Tricone Drill Bits Design

In specific applications, tricone drill bits maintain their relevance despite the prevalence of PDC bits, particularly in vital areas like the Barnett Shale. To effectively compete in offshore or natural gas drilling sectors, manufacturers must carefully consider various factors when designing rock bits, including downhole vibrations. Design engineers must meticulously analyze several key considerations, including:

• Journal angle: Determines the overall aggressiveness of the bottom hole profile, with softer formations employing a 33-degree angle and harder formations employing a 36-degree angle.
• Cone Offset: Offsetting the cone’s centerline from the bit’s rotation center increases the rate of penetration (ROP), resulting in more efficient on-bottom action. Soft formation roller cones utilize greater offsets to enhance gouging and scraping action, while medium formation cones employ less offset for a combination of tearing, twisting, crushing, and chipping action. Hard formation cones typically have little to no offset and primarily rely on crushing action.
• Cone Angle: Soft to medium formation tricones feature a rounder cone profile and larger cone angle, promoting gouging and scraping action. In contrast, hard formation bits have a smaller cone angle and flatter cone profile, facilitating crushing action.
• Oversize Angle: This controls the cone diameter at the gage. Soft formation tricones utilize a higher oversize angle for increased gage action and diameter. Hard formation bits have minimal to no oversize angle, reducing gage action and reaming of gage inserts.
• Intermesh: Determines the distance a tooth or insert extends into adjacent cone grooves, allowing for formation cleaning and preventing packing.
• Projection and Pitch: Refers to the height of the button or tooth and the spacing between teeth or inserts.

Fluid Circulation

All rock drill bits require some type of fluid circulation. Drilling fluid may consist of water or oil, air, or foam. The circulation of drilling fluid serves several purposes:

• Drills new geological formations by clearing away cuttings
• Stabilizes the borehole wall
• Cleans and cools the bit

Bearing Types

Tricones have various bearing types, including roller or open bearings, sealed roller bearings, and friction bearings or sealed journal bearings.

Roller or open-bearing

This bearing type is commonly used in various applications such as well workovers, shallow oil and gas drilling, water well drilling, and mining. It consists of both ball and roller bearings, allowing the cones to rotate freely. The drilling fluid helps cool these bearings. Open-bearing bits are often repairable unless the race inside the cone is severely worn.

Open-bearing bits can be identified by their IADC code, typically ending with a number 1, 2, or 3.

(Read more about the IADC Classification System)

Sealed Roller Bearing

The main distinction between a sealed roller bearing and an open-bearing drill bit is the presence of a seal around the bearings, which shields them from cuttings and debris.

Sealed roller-bearing bits are commonly utilized in mining, natural gas drilling, geothermal operations, and certain oilfield exploration activities. Even after the seal wears out and loses effectiveness, the drill bit retains some functionality and operates similarly to a roller-bearing drill bit.

The IADC Classification easily distinguishes sealed roller bearing bits because the final number will either be a 4 or a 5.

Friction-bearing or sealed journal-bearing

This bearing type is primarily utilized in oil well and natural gas drilling operations. Despite its higher cost, it is known for its ability to endure significant abuse. Instead of roller bearings, a floating bushing is used inside the cone. This bearing type is also grease-lubricated and sealed to prevent external debris from entering.

Friction-bearing bits are commonly employed in directional drilling applications. Gage inserts placed on the bit shank help reduce excess shank wear. Reused or refurbished sealed bearing bits are predominantly used in water well drilling and some oil and gas operations.

The IADC Classification System of Tricones easily distinguishes journal bearing bits just by identifying the final IADC number – it will either be a 6 or a 7.

Understanding and optimizing these design aspects are crucial for manufacturers aiming to deliver high-performance tricone drill bits tailored to specific drilling requirements in diverse geological conditions.