| 摘要 |
A rotating centralizer and a centralizing bearing assembly are provided in order to maintain a survey instrument assembly at a fixed angular orientation with respect to a core barrel supported by the bottomhole assembly of a rotating drill string and rotationally isolated therefrom. The centralizer comprises a sleeve having an inner bearing surface providing for rotation of the sleeve with respect to a support sub, and outer bearing surfaces located at the ends of four vanes allowing for rotation of the sleeve with respect to the surrounding drill string. The centralizing bearing assembly comprises a hanger sub, an outer sleeve which is a force fit within a hang-off sub of the drill string and an annular roller bearing unit surrounding the hanger sub and engaging the inner surface of the outer sleeve. The roller bearing unit comprises a plurality of tapered roller bearings having inclined axes of rotation. Such an arrangement is advantageous as it provides the required rotational isolation without the survey instrument assembly being subjected to substantial axial movement or torsion in operation. |
