BIT WHIRL And BHA WHIRL (Source: Weatherford Motors HandBook)

Bit Whirl

The eccentric rotation of the bit about a point other than its geometric center created from excessive side cutting forces acting on the bit. The immediate impact of this occurrence is the borehole becoming over gauge and a large increase in impact loading on the PDC cutters resulting in premature bit failure. Bit whirl is commonly seen while drilling with bits that have aggressive side cutters, push the bit rotary steerable systems, hard rock areas, and low angle wells.

Detecting Bit Whirl:

• Increase in lateral / torsional vibrations

• Over gauge hole

• Slower ROP

• Excessive wear / chipped cutters

• Premature bit failure

Mitigating Bit Whirl:

• Use of anti-whirl bit

• Decrease RPM / increase WOB

• Pick up off bottom / work out all torque and vibration

• Increase to full RPM after on-bottom

BIT WHIRL

BHA Whirl

BHA whirl is the eccentric rotation or walk of the BHA around the wellbore. The resulting actions include high torsional and lateral vibrations from repetitive impact of the BHA and wellbore. These actions can lead to several things such as uneven stabilizer wear, tool joint damage, and downhole tool failures. BHA whirl is commonly seen while drilling with pendulum assemblies, poorly stabilized BHA’s, over gauge holes, and in washed out areas.

Detecting BHA Whirl:

• Uneven wear on stabilizer blades

• Increase in surface torque

• Localized wear on tool joints

• Increase in lateral vibrations

Mitigating BHA Whirl:

• Decrease RPM / increase WOB

• Pick up off bottom / work out all torque and vibration

• Use roller reamers in place of stabilizers

• Non-rotating drillstring protectors

BHA WHIRL

ROTARY WHIRL (Source: DrillingOps canal Youtube)