Other

Nl Sperry Sun, Inc.

Smart Stabilizer Systems Limited

Nl Industries

Anthony W Russell

Michael King Russell

The invention relates to a method and an apparatus for use in surveying boreholes. The method of the invention comprises the following steps: providing an instrument package in a leading end of a drillstring, the instrument package comprising first and second single-axis sensors mounted for rotation with the drillstring about the rotational axis of the drillstring, the first sensor being an accelerometer and the second sensor being a magnetic fluxgate or a rate gyro; rotating the drillstring; deriving from the first sensor the inclination angle of the drillstring at the instrument package; and deriving from the second sensor the azimuth angle of the drillstring at the instrument package.

Borehole surveying

A borehole drilling and survey assembly includes a drill string of magnetic material, a non-magnetic drill collar, and a non-magnetic rotary drilling system including a drill bit. A near-bit survey instrument is located in the rotary drilling system at a fixed distance from the junction of the drill string and the drill collar. A second survey instrument is located in the drill collar at a fixed distance from said junction. The survey instruments measure the local values of the component of the earth's magnetic along the borehole axis, and these values are processed to remove the magnetic effects of the drillstring. The survey instruments optionally also measure gravity vector components to enable borehole heading to be derived.

Surveying of boreholes

Borehole surveying methods and apparatus for surveying the true longitudinal magnetic field within a substantially non-magnetic drill collar. A plurality of longitudinal magnetic field measurements are made to provide a longitudinal-position-dependent series of magnetic field measurements BZ(z) which enable the true magnitude of the terrestial magnetic field BZe in the direction of the longitudinal axis of the borehole to be calculated on the basis that BZ(z)=BZe+E(z), where E(z) is the longitudinal-position-dependent longitudinal magnetic field error induced by the magnetism of the drill string and the bottom-hole assembly. Several different methods of calculation are described, including polar and non-polar magnetic error function models. The methods can be extended to a full survey of the borehole heading by contemporaneous measurements of two further magnetic fields in each of two mutually orthogonal axes each also orthogonal to the longitudinal axis, along with contemporaneous gravity vector component measurements in each of these three axes.

Method and apparatus for determining the azimuth of a borehole by

A method of deriving the true magnitude of the terrestial magnetic field in the direction of the longitudinal axis of a borehole at a region of the borehold occupied by an instrumentation package equipped with magnetic vector measuring means for measuring the lateral magnetic vectors Bx and By and further equipped with gravitational vector measuring means for measuring each of the three gravitational vectors Gx, Gy, and Gz. The method comprises the steps of performing said measurements of the magnetic vectors and the gravitational vectors and from said vector measurements solving the equation:

A transmitter comprises an impeller assembly rotatable by a liquid flow, and an electrical generator having a stator and a rotor arranged to be driven by the impeller assembly. The impeller assembly comprises a main impeller portion and a secondary impeller portion angularly displaceable relative to one another about the axis of rotation of the impeller assembly in response to a change in load of the generator so as to vary the pressure drop across the rotating impeller assembly. Thus appropriate variation of the load of the generator may be used to control the impeller assembly in such a manner as to transmit pressure signals within the liquid flow. Such a transmitter is particularly suitable for transmitting measurement data to the surface from a measuring instrument at the end of a drill string within a borehole. Furthermore such a transmitter can be constructed so as to be readily retrievable without requiring withdrawal of the drill string from the borehole.

Signal transmitters

An accelerometer has a moving magnet within a housing. The magnet is mounted within a support member connected to the center of a diaphragm so as to permit movement of the magnet along a measurement axis extending in the axial direction of the support member by deformation of the diaphragm and so as to permit movement of the magnet along two mutually orthogonal measurement axes parallel to the diaphragm by flexing of the diaphragm to allow for pivoting of the support member. Furthermore displacement of the magnet with respect to the three mutually transverse measurement axes in response to an applied force is sensed by a pickoff capacitor, and a respective output signal proportional to the component of the applied force along each of the measurement axes is supplied by associated sensing circuitry. Simultaneously the magnet is restored to its null position by associated force coil pairs. The use of a single magnet for measurement along the three axes renders the accelerometer of high accuracy and decreases the size of the measurement assembly.

Tri-axial accelerometers

For the purposes of determining the orientation of a surveying instrument in a borehole, while compensating for the effects of perturbing magnetic fields associated with magnetized sections of the drill string both above and below the instrument, the inclination angle .theta. and the highside angle .phi. of the instrument are determined, together with two transverse components Bx and By of the local magnetic field as measured at the instrument in the borehole. Additionally either a single component of, or the magnetide of, the true earth's magnetic field at the location of the borehole is ascertained from a look-up table or directly by measurement away from the influence of the drill string. A value .PSI.a for the azimuth angle of the instrument is then determined from the inclination and highside angles, the measured component(s) of the local magnetic field, and only the single component of, or the magnitude of, the true earth's magnetic field.

Method of determining the orientation of a surveying instrument in a

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 the throttle orifice to modulate the mud pressure for the purpose of transmitting measurement data up the drill string, and a turbogenerator. The turbogenerator incorporates an annular impeller surrounding a casing and arranged to be driven by the mud passing along the drill string, and a rotatable magnet assembly disposed in a mud-free environment within the casing. The impeller includes an electrically conductive drive ring and the rotatable magnet assembly includes rare earth magnets, so that, when the impeller is rotated by the mud flow, eddy currents are induced in the drive ring by the magnetic field associated with the magnets and the magnet assembly is caused to rotate with the impeller by virtue of the interaction between the magnetic field associated with the magnets and the magnetic field associated with the induced currents. In this manner torque may be imparted to an electrical generator within the casing without a rotating seal having to be provided between the impeller and the generator.

Mud pressure control system with magnetic torque transfer

An instrument for monitoring the direction of a borehole comprises an elongate casing having its longitudinal axis coincident, in use, with the axis of the borehole, an outer gimbal pivotally mounted within the casing with its pivot axis coincident with the longitudinal axis of the casing, a gyroscope unit mounted in the outer gimbal, a torque motor and a gravity sensor unit. At the beginning of a run the instrument is positioned at the mouth of the borehole. The rate of rotation about an axis transverse to the outer gimbal axis is then sensed by the gyroscope unit, and the outer gimbal is slewed by the torque motor in dependence on the sensed rate so as to align the transverse axis along an East/West direction. The instrument is then moved along the borehole and the rate of rotation about the outer gimbal axis is continually sensed by the gyroscope unit, the outer gimbal being torqued by the motor in dependence on the sensed rate to stabilize the outer gimbal about its axis. Simultaneously the components of gravity are sensed by the gravity sensor unit. The resulting measurements are used to determine the inclination and azimuth at a plurality of points along the length of the borehole.

Instruments for monitoring the direction of a borehole

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.

Apparatus for signalling within a borehole while drilling

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. The phase of rotation is determined by a torque-sensitive actuator coupled to the valve member by a shaft and incorporating an escapement plate tiltable about an axis transverse to the shaft by a torque drive arm for driving the rotor.

Mud pressure control system

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. However, when the signal supplied to the solenoid is such as to magnetically attract an armature, the control valve is opened to conduct a small flow of oil between the pump input and the pump output, and this in turn causes the main valve to open thus conducting a much larger flow of oil from the pump input to the pump output and allowing the throttling member to be displaced downwardly by the pressure of the mud flow. The power required to modulate the mud flow with this arrangement is very low and is easily provided by a down-hole electrical generator.

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. The position of the borehole at each measuring location is then calculated by determining the initial set of direction cosines from the sensed gravity components and an assumed initial value of the azimuth angle and incrementing these values using the rates of rotation sensed by the rate gyroscope unit to obtain the sets of direction cosines at subsequent measuring locations.

Surveying of a borehole for position determination

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.

Growing community of inventors

Cheltenham, United Kingdom

Anthony W Russell