Steerable directional drilling reamer

A reamer for use in horizontal directional drilling, the reamer comprising:

• a drive shaft;
• a front coupling disposed on a front end of the drive shaft, the front coupling configured to removably couple the reamer to a drill string;
• a carrier frame mounted about the drive shaft;
• a mixing element disposed on the drive shaft;
• a sun gear disposed on the drive shaft;
• at least one planet gear rotatably mounted to the carrier frame, the planet gear engaging the sun gear;
• a ring gear having a reaming surface, the ring gear being rotatably driven by the planet gear;
• wherein when the drive shaft is rotated, torque is transferred to the mixing element and to the ring gear through the sun gear and planet gear such that the ring gear is rotated at fewer revolutions per minute than the drive shaft and the mixing element.

A method for backreaming a pilot bore in horizontal directional drilling, the method comprising:

• running a drill string with a distal end through the pilot bore;
• coupling a backreamer including a mixing element and a reaming surface to the distal end of the drill string;
• pumping drilling fluid to the backreamer;
• rotating the reaming surface at a first speed while simultaneously rotating the mixing elements at a second speed faster than the first speed;
• drawing the rotating drill string and backreamer along the length of the pilot bore;
• and
• mixing the drilling fluid with dirt and cuttings into a slurry and displacing the slurry from the pilot bore.

A reamer assembly adapted to be driven by a drill string, the reamer assembly comprising:

• a reamer having a reaming surface;
• a torque transfer gear system for transferring torque from the drill string to the reamer, the torque transfer gear system being configured to rotate the reamer at a different speed than the drill string;
• and
• a mixing element coupled to the torque transfer gear system.

A steerable reamer for use in horizontal directional drilling, the reamer comprising:

• a cutting body having a front end and a back end and defining an axis of rotation;
• a front coupling configured to removably couple the front end of the cutting body to a drill string;
• a steering shaft having a front end and a back end, the front end of the steering shaft being rotatably coupled to the back end of the cutting body and centered on the cutting body's axis of rotation, the back end of the steering shaft being offset from the cutting body's axis of rotation;
• and
• a rear coupling configured to removably couple the back end of the steering shaft to a ream line.

A steerable reamer for use in horizontal directional drilling, the reamer comprising:

• a drive shaft characterized by an axis of rotation and configured to be removably coupled to a drill string;
• a carrier frame offset mount rotatably coupled to the drive shaft, the carrier frame offset mount configured to be coupled to a ream line such that a longitudinal axis of the ream line is not collinear with the axis of rotation of the drive shaft;
• a sun gear disposed on the drive shaft;
• at least one planet gear rotatably mounted to the carrier frame offset mount, the planet gear engaging the sun gear;
• a ring gear having a cutting surface rotatably coupled to the drive shaft, the ring gear being rotatably driven by the planet gear;
• wherein when the drive shaft is rotated, torque is transferred to the ring gear through the sun and the planet gears.

A method for horizontal directional drilling, the method comprising:

• drilling a pilot bore from an entry point to an exit point with a drilling machine;
• connecting a reamer having an offset mount to a drill string which extends through the pilot bore at the exit point;
• positioning an anchor machine at the exit point of the pilot hole;
• connecting a ream line both to the reamer by means of the offset mount and to the anchor machine such that the anchor machine prevents the ream line from rotating;
• propelling the reamer back along the pilot bore by cooperation of the drilling machine and the anchor machine thereby reaming a hole, the anchor machine adding to the length of the ream line in the hole while the drilling machine is reducing the length of the drill string;
• and
• removing the reamer when the reamer exits at the entry point.