Patent ID: 6220372
Filing Date: 2001-04-24
Classification: E21B

Abstract:
In a drilling apparatus comprising a flexible shaft directable down a wellbore extending downwardly into a subterranean formation, the flexible shaft having an upper driving end and a lower driven end, the flexible shaft being driven by a rotary drive and being axially movable in the wellbore for drilling therefrom, the improvement comprising:a helical outer coil spring and one or more smaller helical inner coil springs residing concentrically within the outer coil spring for forming the flexible shaft, each of the outer and inner coil springs being formed of wire having a substantially circular cross-section and each successively smaller inner coil spring having an outer diameter substantially the same as the inner diameter of the adjacent larger coil spring, each coil spring being wound opposite in direction to that of the next adjacent coil spring, and all coil springs being held in rigid relation to each other coil spring at the flexible shaft's driven and driving ends;a cutting bit at the driven end of the flexible shaft, the direction of the bit's rotation being co-ordinated with the outer coil spring so that torque causes the outer coil spring to tighten on the one or more inner coil springs;a shaft guide conduit forming an elbow having upper and lower ends through which the flexible shaft extends for diverting the flexible shaft from a path substantially parallel to the wellbore to one extending laterally;anti-friction means within the elbow for enabling the flexible shaft to move therethrough without restricting either rotation or axial movement therethrough; andan anchor for the shaft guide conduit within the wellbore.