BAKER HUGHES - Drilling Fluids Reference Manual

BOREHOLE PROBLEMS
• Use of fluid additives such as MIL-LUBE ® , BIO-DRILL ® , PENETREX ® , or the
environmentally friendly TEQ-LUBE ® or LUBE 622 minimizes the build-up of clay solids on
the drillstring and bit.
• Controlled penetration rates may be necessary in troublesome zones.
• Improved hydraulics may alleviate bit balling in some cases.
• Inhibitive fluids such as CARBO-DRILL ® , SYN-TEQ ® , ALPLEX ® , PERFORMAX
and potassium-base and/or calcium-base drilling fluids (lime and gypsum fluids) may provide
sufficient protection against swelling and sticky shale. Plastic deformation (flow of shales into
wellbore) may be controlled or minimized with these systems. In most cases, however, it is
necessary to increase drilling fluid density to restrain plastic flow of shales.
• Wellbore deviation also must be considered as a factor in wellbore constriction. In deviated
wellbores of 30 degrees and higher the cuttings bed forms on the low side of the annulus and
with improper hole cleaning the cuttings bed will build, reducing the annular opening. These
beds travel up the wellbore in dune-type movements. That is, as the bed reaches a given height
of deposition it will be washed higher up the wellbore to be deposited until a deposition height
reaches a sufficient height to be washed again. This movement of the cuttings bed causes
pressure fluctuations within the annulus, due to varying wellbore diameter restrictions. These
cuttings beds are unstable and tend to “avalanche” (slide back down the hole). These
avalanches can, in the worst case, cause packing-off of the annulus. It is recommended to run
hole cleaning simulations in ADVANTAGE in order to identify, and if possible remedy, the
formation of cuttings beds.
Another possible cause of annular restriction is wall cake build-up. This problem is normally
associated with low annular velocities, high filtrate values, and permeable formations. It can
generally be alleviated by reducing the API Filtrate (thinner wall cake) and/or the differential
between fluid hydrostatic and formation pressures.
Seepage Loss
Seepage loss (