MEASUREMENT-WHILE-DRILLING ASSEMBLY USING GYROSCOPIC DEVICES AND METHODS OF BIAS REMOVAL

• US 20010041963A1
• Filed: 12/03/1998
• Published: 11/15/2001
• Est. Priority Date: 12/04/1997
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: KAHN, JON B., ESTES, ROBERT ALAN, NOY, KOEN A.
• Granted Patent: US 6,347,282 B2
• Time in Patent Office: Days
• US Class Current: 702/6
• CPC Class Codes: E21B 47/022 of the borehole, e.g. using geomagnetism
• CPC Class Codes: G01C 19/38 with north-seeking action by other than magnetic means, e.g. gyrocompasses using earth's rotation

Abstract

This invention provides a measurement-while-drilling (MWD) downhole assembly for use in drilling boreholes which utilizes gyroscopes, magnetometers and accelerometers for determining the borehole inclination and azimuth during the drilling of the borehole. The downhole assembly includes at least one gyroscope that is rotatably mounted in a tool housing to provide signals relating to the earth'"'"'s rotation. A device in the tool can rotate the gyroscope and other sensors on the tool at any desired degree. A processor in the tool combines measurements from the sensors taken at a plurality of positions at the same depth to determine the systematic bias in the sensors before further processing. Accelerometers in the MWD tool provide gravity measurements from which the toolface and inclination are determined. The unbiased gyroscopic measurements are used in conjunction with the tool face and inclination measurements to determine the azimuth and tool face with respect to true north. Three axially spaced apart magnetometers may be used to correct for local magnetic disturbances. Additionally, when measurements are made with magnetic, accelerometer and gyroscopic measurements along three different axes, the unbiased measurements may be combined to provide an improved determination of the tool orientation.

Claims

1. A method of making measurements made by at least one sensor rotatably mounted in a measurement-while-drilling (“

MWD”

) tool during the drilling of a borehole, the method comprising;

(a) locating the MWD tool in the borehole at a predetermined depth;

(b) taking a measurement from the at least one sensor at a first position of the sensor at the predetermined depth;

(c) rotating the at least one sensor a predetermined angle relative to the first position about a known axis of the sensor to at least a second position at the predetermined depth and taking a measurement from the at least one sensor at the at least second position; and

(d) combining the first measurement and the at least second measurement to determine a bias in the measurements made by the at least one sensor.

2. The method of

claim 1

, further comprising correcting at least one of the first and second measurements utilizing the determined bias.

3. The method of

claim 1

wherein the at least one sensor is selected from the group consisting of:

(i) an accelerometer, (ii) a magnetometer, and (iii) a two-axis gyroscope.

4. The method of

claim 2

further comprising determining a parameter of interest utilizing the corrected measurement.

5. The method of

claim 4

, wherein the at least one sensor is a two-axis gyroscope and the parameter of interest is selected from the group consisting of (i) an azimuth with respect to the true north, (ii) toolface orientation with respect to the true north, iii) amplitude of measurements of the earth'"'"'s rate vector for a two-axis gyroscope, (iv) amplitude of measurements of the earth'"'"'s rate vector for a three-axis gyroscope, and (v) local apparent latitude for a three-axis gyroscope.

6. The method of

claim 4

wherein the at least one sensor is a two-axis gyroscope, the method further comprising correcting measurements of the gyroscope taken at a borehole depth at other than the predetermined depth to monitor changes in the parameter of interest.

7. The method of

claim 1

wherein the first position corresponds to a peak output value of the at least one sensor.

8. The method of

claim 1

wherein the at least second position further comprises at least two positions and the combining of the measurements further comprises fitting a sinusoid to the measurements.

9. The method of

claim 1

wherein the at least one sensor further comprises three three-axis magnetic sensors spaced axially apart on the MWD tool, the method further comprising determining a position and strength of a local magnetic disturbance.

10. The method of

claim 1

wherein the at least one sensor further comprises a magnetometer, a gyroscope, and an accelerometer, the method further comprising determining a parameter of interest utilizing the measurements made by the magnetometer, gyroscope and accelerometer, wherein at least one of said measurements has been corrected utilizing the determined bias.

11. The method of

claim 10

, wherein the parameter of interest is selected from a group consisting of (i) an azimuth with respect to the true north, (ii) toolface orientation with respect to the true north, iii) amplitude of measurements of the earth'"'"'s rate vector for a two-axis gyroscope, (iv) amplitude of measurements of the earth'"'"'s rate vector for a three-axis gyroscope, (v) local apparent latitude for a three-axis gyroscope, and, (vi) magnetic declination at the borehole.

12. The method of

claim 1

wherein the rotation of the at least one sensor is accomplished by using a stepping motor.

13. The method of

claim 1

wherein the at least one sensor further comprises three three-axis magnetic sensors spaced axially apart on the MWD tool, the method further comprising determining a position where a gradient of the magnetic field is substantially zero.

14. A measurement-while-drilling (MWD) downhole assembly for use in drilling boreholes, comprising:

(a) a housing;

(b) at least one sensor rotatably mounted in the housing, said at least one sensor providing signals relating to the motion of the tool;

(c) a device in the tool for rotating the at least one sensor about an axis of the at least one sensor; and

(d) a processor in the tool, said processor combining signals from the at least one sensor taken at positions corresponding to a plurality of rotational positions at the same depth in the borehole to determine a bias present in the measurements made by the at least one sensor during drilling of the borehole.

15. The MWD assembly of

claim 14

wherein the processor corrects at least one measurement made by the at least one sensor using the determined bias.

16. The MWD assembly of

claim 14

wherein the at least one sensor is selected from the group consisting of (i) an accelerometer, (ii) a magnetometer, and (iii) a gyroscope.

17. The MWD assembly of

claim 15

wherein the processor further determines a parameter of interest utilizing the corrected measurement.

18. The MWD assembly of

claim 15

, wherein the at least one sensor is a gyroscope and the parameter of interest is selected from a group consisting of (i) an azimuth with respect to the true north, (ii) toolface orientation with respect to the true north, iii) amplitude of measurements of the earth'"'"'s rate vector for a two-axis gyroscope, (iv) amplitude of measurements of the earth'"'"'s rate vector for a three-axis gyroscope, and (v) local apparent latitude for a three-axis gyroscope.

19. The MWD assembly of

claim 15

wherein the processor further corrects measurements of the gyroscope taken at a borehole depth at other than the predetermined depth to monitor changes in the parameter of interest.

20. The MWD assembly of

claim 15

wherein at least one of the plurality of rotational positions corresponds to a peak output value of the at least one sensor.

21. The MWD assembly of

claim 14

wherein the at least one sensor further comprises three magnetic sensors spaced apart axially on the MWD tool, the processor further combining signals from the three magnetic sensors to determine a position and strength of a local magnetic disturbance.

22. The MWD assembly of

claim 14

wherein the at least one sensor further comprises a gyroscope and at least one additional sensor selected from the group consisting of (i) a magnetometer, and, (ii) an accelerometer.

23. The MWD assembly of

claim 22

the processor further determining a parameter of interest utilizing a measurement from the gyroscope corrected for said bias, and a measurement from the at least one additional sensor.

24. The MWD assembly of

claim 23

, wherein the parameter of interest is selected from a group consisting of (i) an azimuth with respect to the true north, (ii) toolface orientation with respect to the true north, iii) amplitude of measurements of the earth'"'"'s rate vector for a two-axis gyroscope, (iv) amplitude of measurements of the earth'"'"'s rate vector for a three-axis gyroscope, and (v) local apparent latitude for a three-axis gyroscope, and, (vi) magnetic declination at the borehole

25. The MWD assembly of

claim 14

further comprising a stepping motor for rotating the at least one sensor.

26. The MWD assembly of

claim 14

wherein the at least one sensor comprises a first two-axis gyroscope with its axis of rotation parallel to an axis of the assembly and a second two-axis gyroscope with its axis of rotation orthogonal to the axis of rotation of the first gyroscope.

27. The MWD assembly of

claim 26

further comprising a first stepping motor for rotating the first gyroscope and a second stepping motor for rotating the second gyroscope.

28. The MWD assembly of

claim 26

further comprising a single stepping motor for simultaneously rotating the first gyroscope and the second gyroscope.