine. We have found that the presence 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.

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 illustrate more fully the present invention, the foliowing 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 1 3B, 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 bkg/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% CaCI2 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 Multimixerfor 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 65.50C to determine the final viscosity.The data obtained are given in Table 1.

Table 1 Composition of solution 8.559 g/l Natrosol 250 hhr Fann 300 rpm reading 2.301 1.390 1.702 95% Density % % % kg/l kg/l kg/l CaCl2 After rolling kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg lnitial 16 hr @ 65.5 C* 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 29.8 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 27.83 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 3.71 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 solid calcium chloride. The brine solutions were mixed on a Multi mixer 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 65.50C, 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/l Natrosol 250 hhr 2.301 1.390 1.702 95% Fann 300 rpm reading Density % % % kg/l kg/l kg/l CaCl2 After rolling kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg lnitial 16 hr @ 65.5 C 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 18.21 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 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 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 48.98 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 data in Table 2, the solubilization of the HEC is different in CaBr2/ZnBr2 solutions as opposed to CaCI2/CaBrlZnBr2 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 CaBr2/ZnBr2 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 CaBrlZnBr2 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 Multi mixer 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 4.2 795 gll Natrosol 250 hhr After rolling Composition of solution lnitial 16 hours (B 65.50C API rheology API rheology APl(1) % % % Density fluid ZnBr2 Cay12 CaBr2 kg/l 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 31 251 179 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 O 0 53 1.70 155 115 19 152 113 16 17.5 O 0 53 1.70 154 115 18 158 117 16 (1) Sample after rolling with 8.559 g/l 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 65.50C and cooling to room temperature. The data are given in Tables 4 and 5.

4.2795 g/l Natrosol 250 hhr APl rheology Composition of solution After rolling 2.301 1.390 1.702 lnitial 16 hr @ 65.5 C AP(1) % % % Density kg/l kg/l kg/l fluid ZnBr2 CaCl2 CaBr2 kg/l (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 39.42 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 13 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 18.9 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 Table 4 (contd.) 4.2795 g/l natrosol 250 hhr APl rheology Composition of solution After rolling 2.301 1.390 1.702 lnitial 16 hr @ 65.5 C APl (1) % % % Density kg/l kg/l kg/l fluid ZnBr2 CaCl2 CaBr2 kg/l (litre) (litre) (litre) 600 300 3 600 300 3 loss 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 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 98.40 176 129 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/l Baracarb added.

Table 5 4.2795 g/l Natrosol 250 hhr APl rheology Composition of solution After rolling 2.301 1.390 1.702 lnitial 16 hr @ 65.5 C APl (1) % % % Density kg/l kg/l kg/l fluid ZnBr2 CaCl2 CaBr2 kg/l (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 0 108.58 158 116 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 11.31 107.94 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 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 15 114 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 42.92 77.58 25 13 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/l Natrosol 250 hhr APl rheology Composition of solution After rolling 2.301 1.390 1.702 lnitial 16 hr @ 65.5 C APl (1) % % % Density kg/l kg/l kg/l fluid ZnBr2 CaCl2 CaBr2 kg/l (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/l 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 (2x33)% 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 65.50 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/l natrosol 250 hhr APl rheology*** Composition of solution APl After one After rolling fluid 2.301 1.390 1.702 95% hour @ 23 C overninght @ 65.5 C loss Ref. Density % % % kg/l kg/l kg/l CaCl2 ** No. kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg 600 300 3 600 300 3 *** Vl-1 1.738 24 18.6 14.8 50.55 86.48 19.55 6.58 51 28 1 102 59 2 0 2 " 26 18.6 12.8 54.77 91.41 11.45 3.86 91 57 3 143 100 14 1.8 3 " 24 14.9 18.1 50.55 78.85 29.57 0 75 47 2 134 90 12 2.0 4 " 26 16.6 14.5 54.77 87.75 16.45 0 (83) (53) (3) (137) (96) (14) (3.2) 5 " 28 18.6 10.9 58.98 96.27 3.34 1.14 93 59 3 154 107 15 4.2 6 " 28 18.0 11.5 58.98 94.98 5.01 0 91 58 3 145 100 14 3.4 7 " 28.8 18.6 10.1 60.65 98.32 0 0 99 65 4 151 106 15 4.8 Vl-8 1.797 24 16.1 19.9 52.30 65.81 36.25 12.26 41 21 0 73 38 1 0.1 9 " 26 16.1 18.0 56.59 70.74 28.14 9.49 (62) (35) (1) (159) (125) (20) (0.7) 10 " 28 16.1 16.0 61.04 76.15 19.39 6.54 73 43 1 152 109 16 2.6 11 " 24 9.5 25.8 52.30 51.67 55.00 0 82 51 3 148 104 17 1.2 12 " 26 10.9 22.5 56.59 59.85 42.52 0 (102) (71) (4) (156) (111) (19) (5.0) 13 " 30 16.1 14.0 65.34 81.07 11.13 3.77 89 57 3 179 127 21 3.8 14 " 28 12.5 12.5 61.04 68.52 29.41 0 98 64 4 132 95 12 6.0 15 " 32 16.1 12.1 69.71 86.16 2.70 0.91 140 91 9 191 138 23 5.0 16 " 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/l Natrosol 250 hhr APl rheology*** Composition of solution APl After one After rolling fluid 2.301 1.390 1.702 95% hour @ 23 C overnight @ 65.5 C loss Ref.Density % % % kg/l kg/l kg/l CaCl2 ** No. kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg 600 300 3 600 300 3 *** Vl-17 1.857 24 13.9 24.6 54.05 45.31 53.10 18.21 45 23 1 73 38 2 0 18 " 26 13.9 22.8 58.50 50.23 44.67 15.35 (68) (40) (2) (190) (143) (19) (4.0) 19 " 28 13.7 20.7 63.03 55.64 35.77 12.08 95 58 3 160 148 23 6.0 20 " 24 4.4 32.9 54.05 24.64 80.28 0 92 59 3 140 118 22 1.4 21 " 30 13.7 18.8 67.56 60.89 27.18 9.17 (103) (66) (3) (184) (26) (24) 22 " 26 5.8 29.8 58.50 32.83 67.64 0 (106) (71) (4) (160) (118) (21) (7.5) 23 " 28 7.4 26.4 63.03 41.65 54.29 0 105 70 5 149 109 17 5.6 24 " 32 13.7 16.9 72.01 66.13 18.60 6.27 (124) (82) (6) (193) (140) (26) (23) 25 " 34 13.7 14.9 76.54 71.54 9.62 3.27 127 82 7 185 135 21 11 26 " 36.2 13.7 12.7 81.55 77.42 0 0 162 111 15 185 135 22 10 Vl-27 1.917 24.6 11.7 28.5 57.23 26.23 67.16 22.97 91 52 1 132 73 2 0 28 " 26 11.6 27.2 60.41 29.89 61.04 20.88 (65) (36) (1) (197) (17) (2.0) 29 " 28 11.6 25.3 65.02 35.13 52.30 17.89 80 46 2 144 130 14 4.0 30 " 30 11.6 23.3 69.71 40.86 43.08 14.80 90 54 2 180 138 19 11.4 31 " 24.6 0 38.7 57.23 0 101.74 0 135 91 11 166 120 24 13 32 " 32 11.5 21.3 74.40 46.42 33.94 11.44 90 55 3 220 156 25 33 " 26 1.0 36.5 60.41 6.04 92.52 0 113 76 6 167 123 22 57 34 " 28 2.5 33.2 65.02 14.78 79.17 0 129 88 8 175 127 23 36 35 " 34 11.5 21.3 79.01 25.67 25.12 8.49 94 59 3 202 146 25 21 36 " 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/l Baracarb added.

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

Table 7 4.2795 g/l Natrosol 250 hhr APl rheology *** Composition of solution APl After one After rolling fluid 2.301 1.390 1.702 95% hour @ 23 C ovemight @ 65.5 C loss Ref. Density % % % kg/l kg/l kg/l CaCl2 ** No. kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg 600 300 3 600 300 3 *** Vll-1 1.917 24.6 0 38.7 57.23 0 101.74 0 135 91 11 166 120 24 13 2 1.857 24 4.4 32.9 54.05 24.64 80.28 0 92 59 3 140 118 22 1.4 3 1.797 24 9.5 25.8 52.30 51.67 55.00 0 82 51 3 148 104 17 1.2 4 1.738 24 14.9 18.1 50.55 78.85 29.57 0 75 47 2 134 90 12 2.0 5 1.917 24.6 11.7 28.5 57.23 26.23 67.16 22.97 91 52 1 132 73 2 0 6 1.857 24 13.9 24.6 54.05 45.31 53.10 18.20 45 23 1 73 38 2 0 7 1.797 24 16.1 19.9 52.30 65.81 36.25 12.26 41 21 0 73 38 1 0.1 8 1.738 24 18.6 14.8 50.55 86.48 19.55 6.58 51 28 1 102 59 2 0 Vll-9 1.917 26 1.0 36.5 60.41 6.04 92.52 0 113 76 6 167 123 22 57 10 1.857 26 5.8 29.8 58.50 32.83 67.64 0 (106) (71) (4) (160) (118) (21) (7.5) 11 1.797 26 10.9 22.5 56.60 59.85 42.52 0 (102) (71) (4) (156) (111) (19) (5.0) 12 1.738 26 16.6 14.5 54.77 87.75 16.45 0 (83) (53) (3) (137) (96) (14) (3.2) 13 1.917 26 11.6 27.2 60.41 29.89 61.04 20.88 (65) (36) (1) (197) (149) (17) (2.0) 14 1.857 26 13.9 22.8 58.50 50.23 44.67 16.25 (68) (40) (2) (190) (143) (19) (4.0) 15 1.797 26 16.1 18.0 56.60 70.74 28.14 9.49 (62) (35) (1) (169) (125) (20) (0.7) 16 1.738 26 18.6 12.8 54.77 91.41 11.45 3.86 91 57 3 143 100 14 1.8 Table 7 (contd.) 4.2795 g/l natrosol 250 hhr APl rheology *** Composition of solution APl After one After rolling fluid 2.301 1.390 1.702 95% hour @ 23 C overnight @ 65.5 C loss Ref.Density % % % kg/l kg/l kg/l CaCl2 ** No. kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg 600 300 3 600 300 3 *** Vll-17 1.917 28 2.5 33.2 65.02 14.78 79.17 0 129 88 8 175 127 23 36 18 1.857 28 7.4 26.4 63.03 41.65 54.29 0 105 70 5 149 109 17 5.6 19 1.917 28 11.6 25.3 65.02 35.13 52.30 17.89 80 46 2 144 130 14 4.0 20 1.797 28 12.5 19.1 61.04 68.52 29.52 0 98 64 4 132 95 12 6.0 21 1.857 28 13.7 20.7 63.03 55.64 35.77 12.08 95 58 3 160 148 23 6.0 22 1.797 28 16.1 16.0 61.04 76.15 19.39 6.54 73 43 1 152 109 16 2.6 23 1.738 28 18.0 11.5 58.98 94.98 5.01 0 91 58 3 145 100 14 3.4 24 1.738 28 18.6 10.9 58.98 96.27 3.34 1.14 93 59 3 154 107 15 4.2 25 1.738 28.8 18.6 10.1 60.65 98.32 0 0 99 65 4 151 106 15 4.8 Vll-26 1.917 30 11.6 13.3 69.71 40.86 43.08 14.80 90 54 2 180 138 19 11 27 1.857 30 13.7 18.8 67.56 60.56 60.89 27.18 9.17 (103) (66) (3) (184) (146) (26) (24) 28 1.797 30 16.1 14.0 65.34 81.07 11.13 3.77 89 57 3 179 127 21 3.8 Vll-29 1.917 32 11.5 21.3 74.40 46.42 33.94 11.44 90 55 3 220 156 25 22 30 1.857 32 13.7 16.9 72.01 66.13 18.60 6.27 (124) (82) (6) (193) (140) (26) (23) 31 1.797 32 16.1 12.1 69.71 86.16 2.70 0.91 140 91 9 191 138 23 5.0 32 1.797 32.6 16.1 11.5 71.12 87.85 0 0 128 87 9 175 124 20 95 Vll-33 1.917 34 11.5 19.4 79.01 51.67 25.12 8.49 94 59 3 202 146 25 21 34 1.857 34 13.7 14.9 76.54 71.54 9.62 3.27 127 82 7 185 135 21 11 Vll-35 1.857 36.2 13.7 12.7 81.55 77.42 0 0 162 111 15 185 135 22 10 Vll-36 1.917 39.6 11.5 13.9 92.04 66.93 0 0 (168) (116) (16) (184) (135) (23) (35) **Sample after rolling ovemight at 65.5 C with 8.559 g/l Baracarb added.

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

Table 8 4.2795 g/l natrosol 250 hhr APl rheology *** Composition of soultion APl After After folling fluid 2.301 1.390 1.702 95% hour @ 23 C overnight @ 65.5 C loss Ref. Density % % % kg/l kg/l kg/l CaCl2 ** No. kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg 600 300 3 600 300 3 *** Vlll-1 1.917 24.6 11.7 28.5 57.23 26.23 67.16 22.97 91 52 1 132 73 2 0 2 " 26 11.6 27.2 60.41 29.89 61.04 20.88 (65) (36) (1) (197) (149) (17) (2.0) 3 " 28 11.6 25.3 65.02 35.13 52.30 17.89 80 46 2 144 130 14 4.0 4 " 30 11.6 23.3 69.71 40.86 43.08 14.80 90 54 2 180 138 19 11 5 " 32 11.5 21.3 74.40 46.42 33.94 11.44 90 55 3 220 156 25 22 6 " 34 11.5 19.4 79.01 51.67 25.12 8.48 94 59 3 202 146 25 21 7 " 39.6 11.5 14.9 92.04 66.93 0 0 (168) (116) (16) (184) (135) (23) (35) Vll-8 1.857 24 13.9 24.6 54.05 45.31 53.10 18.21 45 23 1 73 38 2 0 9 " 26 13.9 22.8 58.50 50.23 44.67 15.35 (68) (40) (2) (190) (143) (19) (4.0) 10 " 28 13.7 20.7 63.03 55.64 35.77 12.08 95 58 3 160 148 23 6.0 11 " 30 13.7 18.8 67.56 60.89 27.18 9.17 (103) (66) (3) (184) (146) (26) (24) 12 " 32 13.7 16.9 72.01 66.13 18.60 6.27 (124) (82) (6) (193) (140) (26) (23) 13 " 34 13.7 14.9 76.54 71.54 9.62 3.27 127 82 7 185 21 11 14 " 36.2 13.7 12.7 81.5 77.42 0 0 162 111 15 185 135 22 10 Vll-15 1.797 24 16.1 19.9 52.30 65.81 36.25 12.62 41 21 0 73 38 1 0.1 16 " 26 16.1 18.0 56.59 70.74 28.14 9.49 (62) (35) (1) (159) (20) (0.7) 17 " 28 16.1 16.0 61.04 76.15 19.39 6.54 73 43 1 15.2 109 16 2.6 18 " 30 16.1 14.0 65.34 81.07 11.13 3.77 89 57 3 179 127 21 3.8 19 " 32 16.1 12.1 69.71 86.16 2.70 0.91 140 91 9 191 138 23 5.0 20 " 32.6 16.1 11.5 71.12 87.85 0 0 128 87 9 175 124 20 95 Vll-21 1.738 24 18.6 14.8 50.55 86.48 19.55 6.58 51 28 1 102 59 2 0 22 " 26 18.6 12.8 54.77 91.45 11.45 3.86 91 57 3 143 100 14 1.8 23 " 28 18.6 10.9 58.98 96.27 3.34 1.14 93 59 3 154 107 15 4.2 24 " 28.8 18.6 10.1 60.65 98.65 98.32 0 0 99 65 4 151 106 15 4.8 **Sample after rolling overnight at 65.5 C g/l 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 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 1 6 hours at 65.50C with and without the addition of 8.559 g/l Baracarb. The data are given in Table 9.

Table 9 4.2795 g/l natrosol 250 hhr APl rheology After Composition of solution rolling 16 hours * ** 2.301 1.390 1.702 95% lnitial @ 65.5 C APl APl Ref. Density % % % kg/l kg/l kg/l CaCl2 fluid fluid No. kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg 600 300 600 300 loss loss IX-1 1.917 22 11.7 31.0 51.11 19.08 78.85 26.92 40 20 54 27 0.2 0.4 2 " 24 11.6 29.1 55.80 24.48 69.95 23.88 46 25 116 68 0 0 3 " 26 11.6 27.2 60.41 29.89 61.04 20.88 50 26 87 53 12 3.8 4 " 28 11.6 25.2 65.02 35.02 52.14 17.84 60 33 121 79 50 11 lX-5 1.977 26 9.5 31.4 62.32 77.58 26.42 63 33 193 133 0 1.0 6 " 28 9.5 29.4 67.09 14.94 68.36 23.34 87 50 179 120 6.2 6.2 7 " 30 9.5 27.5 71.85 20.67 59.06 20.16 101 61 211 148 82 8.4 8 " 32 9.5 25.5 76.70 26.31 49.76 17.03 112 70 223 160 82 14.2 9 " 34 9.5 23.6 81.47 31.87 40.54 13.89 116 74 220 160 97 16.5 lX-10 2.037 30.6 7.6 30.8 75.51 2.38 72.01 24.56 84 48 162 106 10 3.4 11 " 32 7.6 29.5 79.01 6.36 65.50 22.34 91 53 159 105 26 6.6 12 " 34 7.5 27.5 83.94 12.00 56.04 19.11 106 64 213 148 146 11.4 13 " 36 7.5 25.6 88.86 16.06 46.42 15.89 124 78 239 171 116 18.2 14 " 38 7.5 23.6 93.79 23.69 36.88 12.62 126 80 212 152 NC 17.8 lX-15 2.097 37.2 5.7 28.1 94.27 1.91 55.80 19.02 95 55 172 112 95 7.4 16 " 38 5.6 27.4 96.57 4.13 51.82 17.66 101 60 248 175 112 14.9 17 " 40 5.6 25.4 101.66 10.02 41.97 14.35 118 73 240 172 95 17.9 18 " 42 5.6 23.4 106.75 16.06 32.11 10.99 140 91 224 162 109 20.4 lX-19 2.157 44 3.9 25.0 115.01 3.02 36.40 12.39 158 101 234 169 63 16.6 20 " 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 @ 65.6 C with 8.559 g/l 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 kgjl 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 230C and the API rheology obtained. Thereafter, the API rheology and fluid loss were obtained after rolling the solutions at 230C for 16 hours and after further rolling of the solutions an additional 16 hours at 65.50C. The data are given in Table 10.

Table 10 Composition of brine 2.301 1.390 1.702 95% Ref. Density % % % kg/l kg/l kg/l CaCl2 H2O No. kg/l ZnBr2 CaCl2 CaBr2 (litre) (litre) (litre) kg litre X-1 1.726 20.0 7.0 29.8 41.81 36.72 69.23 0 9.30 2 " 26.0 18.7 11.4 54.05 97.69 7.23 0 0 X-3 1.750 20.4 7.8 28.8 43.24 41.49 66.61 0 7.63 4 " 24.0 13.8 19.7 50.87 73.21 34.89 0 0 X-5 1.773 21.2 9.4 27.4 45.54 50.87 62.55 0 0 6 " 23.2 11.0 24.1 49.92 59.14 49.92 0 0 7 " 25.0 12.4 21.1 53.73 66.77 38.47 0 0 X-8 1.797 22.0 7.9 29.1 47.93 43.24 67.80 0 0 9 " 24.0 9.5 25.8 52.30 51.67 55.00 0 0 10 " 26.0 11.0 22.4 56.67 60.17 42.13 0 0 X-11 1.821 22.8 6.4 30.7 50.31 35.61 73.05 0 0 12 " 24.8 8.0 27.4 54.77 44.11 60.09 0 0 13 " 26.8 9.5 24.1 59.14 52.62 47.21 0 0 X-14 1.845 23.6 5.0 32.3 52.78 28.14 78.05 0 0 15 " 25.6 6.6 28.9 57.23 36.80 64.94 0 0 16 " 27.6 8.1 25.7 61.76 45.23 51.98 0 0 X-17 1.869 24.4 3.7 33.7 55.32 20.83 82.82 0 0 18 " 26.4 5.2 30.4 59.85 29.33 69.79 0 0 19 " 28.4 6.7 27.1 64.38 38.15 56.43 0 0 X-20 1.893 25.2 2.3 35.1 57.87 13.43 87.67 0 0 21 " 27.2 3.9 31.8 62.40 22.34 74.24 0 0 22 " 29.2 5.4 28.5 67.00 31.08 60.89 0 0 X-23 1.917 26.0 1.0 36.5 60.41 6.12 92.44 0 0 24 " 28.0 2.6 33.1 65.10 15.18 78.69 0 0 25 " 30.0 4.1 29.8 69.71 24.00 65.26 0 0 Table 10 (contd.) 4.2795 g/l Natrosol 250 hhr 1 hr @ 23 C 16 hr @ 23 C 16 hr @ 16.5 C APl rheology* APl rheology APl rheology Ref. Fluid Fluid No.AV PV YP GS AV PV YP GS loss AV PV YP GS loss X-1 34 26 16 2 47 31 32 6 8 57 37 40 15 4 2 44 31 26 3 64 42 45 11 15 74 45 58 15 5 X-3 28 22 12 2 46 31 30 6 8 55 39 33 18 4 4 32 26 13 1 58 39 38 9 5 67 42 51 13 7 X-5 18 17 2 0 46 34 24 5 5 56 39 34 19 2 6 37 30 15 1 65 42 46 12 7 75 45 61 16 7 7 38 29 19 2 68 43 50 12 14 76 47 59 16 11 X-8 24 22 5 0 54 37 34 8 2 66 40 52 12 4 9 38 29 18 2 68 43 51 13 13 76 43 67 17 5 10 44 32 24 2 68 42 53 13 11 80 48 65 18 15 X-11 41 30 22 2 62 40 44 12 12 70 43 55 10 11 12 57 39 37 6 80 47 66 19 16 85 37 96 26 12 13 54 37 35 5 74 44 60 16 24 81 47 69 21 23 X-14 40 30 20 3 65 40 51 13 17 74 42 64 9 10 15 56 40 33 6 86 51 70 19 12 88 48 80 22 17 16 68 46 45 8 83 46 75 22 12 96 51 90 27 18 X-17 49 33 32 4 71 42 58 15 21 77 40 74 19 16 18 56 35 43 7 79 45 68 19 12 87 47 81 21 14 19 64 43 42 8 81 46 71 21 27 88 48 81 23 14 X-20 52 34 36 5 77 43 69 18 82 43 79 22 48 21 61 41 41 8 83 45 77 23 26 91 49 85 26 33 22 66 44 44 10 89 49 80 24 37 91 49 84 25 27 X-23 54 33 42 6 73 40 67 18 83 81 43 77 23 120 24 67 45 44 9 84 44 81 25 21 96 50 93 29 83 25 69 45 48 11 88 46 85 24 47 95 53 85 30 60 *AV=Apparent Viscosity; PV=Plastic Viscosity; YP=Yield Plint; 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 .1 38)% wherein D is the density of the solution in the kg/l. Preferably, the zinc concentration is greater than 33.38(D-1 .1 38)% more preferably greater than 33.38(D-1 .01 9)%.

Claims (19)

Claims

1. A thickened brine solution having a density in the range of between 1.869 and 2.037 kg/litre which comprises water, at least 20 weight percent of zinc bromide, calcium chloride, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose, and wherein said calcium chloride is present in an amount of from 0.1 to 13.5 weight percent, said calcium bromide is present in an amount of from 12.9 to 41.3 weight percent, and said zinc bromide is-present in an amount of at least (71.51 8D-1 13.7) weight percent, wherein D is the density of said brine solution in kg/litre.

2. A brine solution as claimed in Claim 1 containing up to 50 weight percent zinc bromide.

3. A brine solution as claimed in Claim 1 or 2, wherein the hydroxyethyl cellulose is activated.

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

5. A method of preparing a thickened brine solution according to any of Claims 1 to 3 which comprises mixing an aqueous solution having a density in the range of from 1.869 and 2.1 57 kg/litre and which comprises water, at least 20 weight percent of zinc bromide, calcium chloride, calcium bromide, and a viscosifying amount of hydroxyethyl cellulose, and wherein said calcium chloride is present in an amount of from 0.1 to 13.5 weight percent, said calcium bromide is present in an amount of from 12.9 to 41.3 weight percent, and said zinc bromide is present in an amount of at least (71.51 8D-1 1 3.7) weight percent, wherein D is the density of said brine solution in kg/litre with a viscosifying amount of hydroxyethyl cellulose.

6. A method as claimed in Claim 5, wherein the aqueous solution contains up to (2x-33) weight percent of calcium chloride wherein x is the weight percentage of zinc bromide.

7. A method as claimed in Claim 5, wherein said aqueous solution has a density between 1.869 and 1.917 kg/litre and contains from 1 5.9 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.

8. A method as claimed in Claim 7, wherein said aqueous solution has a density in the range of from 1.917 to 2.1 57 kg/litre and contains from 16.9 to 38.8 weight percent of calcium bromide, and at least (w) (p) (D-d) weight 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.

9. A method as claimed in Claim 5, wherein said aqueous solution has a density between 1.869 and 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.

10. A process as claimed in Claim 9, 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 between 1.869 and 2.037 kg/litre.

11. A method as claimed in Claim 9, 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 between 1.869 and 2.091 kg/litre.

12. A method as claimed in Claim 7, wherein the concentration of zinc bromide is from 20 to 48 weight percent.

13. A method as claimed in Claim 8, wherein the concentration of zinc bromide is from 24.6 to 50 weight percent.

14. A method as claimed in Claim 9, wherein the concentration of zinc bromide is from 20.8 to 50 weight percent.

1 5. A method as claimed in Claim 10, wherein the concentration of zinc bromide is from 22.8 to 50 weight percent.

1 6. A method as claimed in Claim 11, wherein the concentration of zinc bromide is from 24.8 to 50 weight percent.

17. A method as claimed in any of Claims 5 to 16, wherein said hydroxyethyl cellulose is activated.

1 8. A method as claimed in any of Claims 5 to 16, wherein said mixing is carried out at elevated temperatures.

19. A method as claimed in Claim 5 and substantially as hereinbefore described with reference to any of the Examples.