Approximate Maximum Density, !b/gal
Potassium chloridc (K.Ci) Sodium chloride (NaCl) Calcium chloridc (CaCE) Calcium bromide (CaBr,)
Calcium chloride/calcium bromide
Three-Salt Brines Calcium chloride/calcium bromide/zinc
The potassium ion is particularly effective at plugging the clay lattice to minimize hydration of formation clays, as shown in Fig. 8-7.
A sodium chloride system (NaCl) is probably the most common brine water used in drilling, completion, and workover operations due to its availability. The maximum density for a sodium chloride brine is 10.0 lb/gal at 60°F. Note that a density of 9.7 lb/gal is relatively easy to achieve. The range from 9.7 to 10.0 lb/gal requires special attention.
Calcium chloride mixtures are used commonly when densities from 9.7 to 11.6 lb/gal are required. The CaCh fluid is used in many workover and completion operations. The freezing (crystallization) point of an 11.6-Ib/gaJ CaCE brine is 44°F, which may cause operating difficulties at low surface temperatures.
Brine systems requiring densities to 15.1 lb/gal use a two-salt mixture of calcium chloride and calcium bromide (CaCl2 and CaBr,). The basic ingredient of this brine is a calcium bromide solution with a density of 14.1 to 14.3 lb/gal. The density can be increased to 15.1 lb/gal by adding calcium chloride flakes or pellets. Care must be taken for cold weather formulation by mixing proper amounts of calcium chloride and calcium bromide to maintain the solution above its freezing point during cool weather.
High-pressure drilling, workovers, and completion operations occasionally necessitate using densities to 19.2 lb/gal. Adding calcium chloride and calcium bromide to a zinc bromide solution can achieve a density of 19.2 lb/gal. Various concentrations of the three salts, in addition to other special products, can be used to formulate summer and winter blends.
Charts and tables for brine-water formulation are given in the Appendix. Example 8.1 shows a sample calculation for preparing CaCI2 brine. Metric
ION DIAMETER, A° Hydration Energy not hydrated hydrated* kcal/mot
*There is some variation in the figures for hydrated ion diameters found in the literature.
Fig. 8-7 Potassium ion sizing minimizes clay hydration (Courtesy NL Baroid)
material requirements for preparing CaCl, are given in the Appendix. Table B5 gives the composition of 1 bbl of sodium chloride/calcium chloride mixed brine.
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