Considerations When Designing Tricone Bits

Tricone 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.

Shortly after the great success at Spindletop and Howard Hughes' contribution of the bi-cone bit, roller cones have long been the mainstay of the oil and gas drilling.

Although PDC cutters have, for the most part, replaced tungsten carbide inserts, the Big Four - Hughes, Smith, Reed and Halliburton - still employ the best bit design engineers.

Below are just a few considerations these design engineers must take into consideration:

1. Journal Angle - Journal angle 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.

2. Cone Offset - Increased rate of penetration (ROP) can be achieved by offsetting the ceterline of the cone away from the center of bit rotation. This produces more on-bottom action. The higher the offset the greater the scraping and gouging action on bottom.

a. Soft Formation Roller Cones are designed with greater offset, thereby increasing the gouging and scraping action of the tungsten carbide inserts.

b. Medium Formation Roller Cones employ less offset. This design feature combines tearing and twisting action with crushing and chipping action.

c. Hard Formation Roller Cones employ little or no offset and break rock by a crushing action.

3. Cone Angle - 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.

4. Oversize Angle - Oversize angle 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. This reduces the action on gage and also reaming of gage inserts.

5. Intermesh - Intermesh is 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.

6. Projection and Pitch - Projection is the height of the button or tooth. Pitch is the space between teeth or inserts.

Related Pages:

API Standards:  API standards, including pin sizes for drill bits and acceptable tolerances for rock bits and pdc bits.  

Atlas Copco:  Atlas Copco bit selection guide, examples of shirttail protection, and TCI and steel tooth cutting structure. 

Button Bits:  Button bits offer several advantages over PDC drill bits: they are less expensive and can withstand higher impact.

Drag Bits:  Drag Bits manufactured as one solid piece of alloy steel offer greater durability and reliability.  Available in step and chevron styles for hard rock drilling.

Dull Grading:  Dull grading drill bits is important but often overlooked.  This process provides valuable information for proper bit selection.

IADC:  The IADC classification system for tooth and button bits explained as well as dull grading codes and what they mean.

IADC Classification:  The IADC classification system for PDC bits:  pictures and explanation of what it means and how to use it.

PDC Cutters:  Because of PDC cutters, PDC bits drill sixty-five percent of total footage.  Their shearing action is more efficient than the crushing action of tricones.

PDC Drill Bits:  Available in either matrix or steel bodies, PDC drill bits  offer higher rate of penetration than tricones in many different formations.

Tricones:  With the exception of cutting structure, tricone bits are designed in the same manner regardless of manufacturer. 

Well Completion Bits:  Well completion drill bits from Atlas Copco in both tooth and button bits.  Bear Claw, Hurricane, Aardvark, and PDC diamond mill bits from KC Bit & Supply.



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