Apparatus for drilling a curved subterranean borehole

Abstract

A curve drilling assembly operable with a rotary drill string is provided for drilling a curved subterranean borehole. The assembly includes a curve guide, a rotary drill bit, an imbalance force assembly, and a bearing assembly. The curve guide is connectable with the drill string for deflecting the drill string toward the outside radius of the curved borehole. The imbalance force assembly, which preferably is provided by selectably disposing cutting elements on the drill bit, is rotatable with the drill string for creating a net imbalance force along a net imbalance force vector substantially perpendicular to the longitudinal axis of the drill bit during drilling. The bearing assembly is rotatable with the drill string and is located in the curve drilling assembly near the cutting elements of the drill bit for intersecting a force plane formed by the longitudinal bit axis and the net imbalance force vector and for substantially continuously contacting the borehole wall during drilling. Preferably, the bearing assembly includes a substantially smooth wear-resistant sliding surface. The curve guide includes a mandrel rotatably disposed within a housing. A contact ring may be provided at either the uphole or the downhole end of the mandrel for contacting the borehole wall and supporting the radial force component created by the deflection of the drill string at the end of the mandrel. A flexible joint may be connected to the end of the mandrel adjacent the contact ring for drilling curved boreholes having a short radius of curvature.