Downhole calibration system for directional sensors

1. A method of calibrating a directional sensor array, including a plurality of field sensors, located within a drillstring within a wellbore, comprising the steps of:

measuring at least on field with said sensor array at at least four tool face orientations at a survey point in said wellbore; and

utilizing said field measurements to recalibrate a relative scale-factor between cross-axial sensors in said sensor array, wherein said field sensors comprise accelerometers.

2. The method of claim 1 wherein said field comprises a gravitational field.

3. The method of claim 1 wherein said field sensors comprise magnetometers and accelerometers.

4. The method of claim 3 wherein said field comprises a magnetic field and a gravitational field.

5. A method of calibrating a magnetometer sensor array located within a drillstring within a wellbore, comprising the steps of:

measuring a magnetic field with said sensor array at at least four tool face orientations at a survey point in said wellbore; and

utilizing said magnetic field measurements and a measure of gravitational field to recalibrate a relative scale-factor between cross-axial magnetometers in said sensor array.

6. The method of claim 5 further comprising utilizing said field measurements to recalibrate biases in the cross-axial magnetometers.

7. The method of claim 5 further comprising utilizing said field measurements to recalibrate a misalignment between the cross-axial magnetometers.

8. The method of claim 5 further comprising utilizing said field measurements to recalibrate biases in the cross-axial magnetometers and a misalignment between the cross-axial magnetometers.

9. A method of calibrating a magnetometer sensor array located within a drillstring within a wellbore, comprising the steps of:

measuring a magnetic field with said sensor array at at least four tool face orientations at a survey point in said wellbore;

utilizing said field measurements to recalibrate a relative scale-factor between cross-axial magnetometers in said sensor array;

utilizing said field measurements to recalibrate biases in the cross-axial magnetometers and a misalignment between the cross-axial magnetometers; and

combining the corrections of cross-axial magnetic field measurements using said recalibrated relative scale factor and said recalibrated biases and said recalibrated misalignment to determine an axial magnetic field component.

10. A method of calibrating an accelerometer sensor array located within a drillstring within a wellbore, comprising the steps of:

measuring a gravitational field with said sensor array at at least four tool face orientations at a survey point in said wellbore; and

utilizing said gravitational field measurements to recalibrate a relative scale-factor between cross-axial accelerometers in said sensor array.

11. The method of claim 10 further comprising utilizing said field measurements to recalibrate biases in the cross-axial accelerometers.

12. The method of claim 10 further comprising utilizing said field measurements to recalibrate a misalignment between the cross-axial accelerometers.

13. The method of claim 10 further comprising utilizing said field measurements to recalibrate biases in the cross-axial accelerometers and a misalignment between the cross-axial accelerometers.

14. The method of claim 13 further comprising combining the corrections of cross-axial gravitational field measurements using said recalibrated relative scale factor and said recalibrated biases and said recalibrated misalignment to determine an axial gravitational field component.

15. A method of surveying a wellbore utilizing a sensor array located within a drillstring within said wellbore, said method comprising:

obtaining a reference value for a magnitude of earth's magnetic field and a reference value for a magnetic dip angle of the earth's magnetic field;

measuring magnetic and gravitational fields with said sensor array at a plurality of tool face orientations at a survey point in the wellbore;

utilizing said measurements of the magnetic and gravitational fields and said reference values of the magnitude and magnetic dip angle of the earth's magnetic field

to obtain a measurement of an axial component of the earth's magnetic field,

to recalibrate a common scale factor parameter in cross-axial magnetometers in said array;

applying the one or more calibration parameters to the magnetic measurements at said survey point to obtain corrected magnetic field measurements; and

utilizing said gravitational field measurements and said corrected magnetic field measurements to obtain at least one wellbore orientation parameter at said survey point.

16. The method of claim 15 further comprising utilizing said measurements of the magnetic field to recalibrate biases in the cross-axial magnetometers.

17. The method of claim 15 further comprising utilizing said measurements of the magnetic field to recalibrate a misalignment in the cross-axial magnetometers.

18. The method of claim 15 further comprising utilizing said measurements of the magnetic field to recalibrate a relative scale factor in the cross-axial magnetometers.

19. The method of claim 15 further comprising utilizing said measurements of the magnetic field to recalibrate biases and relative scale factor and misalignment in the cross-axial magnetometers.

20. A method of calibrating a directional sensor array located within a drillstring within a wellbore, comprising:

obtaining a reference value for the magnitude of the earth's magnetic field and a reference value for the magnetic dip angle of the earth's magnetic field;

measuring said magnetic and gravitational fields with said sensor array at four or more tool face orientations at a survey point in the wellbore;

utilizing said measurements of the magnetic and gravitational fields and said reference values of the magnitude and magnetic dip of the earth's magnetic field

to obtain a measurement of axial component of the earth's magnetic field, and

to recalibrate cross-axial magnetometers in said array to a calibration parameter comprising a common scale-factor parameter, and

to recalibrate an axial magnetometer in said array to either a bias calibration parameter or a scale factor calibration parameter; and

applying the one or more calibration parameters to the magnetic measurements at one or more survey points to obtain the corrected magnetic field measurements.

21. The method of claim 20 further comprising utilizing said measurements from the magnetic field to recalibrate at least one additional calibration parameter from a group comprising biases of the cross-axial magnetometers and a relative scale factor and a misalignment between the cross-axial magnetometers.

22. A method of calibrating a directional sensor array located within a drillstring within a drill string within a wellbore, the method comprising:

measuring a magnetic field with said sensor array at four or more tool face orientations at a first survey point in the wellbore;

utilizing said measurements of the magnetic field

to recalibrate cross-axial magnetometers in said array to a calibration parameter comprising a relative scale-factor and to at least one additional calibration parameter comprising biases of said cross-axial magnetometers and misalignment between said cross-axial magnetometers and

applying said one or more calibration parameters to the magnetic measurements made at said first survey point or to measurements made at additional survey points to obtain corrected magnetic field measurements.

23. A method of calibrating a directional sensor array located within a drillstring within a drillstring within a wellbore, the method comprising:

obtaining a reference value for magnitude of earth's magnetic field and a reference value for the magnetic dip angle of the earth's magnetic field for the site of said wellbore;

measuring magnetic and gravitational fields with said sensor array at one or more tool face orientations at a survey point within the wellbore;

utilizing said measurements of the magnetic and gravitational fields and said reference values to recalibrate a scale factor calibration parameter in cross-axial magnetometers;

and to recalibrate either a bias or scale factor calibration parameters in a axial magnetometer within said array; and

applying the calibration parameters to the magnetic measurements made at said survey point or made at other survey points to obtain the corrected magnetic field measurements.

24. A method of surveying a wellbore utilizing a sensor array located within a drillstring within said wellbore, the method comprising:

obtaining a reference value for the magnitude of earth's gravitational field and a reference value for the magnetic dip angle of earth's magnetic field;

measuring the magnetic and gravitational fields with said sensor array at four or more tool face orientations at a survey point in the wellbore;

utilizing said measurements of the magnetic and gravitational fields and said reference values of the magnitude of the earth's gravitational field and the magnetic dip of the earth's magnetic field

to obtain a measurement of the axial component of the earth's gravitational field, and

to recalibrate a common scale factor calibration parameter in cross-axial accelerometers in said array, and to

to obtain at least one calibration parameter from a group of calibration parameters comprising

a relative scale-factor in the cross-axial accelerometers,

a misalignment between the cross-axial accelerometers, and

biased in the cross-axial accelerometers;

applying the one or more calibration parameters to the gravitational measurements at said survey point to obtain corrected gravitational field measurements; and

utilizing said corrected gravitational field measurements to obtain at least one well orientation parameter at said survey point.

25. A method of calibrating a directional sensor array located within a drillstring within a wellbore, the method comprising:

obtaining a reference value for the magnitude of earth's gravitational field and a reference value for magnetic dip angle of earth's magnetic field for the site of said wellbore;

measuring the magnetic and gravitational fields with said sensor array at four or more tool face orientations at a survey point in the wellbore;

utilizing said measurements of the magnetic and gravitational fields and said reference values of the magnitude of the earth's gravitational field and the magnetic dip of the earth's magnetic field

to obtain a measurement of an axial component of the earth's gravitational field,

to recalibrate cross-axial gravitational in said array to a calibration parameter comprising a common scale-factor parameter and to at least one additional calibration parameter from a group comprising biases of said cross-axial gravitational and a misalignment and a relative scale factor between said cross-axial gravitational, and

to recalibrate an axial gravitational in said array to either a bias calibration parameter or a scale factor calibration parameter; and

applying the one or more calibration parameters to the gravitational measurements made at said survey point or made at other survey points within said wellbore to obtain the corrected gravitational field measurements.

26. A method of calibrating a directional sensor array located within a drillstring within a wellbore, the method comprising:

measuring gravitational field with said sensor array at four or more tool face orientations at a first survey point in the wellbore;

utilizing said measurements of the gravitational field in combination a with measurement of magnetic field to recalibrate a relative scale-factor calibration parameter between cross-axial accelerometers within said array and at least one additional calibration parameter from a group comprising the biases in the cross-axial accelerometers and the misalignment between the cross-axial accelerometers; and

applying the one or more calibration parameters to the gravitational measurements made at said first survey point or at additional survey points to obtain the corrected gravitational field measurements.

27. A method of calibrating a directional sensor array located within a drillstring within a wellbore, the method comprising:

obtaining a reference value for the magnitude of earth's gravitational field and a reference value for magnetic dip angle of the earth's magnetic field;

measuring magnetic and gravitational fields with said sensor array at one or more tool face orientations at a first survey point in the wellbore;

utilizing said measurements of the magnetic and gravitational fields and said reference values of the magnitude of the earth's gravitational field and the magnetic dip of the earth's magnetic field to recalibrate a scale factor calibration parameter in cross-axial accelerometers within said array;

utilizing said measurements of the magnetic and gravitational fields and said reference values of the magnitude of the earth's gravitational field and the magnetic dip of the earth's magnetic field to determine either a bias calibration parameter or scale factor in an axial accelerometer of said array; and

applying the calibration parameters to the gravitational measurements at said first survey point or at other survey points to obtain the corrected gravitational field measurements.

28. A method of surveying a wellbore utilizing a sensor array located within a drillstring within said wellbore, the method comprising:

obtaining a reference value for the magnitude of earth's magnetic field, a reference value for magnetic dip angle of the earth's magnetic field, and a reference value of magnitude of the earth's gravitational field;

measuring the magnetic and gravitational fields with said sensor array at four or more tool face orientations at a survey point in the wellbore;

utilizing said measurements of the gravitational fields and said reference value of the magnitude of the earth's gravitational field to obtain at least one recalibrate parameter selected from a group parameters comprising

the biases and scale-factors in cross-axial accelerometers within said array,

a misalignment between the cross-axial accelerometers, and

either a bias or scale factor in an axial accelerometer within said array;

applying the at least one recalibrate parameter to the gravitational measurements at said first survey point to obtain corrected gravitational field measurements;

utilizing said measurements of the magnetic field and the corrected gravitational field and said reference values of the magnitude and magnetic dip of the earth's magnetic field to obtain a measurement of axial component of the earth's magnetic field and to recalibrate a common scale-factor parameter in cross-axial magnetometers within said array and to obtain at least one parameter from a group of parameters comprising

the biases and a relative scale-factor in the cross-axial magnetometers,

a misalignment between the cross-axial magnetometers,

applying said one or more recalibrate parameters to the magnetic measurements at said survey point to obtain corrected magnetic field measurements; and

combining said corrected gravitational field measurements and said corrected magnetic field measurements to obtain at least one well orientation parameter at said survey point.

29. A method of surveying a wellbore utilizing a sensor array located within a drillstring within said wellbore, the method comprising:

obtaining a reference value for magnitude of the earth's magnetic field, a reference value for magnetic dip angle of the earth's magnetic field, and a reference value of magnitude of the earth's gravitational field;

measuring the magnetic and gravitational fields with said sensor array at four or more tool face orientations at a survey point in the wellbore;

utilizing said measurements of the magnetic fields and said reference value of the magnitude of the earth's magnetic field to recalibrate at least one parameter selected from a group of parameters comprising

biases and scale-factors in cross-axial magnetometers within said array,

a misalignment between the cross-axial magnetometers, and

either a bias or scale factor in an axial magnetometer;

applying said one or more parameters to the magnetic measurements at said survey point to obtain corrected magnetic field measurements;

utilizing said measurements of the gravitational field and the corrected magnetic field and said reference values of the magnitude of the earth's gravitational field and the magnetic dip of the earth's magnetic field to obtain a measurement of axial component of the earth's gravitational field and to recalibrate a common scale-factor in cross-axial accelerometers within said array and to recalibrate at least one parameter selected from a group of parameters comprising

the biases and a relative scale-factor the cross-axial accelerometers within said array,

a misalignment between the cross-axial accelerometers;

applying the one or more recalibrate parameters to the gravitational measurements at said survey point to obtain corrected gravitational field measurements; and

utilizing said corrected gravitational field measurements and said corrected magnetic field measurements to obtain at least one well orientation measurement at said survey point.