BAKER HUGHES - Drilling Fluids Reference Manual

RESERVOIR APPLICATION FLUIDS
Improved direct displacement techniques (specialized spacers) and increased daily rig costs have
reduced the use of indirect displacements.
The indirect displacement involves the use of forward or reverse circulation. The complete
displacement process includes two phases; (1) displacement of the drilling fluid in the wellbore to
seawater or drill water and (2) displacing the seawater to the next drilling fluid or brine.
Deviated wellbores represent unique hole cleaning challenges. As wellbore inclination increases,
axial particle slip shifts to radial particle slip, causing the cuttings to fall to the low side of the
borehole, thus increasing the transport difficulty.
As hole angles approach horizontal inclinations, displacements in deviated wells utilize
increasingly greater spacer volumes and high annular velocities to move mud debris out of the
wellbore. Some operators are more willing to displace the casing to seawater or drill water (an
indirect displacement) because the larger water volumes are inexpensive and longer pump times are
possible. The second phase, displacement to the drilling fluid or brine, is intended to clean and
water-wet the casing and requires less pump time.
Water-Base System (WBM) to Brine
General Procedure
Pre-Displacement
Run the workstring to bottom and condition the mud.
Displace the WBM to Water
Pump a viscous push pill containing Xanthan Gum spaced between the mud and seawater. The
spacer viscosity should be ~150-300 sec/qt and formulated by adding 3 lb Xanthan Gum per bbl
seawater. The volume of the viscous push pill should cover approximately 1000 feet of annulus.
Follow the pill with seawater and circulate and filter to the operator-specified limit.
Displace Seawater to Brine
Pump viscosified seawater containing CASING WASH TM 100. Circulate at least one hole volume.
Follow with a viscous Seawater/ Xanthan Gum spacer between brine and seawater. The viscous
spacer should cover 500 to 2000 feet of widest annular diameter.
Follow with filtered brine until operator’s turbidity requirements are achieved.
Oil-Base/Synthetic-Base System to Brine
General Procedure
Invert emulsion systems having highly aromatic oils will contain hydrocarbons in the slop water.
Proper containment will be necessary to avoid unlawful discharge of these fluids. Additionally, all
spacers should be disposed of as per regulations, or the operator’s specific requirements. See
attached additional information on proposed treatment of oil-contaminated water and brine.
Pre-Displacement
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 6-85