Page 443 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 419

3.6.6
Drill Bits [ ]

Table 3-5 Dull Bit Features (cont’d)

Dull Feature Possible Cause Possible Remedy

Cone interference Drilling on junk Avoid junk in hole
Mechanical damage RIH carefully past ledges
hitting a ledge
Pinched bit from running Ream in undergauge hole
into undergauge hole

Chipped teeth Junk in hole Avoid junk in hole
or cutters Hard nodules within Use high flow rates and
formation reduced WOB and RPM
Shock loading Avoid critical vibrations, run
a shock sub

Erosion Excessive bit hydraulic Use larger nozzles if erosion
horsepower per square likely to lead to premature
inch (HSI) failure (lost cutters)

Heat checking Balling See “Bit balling” above
Low flow rate Increase flow rate (may
need larger nozzles)

Lost cone Too long in hole Use CPF calcs
Inadequate supervision Listen to the hole
Junk in hole Avoid junk
Bit faulty Send back bit and any junk
fished to manufacturer

Pinched bit Run into undergauge hole Ream in undergauge hole

Round gauge Abrasive formation Use enhanced gauge
protection bit

Ring out (PDC or Junk Avoid junk in hole, run a junk
diamond) Wrong bit choice sub on previous bit run when
PDC or diamond bit anticipated
Excessive WOB
Review bit choice
Reduce WOB

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