21. Method of Diluting Raw Acid.

the raw acid in terms of Baumé (°Bé) or the Specific Gravity (s.g.). The first step in
the mixing acid is to measure the density as follows:
1. Put a sample of the raw acid to be tested in a 250 cc cylinder and take
the degrees Baumé (or specific gravity) reading with a hydrometer.
Also take the temperature of the sample.
2. Correct the degrees Baumé or specific gravity to the standard
temperature of 60° F (16° C) by using the correction factors listed in
Table .
3. Convert the corrected degrees Baumé or specific gravity to percentage
of HCl using Figure 29, page 148.
4. Use dilution charts (see Mixing Manual or Engineering Handbook) to
determine how much raw acid is required to mix 1000 gallons (litres) of
acid at the desired strength. Alternatively the following equation can be
used.
Gallons of Strong Acid = 1000 x (s.g. Weak Acid) x (% Strength Weak Acid)
Per 1000 gallons Weak (s.g. Strong Acid) x (% Strength Strong Acid)
Litres of Strong Acid = 1000 x (s.g. Weak Acid) x (% Strength Weak Acid)
Per 1000 Litres Weak (s.g. Strong Acid) x (% Strength Strong Acid)
Where °Bé = 145 - 145 or s.g. = 145
s.g. 145-°Bé
To use Table to correct the degrees Baumé (Bé) or specific gravity to the standard
temperature of 60° F (15° C), choose the °Bé or specific gravity reading closest to
that of the reading measured with the hydrometer.
· If the acid temperature is above 60° F (15° C), add the correction value
shown for every 1.0° F above 60 °F.
· If the acid temperature is below 60° F (15° C), subtract the correction
value shown for every 1.0° F below 60 °F.

Example.
Acid sample Hydrometer reading = 20.4 ° Bé
Acid Sample Temperature = 45 ° F
Correction Factor for 20 Bé = 0.04 per 1.0 °F
Temperature Difference from 60° F = 60 - 45
= 15 ° F
Temperature correction = 0.04 x 15
= 0.8 ° Bé
Temperature is below 60° F (subtract) = 20.4 - 0.8
Corrected °Bé at 60° F = 19.6 ° Bé
Acid Strength = 30.6 %
(From Figure 29, page 148)
Specific Gravity = 145
(145-19.6)
= 1.156 s.g.
Required Acid Strength = 15 % HCl
Specific Gravity = 1.075
(From Figure 29, page 148)
Raw acid required to mix = 1000 x 0.15 x 1.075
1000 gallons of 15% acid 0.306 x 1.156
= 161.25
0.3537
Gallons of Raw acid required = 455.9 gallons
(at 19.6° Bé)
Gallons of water required = 1000 - 455.9
= 544.1 gallons
Note that when obtaining the volume of water required for proper dilution of the raw
acid, that additives such as corrosion inhibitors, NE-Additives etc. are considered
part of the dilution water requirement. Therefore, all additive volume must be
subtracted from the volume of dilution water.
Corrosion Inhibitor = 2.0 gallons CI-Additive
(2.0 gallons/1000 gallons)
NE-Additive (Non-emulsifier) 0.6% = 1000 x 0.006
= 6.0 gallons
Total Additives = 6.0 + 2.0
= 8.0 gallons
Water required = 544.1 - 8.0
= 536.1 gallons
Final Mixing Requirements = 536.1 gallons Water
for 1000 gallons = 2.0 gallons CI-Additive
= 6.0 gallons NE-Additive
= 455.9 gallons Raw Acid
If the volume of acid required for a job, or the mixing tank is greater or less than
1000 gallons a simple factor can be calculated to convert the required volumes. For
example if the required volume was 750 gallons:
Volume factor = 750 ÷ 1000
= 0.75
New Mixing requirements:
Water (0.75 x 536.1) = 402.1 gallons
CI-Additive (0.75 x 2.0) = 1.5 gallons
NE-Additive (0.75 x 6.0) = 4.5 gallons
Raw Acid (0.75 x 455.9) = 341.9 gallons
Total = 750.0 gallons

21.2 Loading and Mixing HCl Acid.

When preparing for an acid job, it must be ensured that the acid should be uniform
throughout the tank. The raw acid, dilution water, and all additives must be
thoroughly mixed together. The best loading method is as follows:
1. Load the volume of water (freshwater whenever possible) less the
volume of additives needed.
Note : Water should always be added first to prevent excessive heat
being evolved and causing an explosion that can occur when water is
added to raw acid.
2. Add the required concentration of inhibitor and NE-Additives
separately. Do not mix any inhibitor or NE-Additives together or
combine any NE-Additives in the same container. Chemical reactions
can occur, and emulsion tests for proper additives would become
useless. Always add each additive separately.
3. Add the volume of raw stock acid required to the volume of water and
additives already in the tank. Keep the end of acid loading hose above
the fluid level in the acid tank to aid in mixing the water, additives and
acid.
4. When the required volume of liquid is placed in the tank additional
mixing is necessary by one of the following methods:
· Circulate the acid with a pump
· Mix the acid with a paddle or auger (Where available).
· Mix the acid by bubbling air for 10 to 15 minutes. This should not
be used where other methods are available. Oxygen may
become dissolved in the acid and create problems of corrosion
in the well.
Agitation during transportation (where acid is premixed in transportation tanks)
cannot be relied upon for properly mixing the treating solution.

21.3 Loading and Mixing HCl:HF Acid.

In sandstone stimulation, HF is normally used in combination with HCl. Mixtures of
the two acids may be prepared by dilution mixtures of the concentrated acids with
water or more commonly by the addition of fluoride salts such as ammonium
bifluoride with water and then raw stock acid. The fluoride salts dissolved in water
release HF when mixed with HCl. Fresh water should always be used for mixing
HCl:HF acid, and no field waters containing sulphate, calcium, sodium or potassium
ion should be used.
HF is poisonous, alone or in mixtures with HCl it should be handled with extreme
caution. Mixing proportions of HCl:HF at various strengths using ammonium
bifluoride can be found in the Engineering Handbook or in the Mixing Manual. Table
to Table can also be used for this purpose.
Note: The concentration of HCl required for mixing is always higher than the final
concentration desired as part of the HCl is consumed in changing the ammonium
bifluoride to HF.
Mixing HCl:HF requires rapid agitation or circulation of the water to facilitate the
dissolving of the ammonium bifluoride, and proper mixing of all acid ingredients.
The following procedure should be used when preparing HCl:HF.
1. Place the required volume of dilution water in the acid tank.
2. With agitation, add the remaining ingredients in the following order to
allow complete mixing or dissolving of the additives: corrosion
inhibitors, NE-Additives and ammonium bifluoride.
3. With agitation, add the required amount of raw acid and agitate until
uniform.