Abstract: This invention relates to a composite torque shaft for connecting a downhole fluid motor to the drill bit at the end of a drill string. The composite torque shaft comprises an elongate matrix body with oriented fibers fixed therein. The fibers are particularly oriented to provide the composite torque shaft with significant torque strength and stiffness while allowing bending flexibility. Accordingly, the composite torque shaft converts the gyrating and rotating motion of the rotor in the fluid motor to the pure rotation of the drill bit.

Abstract: The present invention provides a preperforated casing for a well bore and a method of installing a preperforated casing in a well bore. The inventive casing comprises (a) a conduit having a plurality of apertures extending through the wall thereof and (b) a liner fixed adjacent at least a portion of the interior surface of the conduit such that the liner is positioned adjacent the apertures and is operable for preventing fluid flow through the apertures. The liner is removable from the conduit by drilling. Additionally, the liner comprises a material which, upon drilling, will break up into pieces which can be readily circulated out of the well. The inventive method comprises the steps of running the inventive casing into a well bore and then drilling the liner such that the liner is broken up into pieces and the above-mentioned apertures are open for fluid flow.

Abstract: A chemically removable casing section is spotted in a casing string opposite a formation through which a horizontal borehole is to be drilled. The casing section is selectively dissolved by a chemical solution, and a horizontal borehole is drilled into the formation through the window in the casing string.

Abstract: A method and apparatus for measuring casing wall thickness using an axial main coil for generating a flux field enveloping the casing wall, and sensing actual field distribution by means of plural radial sensing coils each disposed at a radial position within the casing thereby to derive data sufficient to model a reference calibration for good casing wall structure; and, sensing flux leakage from the casing wall to detect anomalies of wall structure relative to the established reference calibration for output indication versus position along the casing.