PDC Bit Drilling Parameters
Even though PDC bits have achieved recognition as a viable tool for
improved drilling, certain precautions and drilling parameters should be
met in order that the bit run be as efficient and economical as possible.
1. When the prior bit is removed, it should be inspected for any
damage. If junk was left in the hole, do not run a PDC bit until
the hole is cleaned.
2. When picking-up a PDC bit, take all the precautions normally
taken when handling a diamond bit, and some additional ones:
a. When removing the bit from its box, handle it carefully. Do
not roll it out on the rig floor. If the bit is dumped on the floor
and some of the cutters are chipped, the bits life will be
reduced.
b. The interior of the bit should be inspected to make sure no
debris is left inside.
c. The proper bit breaker should be used to make up the bit.
3. The bit is one solid piece and does not have the limited flexibility
of roller cone bits. Hitting ledges or running through tight spots
can damage the gauge cutters.
4. If it is necessary to ream when going into the hole, pick up the
kelly and run the maximum flow rate. The rotary speed should be
about 60, and go through the tight spot slowly.
5. When near bottom, the last joint should be washed down slowly
at full flow and 40-50 rpm, to avoid plugging the bit with any fill.
a. To locate the bottom of the hole, observe the torque and
weight indicators. Because of the type of cutting structure on
PDC bits, it is common that the first on-bottom indication is a
sudden increase in torque.
b. After the bottom of the hole has been reached, the bit should
be lifted a foot or two off bottom, then circulate and rotate
slowly for about five minutes to make certain the bottom of
the hole is cleaned.
6. When ready to start drilling, bring the rotary speed up to 60 and
approach bottom. Light weight should be used in order to cut a
new hole pattern.
a. At least 1 foot of new hole should be cut in this manner before
looking for optimum weight and rotary speed for drilling.
b. In soft formations, the bit will drill quickly with light weight,
and the rotary speed should be increased until the bit is
drilling at its fastest rate (usually between 100-150 rpm).
c. In hard formations, it will take much longer to drill the one
foot. Adding weight too quickly will damage the cutters.
Once the bottom hole pattern is established and weight is
added, watch the torque indicator for possible problems.
7. There is no limit to rotary speed, use as much as possible without
damaging the rest of the drillstring.
8. The on-bottom torque should approach what is experienced with
roller cone bits. If there is no torque buildup, or the penetration
rate does not increase with added weight, the formation may not
be suitable for PDC bits.
9. After making a connection, the bit should be washed back down
to bottom. Dropping and then stopping the drillstring suddenly
can cause the bit to hit bottom and be damaged due to pipe
stretch.
10. PDC bits respond dramatically to changing formations, if the rate
of penetration suddenly decreases or the bit starts torquing, a
change in the weight-on-bit and rotary speed should help.
11. When the cutters wear to a point where they will not drill, the bit
should be pulled. If the wear is primarily on the outside, there
will be a sudden decrease in the penetration rate and torque, and
an increase in standpipe pressure. If the wear is on the gauge
portion, there will be very high on-bottom torque with little
weight-on-bit and a decrease in the penetration rate.
Even though PDC bits have achieved recognition as a viable tool for
improved drilling, certain precautions and drilling parameters should be
met in order that the bit run be as efficient and economical as possible.
1. When the prior bit is removed, it should be inspected for any
damage. If junk was left in the hole, do not run a PDC bit until
the hole is cleaned.
2. When picking-up a PDC bit, take all the precautions normally
taken when handling a diamond bit, and some additional ones:
a. When removing the bit from its box, handle it carefully. Do
not roll it out on the rig floor. If the bit is dumped on the floor
and some of the cutters are chipped, the bits life will be
reduced.
b. The interior of the bit should be inspected to make sure no
debris is left inside.
c. The proper bit breaker should be used to make up the bit.
3. The bit is one solid piece and does not have the limited flexibility
of roller cone bits. Hitting ledges or running through tight spots
can damage the gauge cutters.
4. If it is necessary to ream when going into the hole, pick up the
kelly and run the maximum flow rate. The rotary speed should be
about 60, and go through the tight spot slowly.
5. When near bottom, the last joint should be washed down slowly
at full flow and 40-50 rpm, to avoid plugging the bit with any fill.
a. To locate the bottom of the hole, observe the torque and
weight indicators. Because of the type of cutting structure on
PDC bits, it is common that the first on-bottom indication is a
sudden increase in torque.
b. After the bottom of the hole has been reached, the bit should
be lifted a foot or two off bottom, then circulate and rotate
slowly for about five minutes to make certain the bottom of
the hole is cleaned.
6. When ready to start drilling, bring the rotary speed up to 60 and
approach bottom. Light weight should be used in order to cut a
new hole pattern.
a. At least 1 foot of new hole should be cut in this manner before
looking for optimum weight and rotary speed for drilling.
b. In soft formations, the bit will drill quickly with light weight,
and the rotary speed should be increased until the bit is
drilling at its fastest rate (usually between 100-150 rpm).
c. In hard formations, it will take much longer to drill the one
foot. Adding weight too quickly will damage the cutters.
Once the bottom hole pattern is established and weight is
added, watch the torque indicator for possible problems.
7. There is no limit to rotary speed, use as much as possible without
damaging the rest of the drillstring.
8. The on-bottom torque should approach what is experienced with
roller cone bits. If there is no torque buildup, or the penetration
rate does not increase with added weight, the formation may not
be suitable for PDC bits.
9. After making a connection, the bit should be washed back down
to bottom. Dropping and then stopping the drillstring suddenly
can cause the bit to hit bottom and be damaged due to pipe
stretch.
10. PDC bits respond dramatically to changing formations, if the rate
of penetration suddenly decreases or the bit starts torquing, a
change in the weight-on-bit and rotary speed should help.
11. When the cutters wear to a point where they will not drill, the bit
should be pulled. If the wear is primarily on the outside, there
will be a sudden decrease in the penetration rate and torque, and
an increase in standpipe pressure. If the wear is on the gauge
portion, there will be very high on-bottom torque with little
weight-on-bit and a decrease in the penetration rate.
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