BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
The pH of many water-base drilling fluid systems is maintained in the 9.5 to 10.5 range for
the following reasons:
• Organic dispersants and filtration control agents generally achieve maximum effectiveness in an
alkaline environment.
• Adverse effects of contaminating electrolytes are usually minimized at higher pH levels.
• Corrosion rates can be reduced at higher pH levels and bacterial action on organic materials is
retarded at elevated alkalinity levels.
• Thermal stability of lignosulfonate systems may be improved at a pH of 10.0 or above.
The pH ranges of some of the more common water-base fluid systems are shown in Table 1-4.
Table 1-4
Type System
UNI-CAL ® , Freshwater
UNI-CAL ® , Seawater
UNI-CAL ® , Gypsum
NEW-DRILL ®
Lime-Base
BENEX, Low-Solids
Saturated Saltwater
KCl Systems
Fluid System pH Ranges
pH Range
9.0 - 11.5
10.0 - 11.5
9.0 - 10.0
8.5 - 10.0
11.5+
9.0 - 10.0
9.5 - 11.5
10.0 - 11.5
Note:
Increasing concern with corrosion control has led to higher pH values. Usually, pH values
below 10.5 are compatible with most shales drilled, however, there are some shales which
exhibit poor stability in the presence of excess hydroxyl ions. UNI-CAL ® systems function
effectively over a broad pH range and have been run as low as 8.0 to 8.5 to improve shale
stability.
Approximate pH of some common fluid additives are listed in Table 1-5
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 1-31