Downhole sub for directional drilling

摘要

A downhole sub for use in directional drilling with a bent sub attached to a drill bit. The drill bit is operated by a downhole motor. The downhole sub includes upper and lower tubular sections whose centers are offset from one another in the bend direction of the bent sub. The downhole sub includes an intermediate tubular section disposed between the upper and lower tubular sections, with the bore of the intermediate section included within overlap between extensions of each of the bores of the upper and lower tubular sections. The axes of the upper and lower tubular section are parallel and offset between about +E,fra 1/4+EE inch and 2 inches. The intermediate section grades gradually into the upper and lower tubular sections. The downhole sub is used by incorporation into a drill string above the bent sub and spaced from the bend sufficiently to allow the drill string to use the downhole sub as a lever to force the drill bit into the wall of the borehole.