Clear Brine Fluids SolidsFree Brine Fluid Systems
These fluids are made from fresh water or are solutions made with water and the addition of one or more electrolytes. These fluids do not contain either suspended particles or viscosifiers, which means neither filtration control nor viscosity control are provided. Some brines are corrosive and when corrosion inhibitors are required, compatibility studies should be performed. Some brines are toxic and precautions should be taken to prevent contact with unprotected skin. Brine solutions can be prepared to give good inhibition of clays or shales in producing formations. In addition, common contaminants do not affect the brines.
Fluid densities can be prepared from fresh water (8.33 lb/gal) to saturated calcium chloride solution at 11.7 lb/gal. Higher densities may be achieved by the use of other electrolytes, but they may cause corrosion problems. The main salt solutions are calcium chloride, potassium chloride, mixtures of calcium chloride and calcium bromide, and mixtures of zinc bromide, calcium bromide and calcium chloride. Sodium bromide and sodium chloride are used in special circumstances where required densities are low and contamination is a problem. The most commonly-used brines are sodium chloride, and calcium chloride.
|
Table 1 "N Commercially Available Salt Solutions and Their Density Ranges | |
|
Density Range (lb/gal) |
Salt Solutions |
|
8.3 - 9.7 |
Potassium Chloride |
|
8.3 - 9.9+ |
Sodium Chloride |
|
10.1 - 11.1 |
Sodium Chloride/Calcium Chloride |
|
8.3 - 11.7 |
Calcium Chloride |
|
12.0 - 16.0 |
Zinc Chloride/Calcium Chloride |
|
9.8 - 10.9 |
Potassium Bromide/Potassium Chloride |
|
10.0 - 12.4 |
Sodium Bromide/Sodium Chloride |
|
11.7 - 15.1 |
Calcium Bromide/Calcium Chloride |
|
\J5.0 - 19.2 |
Zinc Bromide/Calcium Bromide/Calcium Chloride J |
Sodium Chloride - Sodium chloride brines have been used extensively for a number of years as completion fluids. The brines are readily available in most active producing areas with densities up to 10 lb/gal. In areas where brine solutions are not readily available, they can be prepared by adding common salt to fresh water.
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f Table 2 Requirements for Preparing Sodium Chloride Salt Solutions (60°F) (Final Barrel Based on 100% Material Purity) | ||
|
Density (lb/gal) |
Fresh Water (gal/final bbl) |
Sodium Chloride (lb/final bbl) |
|
8.33 |
42.0 |
0 |
|
8.6 |
41.2 |
16 |
|
8.8 |
40.5 |
28 |
|
9.0 |
40.0 |
41 |
|
9.2 |
39.5 |
54 |
|
9.4 |
39.0 |
68 |
|
9.6 |
38.5 |
82 |
|
9.8 |
38.0 |
95 |
|
10.0 |
37.5 |
110 |
Salt solutions were formerly considered too corrosive to be used as workover or completion fluids or as packer fluids. The corrosion problem can be solved by adjusting the pH of the solution to above 10.5; however, pH measurements may be less important than measuring and controlling the p-alkalinity of the filtrate; this value should be kept above 1 cc. Lime or caustic soda may be used for pH control.
Adjustment of pH, or alkalinity, does not necessarily ensure the solution to be corrosion resistant. It may be necessary to use a corrosion inhibitor to achieve lower corrosion rates. In some cases, an oxygen scavenger might be used in conjunction with a filming amine inhibitor.
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