BAKER HUGHES - Drilling Fluids Reference Manual

Water Based Drilling Fluids
The degree of torque is usually strongly influenced by the size of the cuttings bed upon which the
pipe string is rotating. Often, the more inclined the hole, generally the larger the cuttings bed.
This is increased by the amount of wall instability experienced (hole closure).
Effect on Differential Sticking
Differential pressure sticking is a condition in which the drill pipe becomes stuck against the wall
of the wellbore because it has become embedded in the filter cake. There must be a permeable
formation present and a pressure differential across a nearly impermeable filter cake. The quality
of the filter cake and the rate of filtrate produced by the drilling fluid in use affect the possibility
of differential sticking.
NEW-DRILL fluids exhibit a compressible filter cake which helps considerably in preventing
differential sticking. The NEW-DRILL system has accomplished this without the traditional
liberal use of commercial bentonite. Cases of differential sticking in the field while using a
NEW-DRILL system have been rare. In fact, highly depleted zones have been drilled utilizing
the NEW-DRILL system with no occurrence of differential sticking. This has helped reduce fluid
cost and prevent one of the most costly delays in drilling - stuck pipe
Effects on Weight-On-Bit (WOB)
Due to the reduced coefficient of friction from the NEW-DRILL, more effective collar weight is
transferred to the bit. Less collar-to-wellbore friction has multiple benefits including less drill
string wear. Reductions in torque of as much as 50% have been observed in the field.
NEW-DRILL Operational Procedures
NEW-DRILL systems have been developed through experience in several geographic areas under
various drilling conditions. Consequently, techniques have been developed to meet the needs of
customers at various locations.
Methylene Blue Test (MBT)
The performance of the NEW-DRILL System is based on a low colloid philosophy. Utilize
solids control equipment for controlling solids content and plastic viscosity. Daily solids analysis
must be used to monitor the solids content. Low gravity solid content is the key to proper control
of the system. Total low gravity solids should be held in the range of 3 to 5% by volume,
inclusive of commercial clay. Inadequate solids control equipment will cause increases in solids
content and result in high rheological values and/or the need for a strong deflocculant such as
UNI-CAL (lignosulfonate).
Gel Strengths
Gel strength values as determined by a 6-speed viscometer are generally higher for a NEW-
DRILL system than traditional UNI-CAL lignosulfonate fluids. This illustrates the difference
between a semi-dispersed as compared to a dispersed mud system. Also, the aqueous phase
viscosity of the lignosulfonate system is only slightly greater than water while the NEW-DRILL ®
system’s water is significantly thicker. It is common for 10-minute gels to reach 35 lb f /100 ft 2 .
Drilling conditions and economics should determine the need to reduce gel strengths. Report the
initial, 10-minute and 30-minute gel strengths on all NEW-DRILL systems.
Reference Manual
Baker Hughes Drilling Fluids
3-60 Revised 2006