Method of correcting axial and transverse error components in magnetometer readings during wellbore survey operations
First Claim
Patent Images
1. A method of surveying in a wellbore, comprising the method steps of:
- (a) providing a drillstring;
(b) providing a sensor array including magnetic field sensors and gravitational field sensors;
(c) locating said sensor array within said drillstring;
(d) locating said drillstring in said wellbore;
(e) utilizing said drillstring to extend said wellbore;
(f) at a number of survey stations within said wellbore, utilizing said sensor array to make measurements of (a) three components of gravitational field, and (b) three components of magnetic field, with each of said three components of magnetic field possibly including a magnetic field bias error component;
(g) communicating said measurements to a processor which is programmed to execute a set of program instructions, including;
(i) instruction means for selecting for said number of survey stations within said wellbore, an initial estimate for said magnetic field bias error component for particular ones of said three components of magnetic field;
(ii) instruction means for computing, for each survey station within said wellbore, corrected values for said three components of magnetic field utilizing said initial estimate for said magnetic field bias error component for particular ones of said three components of magnetic field;
(iii) instruction means for computing, for each survey station within said wellbore a corrected magnetic field vector utilizing said corrected values for said three components of magnetic field;
(iv) instruction means for computing an improved estimate for said magnetic field bias error component for particular ones of said three components of magnetic field;
(h) establishing a preselected convergence criterion for said corrected magnetic field vector;
(i) iteratively executing said set of program instructions in order to generate, for each survey station within said wellbore, a corrected magnetic field vector which satisfies said preselected convergence criterion and which minimizes the variance of said corrected magnetic field vector with respect to a predetermined value; and
thereby(j) providing substantially corrected magnetic field measurements for each survey station within said wellbore.
0 Assignments
0 Petitions
Accused Products
Abstract
The present invention is directed to a method for compensating V2 for bias error on one or more magnetometers used for one or more borehole directional surveys, comprising determining the constant or first-order varying bias values which minimize the variance of computed local magnetic field vectors with respect to central values, which may be either independent estimates of the local magnetic field vector or the mean values of the computed local magnetic field vectors.
29 Citations
21 Claims
-
1. A method of surveying in a wellbore, comprising the method steps of:
-
(a) providing a drillstring; (b) providing a sensor array including magnetic field sensors and gravitational field sensors; (c) locating said sensor array within said drillstring; (d) locating said drillstring in said wellbore; (e) utilizing said drillstring to extend said wellbore; (f) at a number of survey stations within said wellbore, utilizing said sensor array to make measurements of (a) three components of gravitational field, and (b) three components of magnetic field, with each of said three components of magnetic field possibly including a magnetic field bias error component; (g) communicating said measurements to a processor which is programmed to execute a set of program instructions, including; (i) instruction means for selecting for said number of survey stations within said wellbore, an initial estimate for said magnetic field bias error component for particular ones of said three components of magnetic field; (ii) instruction means for computing, for each survey station within said wellbore, corrected values for said three components of magnetic field utilizing said initial estimate for said magnetic field bias error component for particular ones of said three components of magnetic field; (iii) instruction means for computing, for each survey station within said wellbore a corrected magnetic field vector utilizing said corrected values for said three components of magnetic field; (iv) instruction means for computing an improved estimate for said magnetic field bias error component for particular ones of said three components of magnetic field; (h) establishing a preselected convergence criterion for said corrected magnetic field vector; (i) iteratively executing said set of program instructions in order to generate, for each survey station within said wellbore, a corrected magnetic field vector which satisfies said preselected convergence criterion and which minimizes the variance of said corrected magnetic field vector with respect to a predetermined value; and
thereby(j) providing substantially corrected magnetic field measurements for each survey station within said wellbore. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
-
-
11. A method for determining bias errors affecting magnetometers used in borehole surveying, comprising the steps of:
-
a) measuring three components of the gravitational field and three components of the local magnetic field at a number of survey stations; b) selecting initial estimates for said bias errors; c) computing corrected magnetic field components by use of said estimated bias errors; d) using said corrected magnetic field components to compute a corrected magnetic field vector for each of said survey stations; e) computing improved estimates of said magnetometer bias errors which minimize variance of said magnetic vectors with respect to a central value; and f) iteratively repeating steps c) through e) using said improved estimates, until a defined convergence criterion is met. - View Dependent Claims (12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
-
Specification