BAKER HUGHES - Drilling Fluids Reference Manual

Hydraulics
Table 1-5
Typical pH Levels of Some Common Drilling Fluid Additives
Material
PH
CHEMTROL ®
9.0
LIGCO ®
4.5
LIGCON ®
9.5
NEW-DRILL ®
8.7
UNI-CAL ®
4.5
SAPP
4.8
Sodium Bicarbonate (NaHCO 3 )
8.3
Sodium Carbonate (Na 2 CO 3 ): soda ash
11.0
Sodium Hydroxide (NaOH): caustic soda
13.0
Calcium Hydroxide (CaOH 2 ): lime
12.0
Calcium sulfate dihydrate (CaSO 4 H 2 O): gypsum
6.0
Potassium Hydroxide (KOH): caustic potash
12.8
MIL-BAR ®
7.0
MILGEL ® 8.0
The alkalinity of a solution is related to pH since alkalinity is the measure of the quantity of an acid
needed to reduce the pH of a filtrate to a particular value. The two common filtrate alkalinities
utilized in fluid analysis are P f and M f . P f alkalinity is the volume of N/50 (0.02 normal solution)
sulfuric acid required to reduce the pH of 1 cc of filtrate to 8.3. The end point is noted when the
phenolphthalein indicator solutions changes from pink to colorless.
M f is the quantity of N/50 sulfuric acid required to reduce the pH of 1.0 cc of filtrate to 4.3. The end
point is obtained when a methyl orange indicator solution changes from orange to salmon pink or red.
If the sample color is obscured with organic materials, the pH can be determined with a glass
electrode pH meter.
If there were no interfering ions present, the P f and M f alkalinities could be used to calculate the
amounts of OH¯, CO = 3 , and HCO 3¯ ions present in the filtrate. However, the presence of organic acids
or buffering ions cause the M f determination to indicate more CO = 3 and HCO 3¯ ions than actually
present. This is the usual case in fluid filtrate, and the M f determination is only a very rough indicator
of the CO = 3 and HCO 3¯ions present. As a general guide, M f values above 5 mL indicate that excessive
amounts of CO = 3 and HCO 3¯ ions are probably present in the fluid.
When excessive concentrations of CO = 3 and HCO 3¯ are suspected, another titration procedure, as
shown in the Measurement of Carbonates (p 2-87 Water-Base Fluid Systems) in the Fluid Facts
Engineering Handbook, can be used to determine their concentrations.
Another alkalinity measurement (Pm) is made with the whole fluid rather than filtrate. This test (refer
to Fluid Facts Engineering Handbook for details) is made in a manner similar to the P f test and is used
primarily to determine concentrations of lime and cement being carried as solids in the system.
Because it has limited solubility, considerable cement may be carried as a solid which tends to
replenish calcium and hydroxylions as they are used up. This can be a problem when it is necessary
to calculate the quantity of treating agent to neutralize the cement.
Reference Manual
Baker Hughes Drilling Fluids
1-32 Revised 2006