Anti-whirl underreamer

A rotary underreamer for enlarging a sidewall of a borehole within an underground formation from a first diameter to a second diameter, comprising:

• a body for connection to a drillstring;
• at least two arms carried by said body and radially extendable between a retracted position for passing the underreamer through the sidewall having the first diameter and a projected position, wherein the distal ends of the arms extend beyond the sidewall having the first diameter to enlarge the borehole to the second diameter;
• means carried by said body for extending said arms between the retracted position and the projected position;
• means for retracting said arms, comprising:
• a spring;
• and
• a slidable piston assembly carried on said spring and having a first set of teeth which mesh with a second set of teeth located on said extendable arms, said spring biasing said slidable piston to cause said arms to be biased to said retracted position;
• a plurality of cutting elements carried on one of said arms for cutting an axially extending cylindrical sidewall of the borehole having the second diameter and for applying a resultant radial force to said body as it rotates;
• and
• a low friction bearing means carried on another of said arms for transmitting said resultant radial force from said body to the sidewall of the borehole, said cutting elements being positioned to ensure said resultant radial force is of sufficient magnitude and direction to substantially maintain said low friction bearing means in contact with the borehole as the underreamer is rotated within the borehole:

A drilling apparatus for forming a second section of borehole in an underground formation, the second section of borehole having a diameter larger than a first section of borehole and axially extending beyond the first section of borehole, the apparatus comprising:

• a rotary underreamer comprising:
• a body having an upper end configured for connection to a drillstring and a lower end configured to receive a drill bit, said body having an instantaneous center of:
• rotation as the drilling apparatus is rotated within the borehole;
• a plurality of arms radially extendable between a retracted position, which allows the underreamer to be passed through the first section of borehole and a projected position, wherein the distal ends of the arms extend radially beyond the sidewall of the first section of borehole;
• means carried by said body for moving said arms;
• a plurality of cutting elements carried on one of said arms for cutting an axially extending cylindrical sidewall of the borehole and for applying a resultant radial force to said body as it rotates;
• and
• a low friction bearing means located on another of said arms for transmitting said resultant radial force from said body to the sidewall of the borehole, said cutting elements being positioned to provide said resultant radial force of sufficient magnitude and direction to maintain said instantaneous center of rotation of said body substantially coincident with the centerline of the borehole as the drilling apparatus is rotated within the borehole;
• and
• an anti-whirl drill bit coupled to said underreamer at said lower end of said body of said underreamer said anti-whirl drill bit having a bearing zone for receiving a second resultant radial force developed by said anti-whirl drill bit as said anti-whirl drill bit rotates within the borehole.

A method of underreaming a borehole in an underground formation from a first diameter to a second diameter which is larger than the first diameter, the method comprising the steps of:

• a) lowering a rotary underreamer attached to a rotational drive source into the borehole to the region of the borehole to be underreamed, the rotary underreamer having:
• at least two arms that are radially movable between a retracted position, for passing the underreamer through a section of the borehole having the first diameter, and a projected position, wherein the distal end of the arms extend radially beyond the sidewall of a borehole having the first diameter;
• a plurality of cutting elements carried on one of said arms for cutting an axially extending cylindrical sidewall of the borehole;
• and
• a low friction bearing means located on another one of said arms for transmitting a resultant radial force to the sidewall of the borehole;
• b) rotating said underreamer while extending said arms to said projected position to enlarge the cylindrical sidewall of the borehole to the second diameter, said cutting elements being positioned to develop said resultant radial force as said underreamer is rotated within the borehole, said resultant radial force being of sufficient magnitude and direction to substantially maintain said low friction bearing means in contact with the borehole as said underreamer is rotated within the borehole.;
• and
• c) applying a forward force to said underreamer while rotating said underreamer to extend the length of the borehole having the second diameter.

A rotary underreamer for enlarging a sidewall of a borehole within an underground formation from a first diameter to a second diameter, comprising:

• a body for connection to a drillstring;
• a maximum of two arms carried by said body and radially extendable between a retracted position for passing the underreamer through the sidewall having the first diameter and a projected position, wherein the distal ends of the arms extend beyond the sidewall having the first diameter to enlarge the borehole to the second diameter;
• means carried by said body for moving said arms;
• a plurality of cutting elements carried on a first arm for cutting an axially extending cylindrical sidewall having the second diameter and for applying a resultant radial force to said body as it rotates;
• and
• a low friction bearing means carried on a second arm located approximately 120 degrees behind said first arm as measured about the axis of rotation of the;
• underreamer, said low friction bearing means capable of transmitting said resultant radial force from said body to the sidewall of the borehole, said cutting elements being positioned to ensure said resultant radial force is of sufficient magnitude and direction to substantially maintain said low friction bearing means in contact with the borehole as the underreamer is rotated within the borehole.