Measurement-while-drilling assembly using gyroscopic devices and methods of bias removal

• US 6,347,282 B2
• Filed: 12/03/1998
• Issued: 02/12/2002
• Est. Priority Date: 12/04/1997
• Status: Expired due to Term

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Noy, Koen Antonie, Estes, Robert A., Kahn, Jon B.
• Primary Examiner(s): McElheny, Jr., Donald E.
• Application Number:
  US09/204,908
• Publication Number:
  US 20010041963A1
• Time in Patent Office: 1,167 Days
• Field of Search: 702/6, 702/9, 702/10, 324/338-343, 333/02, 333/03, 333/04, 333/10, 333/12, 333/13, 175/45
• 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 using a sensor assembly including a two-axis gyroscope rotatably mounted in a measurement-while-drilling (“

MWD”

) tool in a bottomhole assembly having a drillbit thereon during the drilling of a borehole, the method comprising;

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

(b) taking a measurement from the two-axis gyroscope and at least one additional sensor on the sensor assembly at a first rotational position of the sensor at the first predetermined depth;

(c) rotating the sensor assembly a predetermined angle relative to the first position about a known axis of the sensor to at least one additional rotational position at the predetermined depth and taking a measurement from the two-axis gyroscope and the at least one additional sensor at the at least one additional position;

(d) using a processor on the tool for combining measurements made by the two-axis gyroscope and the at least one additional sensor at the first and at least one additional rotational position to determine a bias in the measurements in at least one of (i) the two-axis gyroscope, and, (ii) the at least one additional sensor, and obtaining corrected measurements therefrom; and

(e) determining from said corrected measurements a parameter of interest 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.

2. The method of claim 1 wherein the at least one additional sensor is selected from the group consisting of:

(A) an accelerometer, and, (B) a magnetometer, and (C) a gyroscope.

3. The method of claim 2, wherein at least one additional sensor comprises a magnetometer and the parameter of interest further comprises magnetic declination at the borehole.

4. The method of claim 1 further comprising taking measurements with the two-axis gyroscope and the at least one additional sensor at a second predetermined depth, obtaining corrected measurements therefrom, and monitoring changes in the parameter of interest.

5. The method of claim 1 wherein the first rotational position corresponds to a peak output value of the two-axis gyroscope.

6. The method of claim 1 wherein the at least one additional rotational position further comprises at least two additional positions and the combining of the measurements further comprises fitting a sinusoid to the measurements.

7. The method of claim 1 wherein the at least one additional 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.

8. The method of claim 1 rotating the sensor assembly further comprises using a stepping motor.

9. The method of claim 1 wherein the at least one additional 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.

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

(a) a housing;

(b) sensor assembly including a two-axis gyroscope and at least one additional sensor rotatably mounted in the housing for providing signals relating to the motion of the tool;

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

(d) a processor in the tool, said processor combining signals from the sensor assembly taken at positions corresponding to a plurality of rotational positions at a predetermined depth in the borehole to determine a bias present in the measurements made by the sensor assembly during drilling of the borehole and determining therefrom corrected measurements, the processor further using said corrected measurements to determine a parameter of interest 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.

11. The MWD assembly of claim 10 wherein the at least one additional sensor is selected from the group consisting of (A) an accelerometer, and (B) a magnetometer.

12. The MWD assembly of claim 10 wherein the processor further corrects measurements from the sensor assembly taken at a borehole depth at other than the predetermined depth to monitor changes in the parameter of interest.

13. The MWD assembly of claim 10 wherein at least one of the plurality of rotational positions corresponds to a peak value of a measurement from the sensor assembly.

14. The MWD assembly of claim 10 wherein the at least one additional 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.

15. The MWD assembly of claim 10 wherein the at least one additional sensor is selected from the group consisting of (i) a magnetometer, and, (ii) an accelerometer.

16. The MWD assembly of claim 15 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.

17. The MWD assembly of claim 16, 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.

18. The MWD assembly of claim 10 further comprising a stepping motor for rotating the sensor assembly.

19. The MWD assembly of claim 10 wherein the two-axis gyroscope has an axis of rotation parallel to an axis of the assembly and the at least one additional sensor comprises an additional two-axis gyroscope with its axis of rotation orthogonal to the axis of rotation of the first gyroscope.

20. The MWD assembly of claim 19 further comprising a first stepping motor for rotating the two-axis gyroscope and a second stepping motor for rotating the additional two-axis gyroscope.

21. The MWD assembly of claim 19 further comprising a single stepping motor for simultaneously rotating the two axis gyroscope and the additional two-axis gyroscope.

22. A method of making measurements using a sensor assembly including a gyroscope rotatably mounted in a measurement-while-drilling (“

MWD”

) tool in a bottomhole assembly having a drillbit thereon during the drilling of a borehole, the method comprising;

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

(b) taking a measurement from the gyroscope and at least one additional sensor on the sensor assembly at a first rotational position of the sensor at the first predetermined depth;

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

(d) using a processor on the tool for combining measurements made by the gyroscope and the at least one additional sensor at the first and the at least one additional rotational position to determine a bias in the measurements in at least one of (i) the gyroscope, and, (ii) the at least one additional sensor, and obtaining corrected measurements therefrom.

23. The method of claim 22 wherein the gyroscope is a two-axis gyroscope.

24. The method of claim 23 further comprising determining from said corrected measurements a parameter of interest 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.

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

MWD”

) tool in a bottomhole assembly having a drillbit thereon during the drilling of a borehole, the method comprising;

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

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

(c) using a stepper motor to rotate the at least one sensor a predetermined angle relative to the first rotational position about a known axis of the sensor to at least one additional rotational position at the predetermined depth and taking a measurement from the at least one sensor at the at least one additional rotational position; and

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

26. The method of claim 25, further comprising correcting at least one of the first and one additional measurements utilizing the determined bias.

27. The method of claim 25 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.

28. The method of claim 26 further comprising determining a parameter of interest utilizing the corrected measurement.

29. The method of claim 28, 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.

30. The method of claim 25 wherein the first position corresponds to a peak output value of the at least one sensor.

31. The method of claim 25 wherein the at least one additional position further comprises at least two additional positions and the combining of the measurements further comprises fitting a sinusoid to the measurements.

32. The method of claim 25 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.