BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
Complex Systems
NEW-DRILL ® System
The term “low-solids/polymer” fluids include variations from a simple formulation for shallow
drilling to much more complex formulations for a wide variety of drilling objectives. The
“polymer fluid” of the 1990s ranges from fresh to saturated salt water, from zero clay content to
over 20 lbm/bbl (0% to 8% by volume low-gravity solids), with pH values from near neutral (7.0)
to as high as 11.0. This family of fluids has one primary “thing” in common. These fluids all
achieve their performance characteristics from the presence of a protective colloid (water soluble
organic polymer) or a combination of both protective colloids and salts.
The performance of partially hydrolyzed polyacrylamide (PHPA) polymers such as NEW-DRILL
is significant in encapsulating cuttings and improving solids removal efficiency. By bonding on
sites that would otherwise react with water, these polymers “inhibit” the dispersion (physiochemical
breakdown) of cuttings and formation solids into the fluid system. Due to their high
molecular weight, these molecules are infinitely longer than they are wide or thick. At small
concentrations (0.25 to 3.0 lbm/bbl) they impart a high level of cuttings encapsulation to waterbase
fluids (even in freshwater).
The philosophy of engineering the NEW-DRILL ® system is geared towards maintaining the low–
gravity solids content of the mud at or below a level of 5% by volume. This solids control level
will insure a high-quality filter cake. Higher solids content result in a thick cake conducive to
differential sticking.
Another objective, accomplished by the low content of drilled solids in these fluids, is a low
impediment to fluid flow. Lower friction means lower system pressure losses as compared to a
fluid with higher solids content. This converts to less pump wear, lower diesel consumption, and
better opportunity for hydraulic horsepower to do work at the bit. Lower viscosities at high rates
of shear convert to better separation (within pieces of solids removal equipment) of drilled solids
from whole fluid. This enhances the performance of all the screens, hydroclones, and centrifuges.
Even lower total solids content is possible when using iron oxide or ORIMATITA as a weighting
agent. Since its specific gravity is 5.0 to 5.1, fewer solids will be present (in the ratio of 4.2 to
5.0) at a given fluid density when compared to a barite weighted fluid.
Materials used to control various fluid characteristics differ greatly. Although the NEW-DRILL
family is not normally thought of as a potassium-base fluid, many NEW-DRILL fluids have used
KCl or other K + sources as an additional inhibitor. (Confusion abounds as to whether a name
really describes a drilling fluid.)
A key point to note is that in some shale compositions and various areas around the world, NEW-
DRILL alone has been effective in achieving good caliper logs. In some areas, it appears that as
little as 1% KCl, 3% KCl, or up to 6% KCl has been effective where NEW-DRILL alone has not.
Commonly the combination of NEW-DRILL and potassium has yielded a synergistic effect
which outperforms either additive when independently applied.
Many laboratory tests and field case histories have shown increased clay swelling/hydration
inhibition with the addition of a partially hydrolyzed polyacrylamide (PHPA) to a KCl or NaCl
type fluid. NEW-DRILL ® HP is especially effective, being able to be stored and mixed more
effectively due to being blended with KCl. These reasons explain why NEW-DRILL HP is often
more cost effective than competitive products claiming to have “higher activity” or being “pure”
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 3-51