Calibration correction method for magnetic survey tools
First Claim
1. A method for determining the orientation of the axis of a borehole with respect to an Earth-fixed reference coordinate system at a selected series of locations in the borehole, the borehole having a trajectory, and adapted to receive a drill string, comprising the steps of:
- a) defining a model for the influence of magnetic interference from elements of the drill string on the measurement of components of the Earth'"'"'s magnetic field in the borehole in terms of an unknown vector, a measurement vector, and a measurement matrix relating the unknown vector and the measurement vector,b) measuring at two or more selected locations along the borehole trajectory;
1) at least one of;
i) two cross-borehole components of the Earth'"'"'s gravity field at said selected locations in the borehole, andii) two cross-borehole components and an along-borehole component of the Earth'"'"'s gravity field at said selected locations in the borehole;
2) two cross-borehole components of the Earth'"'"'s magnetic field and an along-borehole component of the Earth'"'"'s magnetic field at said selected locations;
c) computing the elements of said measurement vector and said measurement matrix from said measured Earth'"'"'s gravity and Earth'"'"'s magnetic field components for said selected locations;
d) solving for said unknown vector using said measurement vector and said measurement matrix,e) computing for each of said selected locations corrected values for the Earth'"'"'s magnetic field components using said unknown vector, said model, and said measured Earth'"'"'s magnetic field components,f) and determining a value for the azimuthal orientation of said borehole axis at each said selected locations using said corrected values for the Earth'"'"'s magnetic field components and said measured gravity components.
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Abstract
A method for determining the orientation of the axis of a borehole with respect to an Earth-fixed reference coordinate system at a selected series of locations in the borehole, the borehole having a trajectory, and adapted to receive a drill string, comprising defining a model for the influence of magnetic interference from elements of the drill string on the measurement of components of the Earth'"'"'s magnetic field in the borehole in terms of an unknown vector, a measurement vector, and a measurement matrix relating the unknown vector and the measurement vector; measuring at two or more selected locations along the borehole trajectory at least one of two cross-borehole components of the Earth'"'"'s gravity field at the selected locations in the borehole, and two cross-borehole components and an along-borehole component of the Earth'"'"'s gravity field at the selected locations in the borehole; two cross-borehole components and an along-borehole component of the Earth'"'"'s magnetic field at the selected locations; computing the elements of the measurement vector and measurement matrix from the measured Earth'"'"'s gravity and magnetic field components for the selected locations; solving for the unknown vector; computing corrected values for the Earth'"'"'s magnetic field components using the unknown vector, the model, and the measured Earth'"'"'s magnetic field components; and determining a value for the azimuthal orientation of the borehole axis using the corrected values for the Earth'"'"'s magnetic field components and the measured gravity components.
61 Citations
22 Claims
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1. A method for determining the orientation of the axis of a borehole with respect to an Earth-fixed reference coordinate system at a selected series of locations in the borehole, the borehole having a trajectory, and adapted to receive a drill string, comprising the steps of:
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a) defining a model for the influence of magnetic interference from elements of the drill string on the measurement of components of the Earth'"'"'s magnetic field in the borehole in terms of an unknown vector, a measurement vector, and a measurement matrix relating the unknown vector and the measurement vector, b) measuring at two or more selected locations along the borehole trajectory; 1) at least one of; i) two cross-borehole components of the Earth'"'"'s gravity field at said selected locations in the borehole, and ii) two cross-borehole components and an along-borehole component of the Earth'"'"'s gravity field at said selected locations in the borehole; 2) two cross-borehole components of the Earth'"'"'s magnetic field and an along-borehole component of the Earth'"'"'s magnetic field at said selected locations; c) computing the elements of said measurement vector and said measurement matrix from said measured Earth'"'"'s gravity and Earth'"'"'s magnetic field components for said selected locations; d) solving for said unknown vector using said measurement vector and said measurement matrix, e) computing for each of said selected locations corrected values for the Earth'"'"'s magnetic field components using said unknown vector, said model, and said measured Earth'"'"'s magnetic field components, f) and determining a value for the azimuthal orientation of said borehole axis at each said selected locations using said corrected values for the Earth'"'"'s magnetic field components and said measured gravity components. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18)
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19. The method of determining the orientation of the axis of a borehole in the Earth, that includes
a) determining a set of along-axis magnetometer errors at different points along the borehole, b) determining a model composed of a fixed magnetic component and an induced magnetic component, associated with magnetization in the borehole, c) and fitting said errors to said model for determining bias and scale factors, d) whereby accurate, along-axis measurements can be computed using the determined bias and scale factor values.
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20. The method of claim i including employing magnetometers to effect said b) 2) step measuring, wherein said along-borehole component is represented by:
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space="preserve" listing-type="equation">(1+K.sub.I)*H.sub.z +H.sub.Fwherein the quantity (1+KI) is the scale factor of the measurement and the quantity HF is a bias type of correction, and said method steps, including said measurements at said two or more locations, derive values for (1+KI) and HF. - View Dependent Claims (21, 22)
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Specification