BAKER HUGHES - Drilling Fluids Reference Manual

BOREHOLE PROBLEMS
S = pressure existing between pipe and wall cake in psi. During sticking process, this pressure
will range from 0 initially to that differential pressure which exists between the hydrostatic of the
fluid column and the formation.
f = coefficient of friction between the pipe and wall cake (laboratory data indicates coefficient of
friction values ranging from approximately 0.07 for invert emulsions to approximately 0.40 for
low solids, native fluids).
The above equation indicates that the sticking force may be reduced by altering the following
physical properties of a drilling fluid.
• Control fluid densities at lowest practical level consistent with control of formation pressure
and borehole stability.
• Monitor filtration and wall cake properties with emphasis on a thin wall cake. Evaluate effect
of time and temperature on the wall cake. The filter cake thickness of two fluids may be equal
in an API filtrate test (100 psi for 30 minutes), whereas the cake thickness could vary greatly
with an increase in time, pressure, or temperature. Static conditions produce filter cakes of
greater thickness as compared to dynamic conditions where the filter cake continues to erode
due to fluid flow.
• Control drilled solids at the lowest practical level.
• Utilize additives which aid in reducing friction coefficient and sticking coefficient.
• Severe conditions may dictate the use of an oil/synthetic fluid system such as CARBO-
DRILL ® /SYN-TEQ ® . This type of fluid offers maximum protection against wall sticking.
Other preventive measures against differential sticking are, (1) reduce area of contact between
collars and wall cake with spiral collars and/or stabilizers, and (2) minimize interruption of
pumping, particularly when the drillstring is not in motion.
Most instances of differentially stuck pipe are preceded by increases in torque and drag. Many
lubricants have been developed to minimize torque and drag, which in turn should reduce the
chances of differential sticking. Some of these lubricants are shown in Table 7-6 and will be
discussed in more detail under the section titled, Lubricity.
Product
LUBRI-FILM ®
MIL-LUBE TM
AQUA-MAGIC ®
Initial
Recommended
Treatments
4 lb m /bbl
0.5% to 2.0%
1.0% to 8.0%
Maintenance
Dependent upon fluid dilution
Dependent upon fluid dilution
Dependent upon fluid dilution
Table 7 - 7 Lubricants
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 7-35