STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

784 Drilling and Well Completions
Reaming considerations are:
1. Select a bit with minimum offset.
2. Select a bit with “L” or “T”-shaped gage structure.
Insert Bit Selection
The decision to run a specific insert bit can only be based on experience
and judgment.
General considerations are:
1. Select a tungsten carbide bit with chisel crest inserts when drilling a
formation that is predominantly shale. Use bit type 4-2, 5-2, 6-1 or 6-2.
2. Select a tungsten carbide bit with high offset and chisel inserts if the shale
content of the formation increases and/or the mud density is high. Use
bit type 5-2 or 5-3.
3. Select a tungsten carbide bit with shorter chisel inserts and less offset if
the formations become more abrasive and unconsolidated. Use bit type 6-3
or 6-4.
4. Select a tungsten carbide bit with projectile or conical inserts when drilling
a formation that is predominantly limestone. Use bit type 6-3 or 6-4.
5. Select a tungsten carbide bit with projectile or conical inserts if the sand
content and abrasiveness of the formation increases. Use bits type 7-1 to 8-3.
Specific considerations are:
1. Select a tungsten carbide insert with the greatest amount of offset and the
longest chisel crested inserts when drilling shale and soft limestone.
2. Select a tungsten carbide insert bit with a medium offset and long chisel
crested inserts when drilling sandy shale with limestone and dolomite. Use
bits type 4-1 to 5-3.
3. Select a tungsten carbide insert bit with a minimum offset and projectile
or conical inserts when drilling limestone, brittle shale, nonporous dolomite
and broken formations. Use bit type 6-3 to 7-3.
4. Select a tungsten carbide bit with medium or no offset and chisel crested
inserts when drilling sandy shales, limestones and dolomites. Use bit type
5-3 or 6-4.
5. Select a tungsten carbide insert bit with no offset and conical or double
cone inserts when drilling hard and abrasive limestone, hard dolomite,
chert, pyrite, quartz, basalt, etc. Use bit type 7-4 to 8-3.
Quantitative Method of Bit Selection
This method is based on cost comparison between bit records and the current
bit run.
The following example illustrates the application of cost-per-foot data in
evaluating the economics of insert bits [34].
Example
Determine the economics for insert bits using the data below.
Applicable costs are: