STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Bits and Downhole Tools 779
Tooth Wear. Tooth wear is estimated in eighths (4) of the initial tooth height.
Since tooth wear is likely not uniform on any row of teeth of a given cone, it is
advisable to take several readings and report an average figure. The following
is the terminology used to report tooth wear:
Tooth
Dullness Milled Tooth Insert Bits
T1
T2
T3
T4
T5
T6
T7
T8
Tooth height gone
Tooth height 4 gone
Tooth height 2 gone
Tooth height 3 gone
Tooth height 3 gone
Tooth height f gone
Tooth height g gone
Tooth height all gone
of inserts lost or broken
4 of inserts lost or broken
$ of inserts lost or broken
3 of inserts lost or broken
of inserts lost or broken
a of inserts lost or broken
g of inserts lost or broken
All of inserts lost or broken
Bearing Condition. The measurement of the bearing wear is very subjective. It
is recommended to estimate it in eighths of the life of the bearing.
Since mechanical aids are not available, it is necessary to eyeball the bearing
wear and estimate rotating hours left. Knowing the rotating hours of the bit at
the bottom of the well, it is possible to calculate the ratio. An estimation of
the total bearing life is expressed by a ratio of eighths of the bearing life
as follows:
Bearing
Condition
B1
82
B3
84
B5
B6
B7
88
Bearing life used:
Bearing life used:
Bearing life used:
Bearing life used:
Bearing life used:
Bearing life used:
Bearing life used:
Bearing life all gone:
-
4 (tight)
- 3
$ (medium)
- 5
3 (loose)
-
7
8
(Locked or lost)
Example
A roller rock bit is pulled out of the hole after 12 hr of rotation at the bottom.
The driller estimates that the worst cone could rotate 4 hr more before being
completely worn out; thus total bearing life estimated is 16 hr.
12 3 6 .
Therefore: - = - = -, 1.e. B6 is reported.
16 4 8