Gyro-stabilized single-axis platform

• US 4,071,959 A
• Filed: 03/23/1976
• Issued: 02/07/1978
• Est. Priority Date: 03/25/1975
• Status: Expired due to Term

• Current Assignee: Baroid Technology Incorporated (Halliburton Company)
• Original Assignee: Sperry-Sun Incorporated
• Inventors: Russell, Michael K., Russell, Anthony W.
• Primary Examiner(s): Stephan, Steven L.
• Application Number:
  US05/669,518
• Time in Patent Office: 686 Days
• Field of Search: 33/304, 33/312, 33/313, 33/318
• US Class Current: 33/312
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism

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.

Claims

1. An instrument for measuring the direction of a borehole comprising a case having a longitudinal axis coincident, in use, with the axis of the borehole, a single-degree-of-freedom gyro comprising an outer gimbal mounted in the case with its axis coincident with the longitudinal axis thereof, an inner gimbal mounted in the outer gimbal with its axis coincident with the outer gimbal axis, a gyro rotor mounted in the inner gimbal, means for sensing angular movement of the inner gimbal relative to the outer gimbal and applying a torque to the outer gimbal to rotate it about its axis so that the inner gimbal precesses back to its initial position, means for measuring the angle of rotation of the case about its longitudinal axis relative to the outer gimbal and a gravity sensor unit for measuring three components of gravity in three non-coplanar directions.

2. An instrument according to claim 1, in which the gravity sensors are mounted on the outer gimbal.

3. An instrument according to claim 1, in which the gravity sensors are mounted on the case of the instrument.

4. An instrument according to claim 3, including a resolver mounted on the instrument case and having its rotor connected to the outer gimbal, two of the gravity sensors being arranged to sense components of gravity in directions perpendicular to the longitudinal axis of the instrument and having their outputs connected to the inputs of the resolver.

5. A method of surveying a borehole comprising:

moving a survey instrument along the borehole, said survey instrument comprising a case having a longitudinal axis coincident, in use, with the axis of the borehole, a single-degree-of-freedom gyro comprising an outer gimbal mounted in the case with its axis coincident with the longitudinal axis thereof, an inner gimbal mounted in the outer gimbal with its axis perpendicular to the outer gimbal axis, a gyro rotor mounted in the inner gimbal;

continually sensing angular movement of the inner gimbal relative to the outer gimbal as the instrument moves along the borehole and applying a torque to the outer gimbal to rotate it about its axis so that the inner gimbal precesses back to its initial position;

determining at each of a series of survey stations spaced along the borehole a set of three components of gravity in three non-coplanar directions relative to the outer gimbal;

calculating, from the sensed components of gravity at each of said survey stations, the inclination of the borehole and the non-rotative high-side angle of the instrument relative to a reference direction which does not rotate about the longitudinal axis of the instrument as it travels along the borehole at each station; and

calculating, from said inclination and non-rotative high-side angle, the azimuth of the borehole at each station.

6. A method of surveying a borehole according to claim 5, wherein the set of three components of gravity is measured, at each station, by three sensors mounted on the outer gimbal.

7. A method of surveying a borehole according to claim 5, wherein a second set of three components of gravity is measured, at each station, by three sensors mounted on the instrument case, the method further comprising measuring, at each station, the angle of rotation of the instrument case relative to the outer gimbal and calculating said first mentioned set of components of gravity from said second set and said angle of rotation.

8. A method of surveying a borehole according to claim 7, wherein one component of each of said sets of components of gravity is parallel to the outer gimbal axis and the other two components of the first-mentioned set are calculated by setting the stator and rotor of a resolver at a relative angle equal to said angle of rotation and applying the other two components of the second set to the input of the resolver.