Page 442 - Practical Well Planning and Drilling Manual

Section 3 revised 11/00/bc 1/17/01 12:00 PM Page 418

[ ] Practical Wellsite Operations
3.6.6

Refer to the topics in Section 3.6.1 for more information on using
dull bit evaluations for future bit selection. Table 3-5 provides infor-
mation on dull bit features.

Table 3-4 Reason Pulled Codes
BHA Change bottom hole assembly DP Drill plug
DMF Downhole motor failure FM Formation change
DTF Downhole tool failure HP Hole problems
DSF Drillstring failure HR Hours on bit
DST Drill stem test PP Pump pressure (suspected washout)
LOG POH to run logs PR Penetration rate (based on CPF)
LIH Left in hole TD Total depth or casing point depth
RIG Rig repair TQ Torque (excessive or fluctuating torque)
CM Condition mud TW Twistoff
CP Core point WC Weather conditions

Table 3-5 Dull Bit Features

Dull Feature Possible Cause Possible Remedy

Broken teeth Junk Fish junk or drill with a mill
Excessive string vibra- tooth bit
tion or shock loading Avoid critical RPM, run shock sub
Excessive WOB Reduce WOB

Broken outer Running into ledges Run in carefully
teeth Excessive RPM Reduce RPM

Bit balling Bad hydraulics Review hydraulics
Mud properties Review mud properties

Cone dragged Bearing failure Reduce parameters or time in
Junk jamming cones hole; review bit choice
Avoid junk in hole

418