Abstract: An electrical circuit board is supported within a tube by means of an aluminum support spine of semicircular section. The circuit board is mounted on the flat surface of the spine with a continuous layer of vibration-absorbing material between the circuit board and the spine. On the opposite side of the circuit board are a number of regularly spaced aluminum posts capped with rubber bumpers for engaging the inside surface of the tube. In order to hold the assembly within the tube and to absorb shocks, two rubber tubular members are disposed in grooves in the spine parallel to the longitudinal axis. The assembly may be introduced into the tube with the tubular members in a relatively contracted state and may subsequently be held firmly in position within the tube with the tubular members in a relatively expanded state.

Abstract: A down-hole signal generator for a mud-pulse telemetry system comprises an annular impeller surrounding a casing and arranged to be driven by the mud passing along the drill string. The impeller serves to drive a torque control arrangement, and preferably also an electrical generator, within the casing. The torque control arrangement is switchable between two states by a signalling actuator in response to an electrical input signal. In a first state the impeller may be driven relatively easily so that it is rotated at a relatively fast speed by the mud flow, whereas, in a second state, a greater torque is required to drive the impeller so that it is rotated at a relatively slow speed. Thus suitable variation of the input signal may be used to vary the impeller speed to transmit a modulated pressure signal in the mud flow which may be sensed at the surface.

Abstract: A housing defines a chamber having a spherical inside surface, and a spherical float is supported within the chamber by a liquid so that the outside surface of the float is equidistantly spaced from the top and bottom of the inside surface of the chamber. The float incorporates a permanent magnet defining diametrically-opposed opposite poles which serve to orient the float with respect to the earth's magnetic field. The liquid is magnetizable, and the float is laterally centered within the chamber by magnetic interaction between the magnet poles and the magnetizable liquid. A differential fluxgate sensing head serves to sense the relative orientation of the housing and the float in a horizontal plane and to supply an electrical output signal indicative of that orientation. A highly accurate direction-finding device is thereby produced at modest cost.

Abstract: A down-hole signal generator for a mud-pulse telemetry system comprises a flow constrictor defining a throttle orifice for the mud passing along a drill string, a throttling member displaceable with respect to a casing to modulate the mud pressure for the purpose of transmitting measurement data up the drill string, and a turbogenerator incorporating an electrical generator within the casing. The flow constrictor and casing form an integrated unit which is installed within a drill collar and is retrievable by drawing it up the inside of the drill string. The throttling member is displaced by a pump according to the torque required to drive the rotor of the generator which is dependent on the electrical load of the generator. The pump incorporates a rotary valve member which supplies the output of the pump to one or other side of a double-acting ram according as to whether the valve member is rotating with a first phase of rotation or a second phase of rotation.

Abstract: A down-hole signal transmitter for a mud pulse telemetry system comprises a flow constrictor defining a throttle orifice for the mud flow, a throttling member displaceable to vary the throughflow cross-section of the throttle orifice, and a pump for displacing the throttling member against the mud flow in order to modulate the mud flow. The displacement of the throttling member is controlled by a hydraulic amplifier, comprising a main pressure relief valve and a subsidiary control valve, and a solenoid to which the output signal of a measuring instrument is supplied. When the main valve is close, the pump displaces a ram, coupled to the throttling member, upwardly.

Abstract: A borehole is surveyed by positioning at the mouth of the borehole a survey instrument having a casing and a three-axis rate gyroscope unit mounted within the casing, and sensing at least two components of gravity in at least two mutually transverse directions with respect to the survey instrument by means of a gravity sensor unit. The survey instrument is then moved along the borehole with the start and finish of the run being at the mouth of the borehole or at some known reference along the path of the borehole. During the run the rates of rotation about three non-coplanar axes are sensed at a series of locations along the length of the borehole by means of the rate gyroscope unit.

Abstract: When surveying a borehole using an instrument responsive to the earth's magnetic field, the assumption is made that the error vector which comprises the difference between the true earth's magnetic field and the measured magnetic field in the borehole is in the direction of the borehole axis. The magnitude of this error vector is determined and used to correct the magnetically measured azimuth.

Abstract: An instrument for measuring the direction of a borehole in order to carry out a spatial survey thereof comprises a gyro-stabilized single-axis platform having its axis coincident with the axis of the borehole and three gravity sensors for measuring three components of gravity in the direction of the borehole axis and in two mutually perpendicular directions in a plane perpendicular to said axis.