Apparatus and method for drilling and reaming a borehole

A reamer for use in forming a borehole through earthen formations, comprising:

• a housing having a rotational axis and an outer surface;
• an elongate first blade extending from said housing having a plurality of cutter elements mounted for engaging formation material as said housing is rotated, and having a radially outermost surface for contacting the borehole wall, said first blade and said housing forming an eccentric reamer body having a first diameter;
• at least a first movable member on said reamer body having a contact surface for contacting the borehole wall, said first movable member movable from a first position where said contact surface of said movable member falls within the circle defined by said first diameter to a second position where said contact surface of said movable member extends beyond the circle defined by said first diameter;
• and
• wherein said first blade includes first and second ends, a central segment between said ends, and inclined surfaces adjacent to said first and second ends, wherein said cutter elements are disposed on said central segment and on at least one of said inclined surfaces.

A drilling assembly for forming a borehole comprising:

• a mandrel having at lease one fixed blade and having at Least one moveable member mounted in a cavity in said mandrel, said moveable member having a contact surface for engaging the borehole wall;
• said fixed blade extending from said mandrel in a first radial direction and including a plurality of cutter elements disposed on said blade;
• an actuator in said mandrel extending said movable member to an extended position and a retractor in said mandrel retracting said movable member to a contracted position;
• a passageway in said mandrel for communicating pressurized fluid therethrough;
• a bore in said mandrel communicating fluid pressure from said passageway to said actuator for movement of said movable member to said extended position;
• and
• at least one retainer retaining said movable member in said contracted position until a fluid at a predetermined fluid pressure is communicated through said passageway and causes said retainer to release said moveable member.

A drilling assembly for cutting a borehole in earthen formation, comprising:

• a drill bit;
• an adjustable diameter eccentric reamer above said bit having a housing, a fluid passageway through said housing, a fixed blade, and at least one movable member, said movable member actuatable to move from a first where said reamer has a first diameter to a second position where said reamer has a second diameter that is greater than said first diameter;
• a plurality of cutter elements mounted on said blade and having cutting faces oriented to cut formation material as said drilling assembly is rotated;
• at least one latching retainer releasably connecting said movable member and said housing, said retainer holding said movable member in said first position at fluid pressure within said fluid passageway less than a predetermined threshold pressure, and releasing said movable member at a fluid pressure equal to or greater than the predetermined threshold pressure.

A method of passing a drilling assembly through an existing borehole having a given diameter and drilling a new borehole beneath the existing borehole, comprising:

• providing a drilling assembly having a pilot bit with a pilot bit axis and an eccentric reamer above said pilot bit, said reamer including at least one extendable contact member and at least one fixed blade, wherein said fixed blade includes a plurality of cutter elements;
• contracting the contact members of the eccentric reamer and retaining the contact members in the contracted position;
• contacting the existing cased borehole with the fixed blade of the reamer and one side of the pilot bit;
• lowering the drilling assembly to the bottom of the cased borehole;
• extending the extendable contact member of the eccentric reamer;
• rotating the drilling assembly with the extendable contact member of the eccentric reamer in the extended position to form a new borehole beneath the existing cased borehole as the fixed blade having the cutter elements enlarges the pilot hole made by said pilot bit.

A method of reaming a borehole, comprising:

• providing a drilling assembly having a drill bit and an eccentric adjustable diameter reamer above said bit, said eccentric reamer including at least one extendable contact member and a fixed blade, wherein said fixed blade includes a plurality of cutter elements;
• contracting the contact members of the eccentric reamer and retaining them in the contracted position;
• lowering the drilling assembly into the borehole;
• extending the extendable contact members of the eccentric reamer;
• rotating the drilling assembly with the extendable contact members of the eccentric reamer in the extended position.