BAKER HUGHES - Drilling Fluids Reference Manual

RESERVOIR APPLICATION FLUIDS
wall, the formation face, and transfer pipes. The rheological properties of the fluid to be displaced
can then be adjusted to make it flow more easily when the actual displacement takes place.
During the drill-in phase, wellbore sections become exposed to mud and mud particles. Drilled
solids become attached to the casing and become a part of the filter cake in the open wellbore.
Regardless of the type of completion, these foreign particles, if not removed from the wellbore,
may damage the reservoir and the completion assembly. Some completion methods will require a
more thorough cleansing process than others.
The procedures described below are generalized recommendations.
Displacement Objectives
The basic displacement objective is the same regardless of the completion type or procedure. For
example, if a drilling fluid is being displaced to drill-in fluid, contamination of the drill-in fluid may
occur and spacers must be incorporated to avoid intermingling. Likewise, when a drilling fluid or
drill-in fluid is displaced to clear brine, the solids-free brine will become contaminated and similar
safeguards are required.
A successful displacement should accomplish the following:
• Remove mud and unwanted debris from the open-hole, casing and riser (if applicable).
• Maintain the integrity of the mud and completion fluid interface.
• Minimize rig time.
• Minimize brine filtration and expense.
• Minimize waste and disposal costs.
• Minimize the need for stimulation and promote a clean, undamaged and productive wellbore.
Pre-Displacement Considerations
A. Cleaning the Wellbore
B. Indirect versus Direct Displacement
C. Forward versus Reverse Circulation
D. Clean-out String Bottom Hole Assembly
E. Conditioning the Mud System
F. Surface Pits and Equipment Cleanup
G. Design of Displacement Pills
Cleaning the Wellbore
It is always desirable to have a clean wellbore. Historically, some problems have been encountered,
especially during the completion phase, due to insufficient displacement and well clean up.
• Junk and solids can both prevent future well intervention activity or interfere with the running
of perforating guns
• Solids and junk both result in the inability to run the completion process, typically by early
setting of packers
• Solids and gunk have both caused problems functioning CIV/FIV type valves requiring bailer
runs or coiled tubing intervention
• Gunk offers a serious risk to formation damage if serious losses occur
• Debris on top of wire line plugs can prevent their recovery
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 6-81