Gravity azimuth measurement at a non-rotating housing

• US 7,725,263 B2
• Filed: 05/22/2007
• Issued: 05/25/2010
• Est. Priority Date: 05/22/2007
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Smith International Incorporated (Schlumberger NV)
• Inventors: Sugiura, Junichi
• Primary Examiner(s): TSAI, CAROL S W
• Application Number:
  US11/805,213
• Publication Number:
  US 20080294343A1
• Time in Patent Office: 1,099 Days
• Field of Search: 702/6, 702/9, 166/255.2, 175/26, 175/45, 175/61, 703/9, 333/13, 333/10, 333/08, 333/04, 333/21, 731/524.6, 731/524.5, 731/520.3, 340/853.8, 340/853.1, 340/856.3
• US Class Current: 702/9
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism

Abstract

Aspects of this invention include methods for surveying a subterranean borehole. In one exemplary aspect, a change in borehole azimuth between first and second longitudinally spaced gravity measurement sensors may be determined directly from gravity measurements made by the sensors and a measured angular position between the sensors. The gravity measurement sensors are typically disposed to rotate freely with respect to one another about a longitudinal axis of the borehole. Gravity MWD measurements in accordance with the present invention may be advantageously made without imposing any relative rotational constraints on first and second gravity sensor sets. The present invention also advantageously provides for downhole processing of the change in azimuth between the first and second gravity sensor sets. As such, Gravity MWD measurements in accordance with this invention may be advantageously utilized in closed-loop steering control methods.

Claims

1. A method for surveying a subterranean borehole, the method comprising:

(a) providing a string of downhole tools including first and second gravity measurement devices at corresponding first and second longitudinal positions in the borehole, the first and second gravity measurement devices being substantially free to rotate with respect to one another about a substantially cylindrical borehole axis, the string of tools further including an angular position sensor disposed to measure a relative angular position between the first and second gravity measurement devices;

(b) causing the first and second gravity measurement devices to measure corresponding first and second gravity vector sets;

(c) causing the angular position sensor to measure a corresponding relative angular position between the first and second gravity measurement devices; and

(d) processing the first and second gravity vector sets and the angular position to calculate a change in borehole azimuth between the first and second positions in the borehole.

2. The method of claim 1, wherein the first and second gravity measurement devices each comprise tri-axial accelerometer sets.

3. The method of claim 1, wherein the first gravity measurement device is deployed in a measurement while drilling sub rotationally coupled with a drill string and the second gravity measurement device is deployed in a substantially non-rotating steering tool housing.

4. The method of claim 3, wherein (d) further comprises:

(i) processing at the measurement while drilling sub the first gravity vector set to calculate a borehole inclination and a toolface angle at the first position;

(ii) transmitting the borehole inclination and the toolface angle at the first position from the measurement while drilling sub to the steering tool;

(iii) processing at the steering tool the second gravity vector set to calculate a borehole inclination and a toolface angle at the second position; and

(iv) processing at the steering tool the relative angular position between the first and second gravity measurement devices, the borehole inclination and the toolface angle at the first position, and the borehole inclination and the toolface angle at the second position to calculate the change in borehole azimuth between the first and second gravity measurement devices.

5. The method of claim 3, wherein (d) further comprises:

(i) processing at the steering tool the second gravity vector set to calculate a borehole inclination and a toolface angle at the second position;

(ii) transmitting the borehole inclination and the toolface angle at the second position from the steering tool to the measurement while drilling sub;

(iii) processing at the measurement while drilling sub the first gravity vector set to calculate a borehole inclination and a toolface angle at the first position; and

(iv) processing at the measurement while drilling sub the relative angular position between the first and second gravity measurement devices, the borehole inclination and the toolface angle at the first position, and the borehole inclination and the toolface angle at the second position to calculate the change in borehole azimuth between the first and second gravity measurement devices.

6. The method of claim 1, wherein the first gravity measurement device is deployed above a mud motor and the second gravity measurement device is deployed below the mud motor.

7. The method of claim 1, wherein the angular position sensor comprises:

a plurality of magnets circumferentially spaced about a first downhole tool component, the magnets being rotationally coupled to the first gravity measurement sensor; and

a plurality of magnetic field sensors circumferentially spaced about a second downhole tool component, the magnetic field sensors being rotationally coupled to the second gravity measurement sensor, at least one of the magnetic field sensors being in sensory range of magnetic flux from at least one of the magnets.

8. The method of claim 7, wherein (e) further comprises:

(i) causing each of the magnetic field sensors to measure a magnetic flux; and

(ii) processing the magnetic flux measurements to determine the relative angular position between the first and second gravity measurement sensors.

9. The method of claim 1, wherein (d) further comprises:

(i) processing the relative angular position and the second gravity vector set to calculate a corrected gravity vector set; and

(ii) processing the first gravity vector set and the corrected gravity vector set to calculate a change in borehole azimuth between the first and second positions in the borehole.

10. The method of claim 9, wherein the corrected gravity vector set is calculated in (i) according to the equation:

11. The method of claim 1, wherein (d) further comprises:

(i) processing the first and second gravity vector sets to calculate borehole inclination and toolface angles at the first and second positions in the borehole;

(ii) processing the relative angular position, the borehole inclination at the first and second positions, and the toolface angles at the first and second positions to calculate a change in borehole azimuth between the first and second positions in the borehole.

12. The method of claim 11, wherein the change in azimuth is calculated in (ii) according to the equation:

13. The method of claim 1, wherein (d) further comprises:

(i) processing the first and second gravity vector sets to calculate borehole inclination and toolface angles at the first and second positions in the borehole;

(ii) processing the angular position and the toolface angle at the second position in the borehole to calculate a corrected toolface angle; and

(iii) processing the borehole inclination at the first and second positions, the toolface angle at the first position, and the corrected toolface angle to calculate a change in borehole azimuth between the first and second positions in the borehole.

14. A method for surveying a subterranean borehole, the method comprising:

(a) providing first and second gravity measurement devices at corresponding first and second longitudinal positions in the borehole;

(b) causing the first and second gravity measurement devices to measure corresponding first and second gravity vector sets;

(c) processing downhole the first and second gravity vector sets to calculate borehole inclination and toolface angles at the first and second positions in the borehole; and

(d) processing downhole the borehole inclination and toolface angles at the first and second positions to calculate a change in borehole azimuth between the first and second positions in the borehole, wherein the change of azimuth is calculated according to the equation;

15. A closed-loop method for controlling the direction of drilling of a subterranean borehole, the method comprising:

(a) providing a string of downhole tools including first and second gravity measurement devices at corresponding first and second longitudinal positions in the borehole, the first and second gravity measurement devices being substantially free to rotate with respect to one another about a substantially cylindrical borehole axis, the string of tools further including an angular position sensor disposed to measure a relative angular position between the first and second gravity measurement devices;

(b) causing the first and second gravity measurement devices to measure corresponding first and second gravity vector sets;

(c) causing the angular position sensor to measure a corresponding relative angular position between the first and second gravity measurement devices; and

(d) processing the first and second gravity vector sets and the angular position to control the direction of drilling of the subterranean borehole.

16. The method of claim 15, wherein (d) further comprises:

(i) processing the first and second gravity vector sets and the angular position to determine a borehole inclination and a borehole azimuth at the second position;

(ii) processing the borehole inclination and a borehole azimuth at the second position in combination with a preordained borehole inclination and borehole azimuth to control the direction of drilling of the subterranean borehole.

17. The method of claim 15, wherein (d) further comprises:

(i) processing the first and second gravity vector sets and the angular position to determine a change in borehole inclination and a change in borehole azimuth between the first and second positions;

(ii) processing the change in borehole inclination and the change in borehole azimuth in combination with preordained changes in the borehole inclination and the borehole azimuth to control the direction of drilling of the subterranean borehole.

18. The method of claim 15, wherein the first gravity measurement device is deployed in a measurement while drilling sub rotationally coupled with a drill string and the second gravity measurement device is deployed in a substantially non-rotating steering tool housing, the steering tool housing including at least one blade disposed to extend radially outward from the housing into contact with the borehole wall.

19. The method of claim 18, wherein (d) further comprises processing the first and second gravity vector sets and the angular position to control extension and retraction of the at least one blade.

20. The method of claim 15, wherein the angular position sensor comprises:

a plurality of magnets circumferentially spaced about a first downhole tool component, the magnets being rotationally coupled to the first gravity measurement sensor; and

a plurality of magnetic field sensors circumferentially spaced about a second downhole tool component, the magnetic field sensors being rotationally coupled to the second gravity measurement sensor, at least one of the magnetic field sensors being in sensory range of magnetic flux from at least one of the magnets.

21. A system for providing near-bit surveying measurement of a subterranean borehole while drilling, the system comprising:

a measurement while drilling sub including a first gravity measurement sensor set, the measurement while drilling sub disposed to be coupled with a drill string;

a steering tool including a housing deployed about a shaft, the shaft disposed to be coupled with the drill string, the housing and the shaft substantially free to rotate with respect to one another, the steering tool further including an angular position sensor disposed to measure the relative angular position between the housing and the shaft, the housing including a second gravity measurement sensor set;

a downhole controller disposed to;

(a) cause the first and second gravity measurement sensor sets to measure corresponding first and second gravity vector sets;

(b) cause the angular position sensor to measure a corresponding relative angular position between the housing and the shaft; and

(c) process the first and second gravity vector sets and the angular position to calculate a change in borehole azimuth between the first and second sensor sets.

22. The system of claim 21, wherein the angular position sensor comprises:

a plurality of magnets circumferentially spaced about the shaft, the magnets being rotationally coupled to the first gravity measurement sensor; and

a plurality of magnetic field sensors circumferentially spaced about the housing, the magnetic field sensors being rotationally coupled to the second gravity measurement sensor, at least one of the magnetic field sensors being in sensory range of magnetic flux from at least one of the magnets.

23. The method of claim 21, wherein the change in borehole azimuth is calculated in (c) according to the equation:

24. The method of claim 21, wherein the controller is further disposed to:

(d) process the change in borehole azimuth calculated in (c) to control extension and retraction of the at least one blade deployed in the steering tool housing.