The concept that oil is a better drilling fluid than
water for well completion has been prevalent for a long time in the oil
industry. Water Based Muds damage producing zones, whereas, oil has
less effect on clays and water soluble materials in the formation.
This has led to the use of crude oil when drilling into the production
zone. However, certain disadvantages of crude oil became obvious:
-
There was no control of rheology or gel strength to obtain
good cuttings, lifting and suspension.
-
There was no control of spillage or filtration into the permeable
zones, which resulted in loss of drilling fluid and possible formation
damage.
-
Water became incorporated in the oil and was free to wet
the cuttings and enter the formation.
If an oil mud containing 0% water could be prepared and maintained,
it would be distinctly different from other drilling fluids. The
reason for this is that corrosion couldn't occur in such a mud and this
is what makes oil based muds so desirable. Some the most desirable
features of oil based muds are as follows:
-
Completely flexible in properties throughout the weight range,
viscosity range and all practical ranges of temperatures while drilling.
-
Nearly perfect plastering properties.
-
Nearly perfect deplastering properties are possible which
will allow the return of permeability from the producing formation.
-
Won't lose any water to the producing formation.
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