Abstract: An underreamer for increasing the diameter of a bore. The underreamer includes a substantially cylindrical body having an axial bore therein. A mandrel may extend axially through the axial bore. One or more cutter blocks are movably coupled to the body. A ratio of a height of the cutter block to a diameter of the body is between about 0.35:1 and about 0.50:1.

Abstract: An underreamer for increasing the diameter of a bore. The underreamer includes a substantially cylindrical body. A mandrel may extend axially through the body. One or more cutter blocks are movably coupled to the body. A ratio of a height of the cutter block to a diameter of the body is between about 0.35:1 and about 0.50:1.

Abstract: A method to drill a wellbore includes positioning a cutting structure proximal to a distal end of a drilling string, deploying a bottom hole assembly through a central bore of the distal end of the drilling string and the cutting structure, engaging the cutting structure with the bottom hole assembly, and rotating the cutting structure with the bottom hole assembly. An under reamer assembly includes a reamer shoe positioned proximal to a distal end of a drilling string and a cutting structure coupled to the reamer shoe, wherein the cutting structure is configured to be engaged by a bottom hole assembly, and wherein the cutting structure is configured to enlarge a pilot bore cut by a drill bit of the bottom hole assembly.

Abstract: An underreamer for increasing the diameter of a bore. The underreamer includes a substantially cylindrical body. A mandrel may extend axially through the body. One or more cutter blocks are movably coupled to the body. A ratio of a height of the cutter block to a diameter of the body is between about 0.35:1 and about 0.50:1.

Abstract: A downhole tool has a body with a bore formed at least partially therethrough. A cutter block may be coupled to the body and move radially outward from the body in response to an increased pressure in the bore. The cutter block may include an outer surface that transitions from a first portion to a second portion, with the first portion being downhole of the second portion. A radius of curvature between the first and second portions may be less than about 7 cm. The second portion or a line tangential thereto may be oriented at an angle from about 60° to about 120° with respect to a central longitudinal axis of the body. A plurality of cutting elements may be disposed on the outer surface of the cutter block. At least one of the cutting elements may be disposed at least partially on the first or second portion of the outer surface.

Abstract: An underreamer for increasing the diameter of a bore. The underreamer includes a substantially cylindrical body having an axial bore therein. A mandrel may extend axially through the axial bore. One or more cutter blocks are movably coupled to the body. A ratio of a height of the cutter block to a diameter of the body is between about 0.35:1 and about 0.50:1.