Method to assess uncertainties and correlations resulting from multi-station analysis of survey data
First Claim
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1. A method of a drilling a borehole, comprising:
- obtaining errors associated with multi-station survey measurements obtained at a drill string in the borehole;
partitioning the obtained errors into a set of magnetometer bias errors and a set of measurement errors including scale factor errors;
determining a post-fit covariance matrix for the magnetometer bias errors that includes the effects of the measurement errors on the magnetometer bias errors;
determining an ellipsoid of constant probability for the post-fit covariance matrix, wherein the ellipsoid of constant probability defines an uncertainty in trajectory of the drill string;
comparing the ellipsoid of constant probability for the post-fit covariance matrix to the ellipsoid of constant probability for a standard error model;
when the ellipsoid of constant probability for the post-fit covariance matrix is less than the ellipsoid of constant probability for the standard error model, determining an ellipsoid of constant probability for a target error model based on reducing magnetometer bias errors and scale factor errors of the standard error model, the ellipsoid of constant probability for the target error model being bound by the ellipsoid of constant probability for the post-fit covariance matrix;
correcting a trajectory of the drill string using the target error model; and
steering the drill string in the borehole using the corrected trajectory.
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Abstract
A system, method and computer-readable medium for a drilling a borehole is disclosed. Errors associated with multi-station survey measurements are obtained and partitioned into a set of estimated errors and a set of considered errors. A post-fit covariance matrix is determined from the estimated errors and includes the effects of the considered errors on the estimated errors. A drilling parameter of a drill string in the borehole may be altered using the determined post-fit covariance matrix.
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Citations
28 Claims
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1. A method of a drilling a borehole, comprising:
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obtaining errors associated with multi-station survey measurements obtained at a drill string in the borehole; partitioning the obtained errors into a set of magnetometer bias errors and a set of measurement errors including scale factor errors; determining a post-fit covariance matrix for the magnetometer bias errors that includes the effects of the measurement errors on the magnetometer bias errors; determining an ellipsoid of constant probability for the post-fit covariance matrix, wherein the ellipsoid of constant probability defines an uncertainty in trajectory of the drill string; comparing the ellipsoid of constant probability for the post-fit covariance matrix to the ellipsoid of constant probability for a standard error model; when the ellipsoid of constant probability for the post-fit covariance matrix is less than the ellipsoid of constant probability for the standard error model, determining an ellipsoid of constant probability for a target error model based on reducing magnetometer bias errors and scale factor errors of the standard error model, the ellipsoid of constant probability for the target error model being bound by the ellipsoid of constant probability for the post-fit covariance matrix; correcting a trajectory of the drill string using the target error model; and steering the drill string in the borehole using the corrected trajectory. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A system for drilling a borehole, comprising:
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a drill string configured to drill the borehole; and a processor configured to; obtain errors associated with previous downhole survey measurements, partition the obtained errors into a set of magnetometer bias errors and a set of measurement errors including scale factor errors, determine a post-fit covariance matrix for the magnetometer bias errors that includes the effects of a variation of the measurement errors on a variation of the magnetometer bias errors; determine an ellipsoid of constant probability for the post-fit covariance matrix, wherein the ellipsoid of constant probability defines an uncertainty in trajectory of the drill string; compare the ellipsoid of constant probability for the post-fit covariance matrix to the ellipsoid of constant probability for a standard error model; when the ellipsoid of constant probability for the post-fit covariance matrix is less than the ellipsoid of constant probability for the standard error model, determine an ellipsoid of constant probability for a target error model based on reducing magnetometer bias errors and scale factor errors of the standard error model, the ellipsoid of constant probability for the target error model being bound by the ellipsoid of constant probability for the post-fit covariance matrix; correct a trajectory of the drill string using the target error model; and steer the drill string using the corrected trajectory. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. A non-transitory computer-readable medium having a set of instructions stored thereon and accessible to a processor to perform a method of a drilling a borehole, the method comprising:
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obtaining errors associated with multi-station survey measurements; partitioning the obtained errors into a set of magnetometer bias errors and a set of measurement errors including scale factor errors; determining a post-fit covariance matrix for the magnetometer bias errors that includes the effects of a variation of the measurement errors on a variation of the magnetometer bias errors; determining an ellipsoid of constant probability for the post-fit covariance matrix, wherein the ellipsoid of constant probability defines an uncertainty in trajectory of the drill string; comparing the ellipsoid of constant probability for the post-fit covariance matrix to the ellipsoid of constant probability for a standard error model; when the ellipsoid of constant probability for the post-fit covariance matrix is less than the ellipsoid of constant probability for the standard error model, determining an ellipsoid of constant probability for a target error model based on reducing magnetometer bias errors and scale factor errors of the standard error model, the ellipsoid of constant probability for the target error model being bound by the ellipsoid of constant probability for the post-fit covariance matrix; correcting a trajectory of the drill string using the target error model; and steering the drill string in the borehole based on the corrected trajectory. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28)
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Specification