Tricone Drill Bits Design
Tricone drill bits continue to demonstrate their usefulness in certain applications, even though pdc bits have taken over most of the drilling in important areas such as the Barnett Shale.
For manufacturers to successfully compete in the offshore or natural gas drilling market, much has to be considered when designing rock bits, such as downhole vibrations.
Below are just a few considerations design engineers must take into consideration: –
Determines the overall aggressiveness of the bottom hole profile. Soft formation rock bits employ a 33 degree angle while hard formation rock bits employ a 36 degree angle.
Offsetting the centerline of the cone away from the center of bit rotation increases rate of penetration (ROP) producing more on-bottom action. Therefore, the higher the offset the greater the scraping and gouging action on bottom.
Greater offset design for soft formation roller cones increases the gouging and scraping action of the tungsten carbide inserts.
Medium Formation Roller Cones employ less offset. This design feature combines tearing and twisting action with crushing and chipping action.
Hard Formation Roller Cones employ little or no offset and break rock by a crushing action.
Soft to medium formation tricones employ a more round cone profile and a larger cone angle. This creates a bottom hole action of gouging and scraping. Hard formation bits employ a smaller cone angle and a flatter cone profile. This creates a bottom hole action of crushing.
Controls the diameter of the cone at gage. Soft formation tricones employ a higher oversize angle thus escalating gage action and cone diameter. Hard formation bits have very little or no oversize angle reducing the action on gage and also the reaming of gage inserts.
The distance the top of a tooth or button bit insert extends into the grooves of adjacent cones. This spacing allows for cleaning of formation and prevents packing.
Projection and Pitch
The height of the button or tooth, and the space between teeth or inserts.