BAKER HUGHES - Drilling Fluids Reference Manual

RESERVOIR APPLICATION FLUIDS
Filtered Brine
Push Pill
Drill-In Fluid
Casing Scrapers
Stabilizers
Figure 6 - 19
Reverse Circulation
Drill-In Fluid
Push Pill
Filtered Brine
Casing Scrapers
Stabilizers
Figure 6 - 20
Forward Circulation
However, there is a serious drawback to the reverse circulating technique. First, the drawback is
that the friction pressure from pumping the entire length of the workstring at a high rate is imposed
at the bottom of the wellbore, rather than at the surface. Secon, it also eliminates the possibility of
rotating the workstring during displacement due to the closed BOP.
Clean-out String Bottom Hole Assembly
The following equipment can be used to clean and remove debris from the inside of casing:
Casing scrapers should be used on the workstring in accordance with the casing schematic for
each casing. Each casing section should have a scraper/brush placed not more than 100 feet above
each casing shoe. These devices will help remove any solids that may adhere to the casing walls so
the displacement fluid can move them out of the hole. A casing scraper should create maximum
contact with internal diameter of casing, and be of a one-piece design with full drill pipe strength
with no weak internal connections. Casing scrapers should enable rotation at rates up to 50 rpm, but
conventional scrapers are not built for extended rotation or drilling, i.e. extensive rotation at the
same spot should be avoided. Rotation and reciprocation of the drill pipe is recommended during
displacement and clean up. Casing brushes are not considered necessary if an effective scraper is
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 6-89