2-Stage underreamer

摘要

PCT No. PCT/GB95/02540 Sec. 371 Date Jul. 22, 1997 Sec. 102(e) Date Jul. 22, 1997 PCT Filed Oct. 31, 1995 PCT Pub. No. WO96/13648 PCT Pub. Date May 9, 1996A 2-stage underreamer for use in a subterranean wellbore includes a unitary body having upper and lower blades mounted in slots formed perpendicular to each other in the body. Separate upper and lower piston assemblies are provided for driving the blades respectively from a storage configuration in which they are located substantially completely within the slots to a use position. The blades each include a steel arm having mounted thereon a base of tungsten nickel cobalt matrix in which diamond and/or tungsten carbide inserts are provided. A signal is given to the surface that the blades are in their extended position by changing the mud.