Button Bits Can Drill Formations PDC Bits Cannot

Button bits are still a mining and drilling tool used in hard rock drilling even though the PDC drill bit has taken over more than half the market share of total footage drilled.

Important Features of a Button Bit

Even though the PDC bit is wildly popular, tricone bits aren't so easily pushed aside.

For instance, PDC bits currently do not drill gravels, dolomite, and hard limestone very well, if at all.  It seems that the need for tricones will continue for a while.

Since the important gusher at Spindletop and the invention of the bi-cone bit by Howard Hughes, Sr.,  roller cones have played an important role in mining and drilling.

Roller cones have rotating cones that contain tungsten carbide inserts. Tricone, or three cone bits, are the most common; however, two cone and one cone bits are also manufactured but aren't used very often.  

TUNGSTEN CARBIDE INSERT DESIGN

Button bit inserts fall in two classifications: chisel and conical

Chisel Style Button Bit

Chisel inserts are more aggressive than conical, and some designs employ a mixture of both.



Conical Shaped Button Bit Inserts

Conical inserts are more domed in appearance and are used to grind formations that are more abrasive and are higher in compressive strength.

Tungsten carbide inserts are individually manufactured and then press fit into pre-drilled holes in the cone of the bit.

Although tungsten carbide inserts are the mainstay of roller cones, pdc cutters and their use in pdc bits are fast replacing them.

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:

*Clears away cuttings so new geological formations can be drilled

*Stabilizes the borehole wall

*Cleans and cools the bit

BEARING TYPES

There are three main types of bearings found in tricones. They are:

Roller or open bearing. This bearing type is commonly used in well workover applications, shallow oil and gas drilling, water well drilling and mining applications. Atlas Copco and Focus Rock Bit manufacture one of the best on the market today. This bearing type allows the cones to spin freely. The bearing itself consists of a row of ball bearings and a row of roller bearings. These bearings are cooled by the drilling fluid in use. A roller bearing can be repaired until the race inside the cone becomes worn too badly.

Open bearing bits are easily distinguished by its IADC code with the final number being either a 1, 2 or 3. One is open bearing without shank protection, two is without shank protection and suitable for air drilling, and three is with shank protection.

Sealed Roller Bearing This bearing type is basically the same as an open bearing with the exception that there is a seal around the bearings to protect from cuttings and debris.

Sealed roller bearing bits are used in mining, natural gas drilling, geothermal and some oilfield exploration. Once the seal is worn and is no longer good, the drill bit still has some life left and will perform like an roller bearing drill bit.

Sealed roller bearing bits are easily distinguished through the IADC Classification of Tricones because the final number will either be a 4 or a 5. Four denotes sealed roller bearing without shank protection, five is with shank protection.

Friction bearing or sealed journal bearing This is the most commonly used bearing type for oil well and natural gas drilling. Although the cost is generally higher, this bearing type can withstand the most abuse. The roller bearings inside the cone are replaced with a floating bushing. The bearing is also grease lubricated and sealed from outside debris.

Friction bearing bits are frequently used in directional drilling applications.Due to the extra wear on the shank, gage inserts are placed on the shank for extra protection.

Journal bearing bits are easily distinguished by the IADC Classification System of Tricones. The final IADC number will either be a 6 or a 7. Six is a sealed journal bearing without shank protection and seven is with shank protection.




BUTTON BITS VS. PDC

Advantages

*Cost - Initially cheaper investment

*Less Impact Damage - Impact is less damaging to the cutting structure 

*Better in Hard Rock Formations - The fracturing action of a button bit is better in non-homogeneous rock formations.

*More Control Over the Bit - In directional drilling applications, a button bit is easier to control offering lower torque, greater flexibility on WOB and a more steady tool face.

*Design of Button Bits Many years of experience has given manufacturers the lead in designing button bits for abrasive and difficult formations.

***Note:Button bits have traditionally been used for directional drillingbecause they're steerable. However, new technology has caused the pdc bit to out perform.

Why?

Special emphasis has been placed on the pdc cutter and design aspects of the pdc bit.




Disadvantages

*Lost Cones - Because tricones have moving parts, there is always the risk of losing a cone in the hole.

*Lower ROP - The shearing action of a PDC bit is more efficient, resulting in higher ROP.

*Higher Cost Per Foot - Lower ROP results in higher cost per foot. PDC bits can be repaired and run multiple times, tricones cannot.

*Lower Bit Life - Tricones will need to be replaced more often than PDC drill bits.





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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