New Assembly Drills Without Reactive Torque
Authors: Southard Robert 
Published: December 2007

A new tool has been designed, built, and tested that virtually eliminates the reactive torque normally produced from drilling directionally with a motor. The elimination of reactive torque while drilling directionally with a motor marks a significant improvement over current motor drilling. Using this new technology, known as the "Planetary Bit Driver," the tool face can be quickly and easily set in the desired direction and drilling can continue in that direction regardless of drilling parameters, drilling conditions, or lithology.

Benefits of drilling without reactive torque include: It is quick and easy to set the tool face in the desired direction.No time is wasted waiting on tool face updates after the direction is set.No time is wasted resetting the tool face after motor stalls, changing azimuth, making a connection, etc.Smaller, reliable, and consistent dog-leg severities can be achieved.High torque motors can be utilized.Aggressive PDC bits on motors can be utilized.Fewer trips for more aggressive bits are needed after directional work is completed.More tortuous well paths can be drilled.Pilot/Reamer drilling performance.Higher ROP result from all the above.

Reactive torque is eliminated in the Planetary Bit Driver by utilizing two, concentric, counter-rotating bits, instead of a single right-turning bit on a conventional motor-powered directional drilling assembly. The counter-rotation is accomplished by the use of a set of planetary gears. Splines on the drive shaft on the motor turn the planetary gears, which mesh with a ring gear to produce counter-rotation to the outer bit. The Planetary Bit Driver is made up to a standard motor at the bit box and is anchored to the motor housing at the stabilizer sleeve threaded connection. A standard fixed-cutter bit is used for the center, clockwise rotating bit. The outer bit is a specially-designed, counter-clockwise rotating bit with PDC cutters built to match the inner bit. The inner bit drills a smaller diameter (6.75" in this test case), and the outer bit drills the remainder of the hole (6.75" – 8.75" in this test case).

In a preliminary test performed at a test rig in Houston, Texas, cement was drilled out of 9-5/8" casing. This test confirmed that the Planetary Bit Driver will effectively drill and that virtually no reactive torque is produced while drilling. Data recorded during the test and presented in this paper shows that the Planetary Bit Driver did not produce significant reactive torque and operated much more smoothly than a conventional bit with less stick/slip. A design flaw in the carrier of the tool's first prototype resulted in only two of the six planetary gears fitting in the carrier, which caused a premature failure of the planetary gear assembly after drilling twelve (12) feet. The Planetary Bit Driver has been subsequently redesigned and manufactured with the proper six gear configuration, larger and more robust gear shafts, and PDC cutters for drilling rock formations. The second prototype of the Planetary Bit Driver is now complete, and we are preparing for a second test.