PDC Bit Operating Parameters
PDC bits do not have the benefit of the self fluid-cleaning action between
rows of teeth like roller cone bits, so they must rely on the bit’s hydraulics
to flush the cuttings from under the bit to prevent balling. This is
accomplished with strategically positioned converging-diverging nozzles
which maximize cleaning while minimizing erosion of the body near the
nozzle area. Optimum hydraulic range is between 2.0 to 4.0 hydraulic
horsepower per square inch. The interchangeable jet nozzles come in
standard sizes from 8/32’s to 14/32’s.
Bit life is controlled by the cutting structure. As stated earlier, the PDC
cutting elements provide a self-sharpening edge with the wear resistance of
diamonds. This combination is very effective in soft to medium formations
such as shale, chalks, limestones, clays, salts and anhydrite. These
formations have been drilled at excellent penetration rates with weights
between 1000 and 2500 pounds per inch of bit diameter and rotary speeds
of 85 to 140 rpm. Economic performance has also been achieved with
rotary speeds of 750 rpm and weights of 1000 pounds per inch of bit
diameter using downhole motors.
High rotary speeds provide better drill rates and reduce the chances of
deviation. Optimum rotary speed varies with formation hardness. A soft,plastic formation would require higher rpm; a hard formation, lower rpm.
Most applications require rotary speeds less than 120 rpm.
Lighter weight-on-bit means lower stress on the drill string, with increased
string life as a result. There's less drag in directional holes because fewer
drill collars are required, reducing the potential for stuck pipe.
These bits have made economical runs in both oil and water base muds. Oil
base muds and the addition of lubricants to water base muds will enhance
PDC bit performance in formations that tend to be somewhat plastic and
sticky.
Formations which should be avoided with PDC bits are soft sticky shales
and clays, abrasive sands, and those formations which are very hard. In
sticky formations, PDC bits have a tendency to ball up; in abrasive
formations or hard formations, cutter wear and breakage occur rapidly.
PDC bits cannot drill as broad a range of formations as roller cone bits, but
have shown to be competitive with diamond bits. Thus, care must be taken
when selecting bits for various applications. When properly applied, most
PDC bits can be run in more than one well.
PDC bits cost between $10,000 to $25,000, and savings are measured in
terms of trip time saved, longer bit life, improved rates of penetration, and
fewer rig hours required to drill a well.
PDC bits do not have the benefit of the self fluid-cleaning action between
rows of teeth like roller cone bits, so they must rely on the bit’s hydraulics
to flush the cuttings from under the bit to prevent balling. This is
accomplished with strategically positioned converging-diverging nozzles
which maximize cleaning while minimizing erosion of the body near the
nozzle area. Optimum hydraulic range is between 2.0 to 4.0 hydraulic
horsepower per square inch. The interchangeable jet nozzles come in
standard sizes from 8/32’s to 14/32’s.
Bit life is controlled by the cutting structure. As stated earlier, the PDC
cutting elements provide a self-sharpening edge with the wear resistance of
diamonds. This combination is very effective in soft to medium formations
such as shale, chalks, limestones, clays, salts and anhydrite. These
formations have been drilled at excellent penetration rates with weights
between 1000 and 2500 pounds per inch of bit diameter and rotary speeds
of 85 to 140 rpm. Economic performance has also been achieved with
rotary speeds of 750 rpm and weights of 1000 pounds per inch of bit
diameter using downhole motors.
High rotary speeds provide better drill rates and reduce the chances of
deviation. Optimum rotary speed varies with formation hardness. A soft,plastic formation would require higher rpm; a hard formation, lower rpm.
Most applications require rotary speeds less than 120 rpm.
Lighter weight-on-bit means lower stress on the drill string, with increased
string life as a result. There's less drag in directional holes because fewer
drill collars are required, reducing the potential for stuck pipe.
These bits have made economical runs in both oil and water base muds. Oil
base muds and the addition of lubricants to water base muds will enhance
PDC bit performance in formations that tend to be somewhat plastic and
sticky.
Formations which should be avoided with PDC bits are soft sticky shales
and clays, abrasive sands, and those formations which are very hard. In
sticky formations, PDC bits have a tendency to ball up; in abrasive
formations or hard formations, cutter wear and breakage occur rapidly.
PDC bits cannot drill as broad a range of formations as roller cone bits, but
have shown to be competitive with diamond bits. Thus, care must be taken
when selecting bits for various applications. When properly applied, most
PDC bits can be run in more than one well.
PDC bits cost between $10,000 to $25,000, and savings are measured in
terms of trip time saved, longer bit life, improved rates of penetration, and
fewer rig hours required to drill a well.
