BAKER HUGHES - Drilling Fluids Reference Manual

Hydraulics
Drill-In Fluids
Function
A drill-in fluid must possess the desirable properties of a good drilling fluid, as discussed earlier, and
provide the necessary attributes of a completion fluid. The primary function of a drill-in fluid is to
develop a filter cake which effectively prevents formation damage (production impairment) and which
is easily removed. As a standard, a drill-in fluid, like the drilling fluid itself, must provide lubricity,
inhibition, solids suspension, and well bore stability.
Development
Formation protection is critical while drilling the production zone since damage to the formation can
adversely affect the well’s production potential. This pay zone damage is minimized with the use of
drill-in fluids - specialized fluids for “drilling in” and protecting oil/gas producing formations.
Damage to the pay zone, including fine solids migration into the formation permeability channels,
clay swelling within the formation pore spaces, and irreversible reactions with invading polymers,
reduce the average permeability of the formation, resulting in lower production rates. Most formation
damage caused by conventional drilling fluids is by fluid invasion containing barite, finely ground
drill solids, and/or bentonite. Drill-in fluids have reduced the use of such non-acid soluble products
across the pay zone.
Attributes
A non-damaging drill-in fluid should ideally possess the following characteristics:
Easily removable filter cake
Acid soluble bridging agents
Bridging agents sized for flow-back through the designed completion process
Exhibit excellent fluid loss control
Temperature stability
Excellent lubricity
Provide inhibition
The reservoir drill-in fluid is designed to protect the pay zone during well bore construction, simplify
the clean-up process, and maximize production rates.
Screening and Selection
Selecting a reservoir drill-in fluid for a specific application to satisfy each of the above criteria must
involve laboratory testing of the candidate fluids using the following screening parameters.
Leak-off control tests
Net breakout pressure determination
Return permeability tests
Fluid-fluid interactions
Drill-in fluid properties
Environmental considerations
Reference Manual
Baker Hughes Drilling Fluids
1-34 Revised 2006