BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
API Filtrate Reduction – If reductions in API filtrate are required, additions of MIL-PAC should
be used. Concentrations required will vary depending on the degree of reduction needed.
Seawater/KCl Systems
Depending upon how massive the sections of salt are, there may be little or no effect on the
system except for an increase in chloride concentration. If reductions in rheological properties or
API filtrate are required, the same methods of treatment as above should be used except for
dilution.
Saturated-Salt Systems
If the formations being drilled are massive enough to require saturation of the fluid, several
differences should be noted. Viscosity reductions will occur from (1) the effect of salt saturation
on the NEW-DRILL, and (2) the shrinkage of the water envelope around the clay solids.
Additions of a viscosifier such as XAN-PLEX may be required to maintain hole cleaning
properties. The API filtrate will need to be controlled with either MIL-PAC, PERMA-LOSE,
BIO-LOSE, MILSTARCH, or a combination of these polymers. Typically, a combination of
MIL-PAC to MILSTARCH (in a 1 to 4 ratio) often gives the most economically acceptable filter
cake.
Effects on Fluid Properties
In a freshwater drilling fluid, an increase in the salinity of the fluid will cause the clay solids to
flocculate. The result of this flocculation is an increase in yield point, gel strengths, and API
filtrate. The pH of the fluid will also be reduced slightly.
The NEW-DRILL polymer itself is not adversely affected by increasing salt concentrations;
however, the normal viscosity obtained from the polymer is reduced as the chloride content
increases NEW-DRILL systems have been used effectively to inhibit shales in salt-saturated
environments. If the NEW-DRILL system is made up from a brine such as KCl or NaCl, the
effects from salt “contamination” will be much less severe or, in most cases, negligible.
Salt Water Flows
The effects of salt water flows on a NEW-DRILL system will be similar to that of drilling salt
except for (1) reductions in fluid density of heavily weighted fluids, and (2) increases in the
concentration of soluble cations and anions. Almost all water flows contain cations in addition to
sodium, usually calcium and magnesium. Total hardness levels should be maintained below 500
mg/L by maintaining the pH from 9.0 to 9.5 and using soda ash to remove residual calcium not
removed by adjusting the pH.
Note:
A note of caution regarding NEW-DRILL, at elevated pH. The product will hydrolyze and
thus loose its clay inhibitive qualities. If hardness is present and pH is elevated to the high
pH range the calcium cation will precipitate and in so doing precipitate out the NEW-
DRILL polymer with it.
Reference Manual
Baker Hughes Drilling Fluids
3-56 Revised 2006