BAKER HUGHES - Drilling Fluids Reference Manual

Baker Hughes Drilling Fluids
12. High Penetration Rate
The use of lower solids content oil-base drilling fluids, combined with the advent of polycrystalline
diamond cutter (PDC) bits, has resulted in the ability to drill with high penetration rates throughout the
world. The modification of drilling fluid properties and bit design allows for increased penetration
rates in all type of shales, from soft gumbo to the older hard shales.
13. Flexibility
With the advent of both “relaxed” oil-base fluids and low toxicity oil-base fluids, any size hole, any
environment, and any lithology, can be drilled with a specially tailored oil-base fluid.
14. Reduction of Stress Fatigue
Stress fatigue of tubulars is reduced considerably when using oil-base fluids, i.e. less tubular torque
and corrosive attack from formation acid gases.
15. Reduced Corrosion
Oil fluids are not corrosive since oil, instead of water, is in contact with all tubulars.
Disadvantages of Oil-Base Fluids
1. High Initial Cost per Barrel
Initial make-up costs can be high. A barrel of oil-base fluid has a high initial cost and maintenance
costs can climb substantially depending on the environments encountered. These costs fluctuate with
the price of the oil.
2. Mechanical Shear Required
To achieve the emulsion stability and viscosity required, mechanical shearing is necessary to form a
tight emulsion and disperse the organophilic platelets. This can be accomplished by using a highpressure
pump in conjunction with special shearing devices or shearing through the drill bit.
3. Reduced Kick Detection Ability
H 2 S, CO 2 , and hydrocarbon gases such as methane (CH 4 ) are all soluble in oil-base fluids. If gas
enters the wellbore, it can go into solution under pressure and as the gas moves up the hole it can
break out of solution and expand at a very rapid rate, thus emptying the surface well-bore and reducing
the hydrostatic pressure allowing additional kicks to be taken. If this occurs at a shallow depth, it may
be too late to prevent a blowout. All kicks in oil-base fluids must be treated as a gas kick and
circulated through the choke.
4. Pollution Control Required
Most areas where oil-base fluid is used have environmental restrictions. Rig modifications may be
necessary to contain possible spills, collect or clean cuttings, and handle whole fluid without dumping.
Environmentally acceptable disposal procedures must be followed when discarding cuttings and whole
mud.
5. High Cost of Lost Circulation
Lost circulation with is very expensive due to the mud’s cost per barrel. The problem may not be
curable. Therefore, it may not be practical to use of oil-base fluids where lost circulation is anticipated.
Seepage losses are a common occurrence with oil-base fluids. Formations with low permeability and
porosity may exhibit no losses when drilled with a water-base fluid, however, a partial or full loss of
Baker Hughes Drilling Fluids
Reference Manual
Revised 2006 5-3