BAKER HUGHES - Drilling Fluids Reference Manual

Hydraulics
Completion Fluids
Definition
By definition, workover or completion fluids are fluids placed across the producing zones before or
immediately after perforating, or any fluid placed across the formation during reworking, underreaming,
drill-in, or gravel pack operations. These fluids help ensure that production is consistent
with the expected potential of the well.
Function
The primary functions of completion/workover fluids are to:
provide pressure control by preventing formation fluids from entering the borehole
maintain borehole stability
minimize formation damage
control fluid loss with minimal solids invasion
These fluids also keep the borehole “clean” of perforation debris, solids such as drill cuttings, sand,
etc., or any other contaminants by providing a transportation medium that for circulating loose
material to the surface.
Attributes
A completion/workover fluid must possess the following attributes:
• enough density to control subsurface pressures
• enable efficient solids removal during circulation through filtration systems
• stable, nontoxic, low corrosivity, and bacterial growth retardant
• non-reactive to other soluble salts, minerals, cement, etc.
• retain desirable properties such as viscosity and other physical properties under prolonged
exposure to high shear
• readily degas
Mechanisms for Formation Damage
For a well to be profitable, the reduction of virgin permeability should be minimized. Permeability
can be reduced by the invasion of foreign liquids and/or solids into the near well bore region. This
hampered permeability or damaged zone is known as a skin effect.
A critical function of completion fluids is to contain formation pressures. To accomplish this,
hydrostatic pressure must be higher or equal to the pressure of the formation. Consequently, if the
hydrostatic pressure is higher, the fluid would allow a certain amount of solids and liquids to be lost to
the formation.
Reference Manual
Baker Hughes Drilling Fluids
1-44 Revised 2006