Drag bits have a wide range of drilling applications including environmental, exploration, geothermal, water well, road construction, and natural gas and oilfield drilling.
The best application for drag bits is in softer, unconsolidated formations like clays, shale, sands, and soft limestone.
The most common styles are either step type or chevron type bits.
Step Drag Bit
Drill overburdens with sands, clays and soft formations with a step drag bit.
The more aggressive cutting structure will produce larger cuttings than a chevron style bit and with higher ROP. However, it's less durable as well.
For best drilling results, maintain rotary table speeds between 60 and 80 rpm with light weight on bit (WOB).
Chevron Drag Bit
Drill more abrasive formations, like soft sandstones and shales, with a chevron drag bit.
The cutting structure is more durable than the step drag bit but will also penetrate more slowly.
For best drilling results, maintain rotary table speeds between 50 and 60 rpm with light to medium weight on bit (WOB). Harder formations require more WOB.
3 wing, 4 wing, or Step?
We’ve created the following table to help you decide which type of drag bit is needed for your application.
|3 Wing||4 Wing||Step|
|Very hard rock/|
to be logged
Simply put, 4 wing bits are the most durable BUT have the lowest ROP. When making a decision on which drag bit to buy, however, don't purchase a 3 wing or step just to be able to drill faster. Always remember that damaged carbide cutters slow penetration rates.
Kelly bits are commonly used for table drive rigs. Common threads are 2 3/8 IF, Mayhew regular, Failing or Mayhew Junior, and their extremely long gauges help condition the hole.