Abstract: An underreamer tool has a body with upper and lower portions having an upper cutter blade slot extending transversely through the upper portion and a lower cutter blade slot extending transversely through the lower portion at a right angle thereto. The upper and lower portions have central bores separated by a wall and connected by upper and lower fluid flow passageways bypassing the cutter blade slots. An upper pair of cutter blades mounted in the upper cutter blade slot and a lower pair of cutter blades mounted in the lower cutter blade slot move between a retracted position within the slots and an extended position outward therefrom. An upper piston in the central bore above the upper cutter blade slot has its bottom end engaged on the upper cutter blades and a lower piston in the central bore above the lower cutter blade slot has its bottom end engaged on the lower cutter blades.

Abstract: An underreamer tool has a generally cylindrical body with a threaded top end for connection to a tubing string, a threaded lower portion to receive a drill bit, and a longitudinal fluid passageway extending centrally through the body. The body has three flat surfaces formed on its exterior in circumferentially spaced relation to define a generally triangular cross section intermediate the top and bottom ends of the body. A cutter blade is pivotally mounted on each of the flat surfaces. A piston is slidably received in a bore in the upper portion of the body and has central fluid passageway therethrough. Push rod members are connected to the piston inside the body and each has an exterior portion slidably mounted in a slot on the exterior of the body engaging the cutter blades for moving them between a retracted position against the body and an extended position outward therefrom.

Abstract: An underreamer tool has a body with upper and lower portions having an upper cutter blade slot extending transversely through the upper portion and a lower cutter blade slot extending transversely through the lower portion at a right angle thereto. The upper and lower portions have central bores separated by a wall and connected by upper and lower fluid flow passageways bypassing the cutter blade slots. An upper pair of cutter blades mounted in the upper cutter blade slot and a lower pair of cutter blades mounted in the lower cutter blade slot move between a retracted position within the slots and an extended position outward therefrom. An upper piston in the central bore above the upper cutter blade slot has its bottom end engaged on the upper cutter blades and a lower piston in the central bore above the lower cutter blade slot has its bottom end engaged on the lower cutter blades.