Page 220 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 196

[ ] Well Programming
2.4.6

Table 2-1 Bit Features
Condition Helpful Bit Features Detrimental Bit Features

Abrasive sands and Diamond-enhanced gauge PDC bits are generally
mobile or very permeable protection and roller not suitable.
zones leading to under- reamers.
gauge hole (reaming in).

Highly plastic shales. Mill tooth cutters. Tungsten carbide inserts
sometimes do not per-
form well in very plastic
formations.
High-compressive TCI bits and sealed jour- Mill tooth bits will wear
strength. nal bearings. quickly and PDC bits are
generally limited to appli-
cations below about
20,000 psi. Security is
researching PDC designs
for formations up to
50,000 psi.

Very high-compressive Natural diamond bits.
strength.

Reactive shales in water- Bit balling may be expect-
based mud. ed; center jets on tricone
bits. Large flowby areas
on PDC bits (bladed
designs).

Motor applications. High-speed sealed roller Journal bearings tend to
bearings and fixed cutter overheat at very high
bits. rotary speeds.
Deep, hot, high pressure. Metal to metal sealed Elastomer seals are more
bearings or fixed cutter likely to fail early in
bits. harsh conditions.

Directional wells with Bits with side-cutting Parabolic fixed cutter bits
high build rates. action and small gauge and/or bits with long
lengths. gauge areas.

Hard nodules in forma- Mill tooth bits are gener- PDC cutters may shatter
tion (cherts). ally best, but TCI may be when hard nodules hit.
applicable.

196