Borehole surveying
First Claim
1. A method of surveying a borehole at a drilling site comprising:
- (a) obtaining local geomagnetic field data by spot measurement of the earth'"'"'s magnetic field at a local measurement site which is sufficiently close to the drilling site that the measurement data is indicative of the earth'"'"'s magnetic field at the drilling site but which is sufficiently remote from the drilling site that the measurement data is unaffected by magnetic interference from the drilling site and other man-made installations;
(b) obtaining time-varying geomagnetic field data by combining said local geomagnetic field data with data indicative of variation of the geomagnetic field with respect to time obtained by monitoring variation of the earth'"'"'s magnetic field with respect to time at a remote monitoring site;
(c) obtaining downhole magnetic field data by monitoring by means of a surveying instrument the magnetic field in the vicinity of the borehole at a series of locations along the borehole; and
(d) determining the orientation of the borehole from said downhole magnetic field data and said time-varying geomagnetic field data.
4 Assignments
0 Petitions
Accused Products
Abstract
A borehole survey is conducted at a drilling site S by a so-called Interpolated In-Field Referencing (IIFR) method in which: (a) absolute local geomagnetic field data is obtained by spot measurement of the earth'"'"'s magnetic field at a local measurement site R which is sufficiently close to the drilling site S that the measurement data is indicative of the earth'"'"'s magnetic field at the drilling site S but which is sufficiently remote from the drilling site S that the measurement data is unaffected by magnetic interference from the drilling site and other man-made installations; (b) time-varying geomagnetic field data is obtained by combining the absolute local geomagnetic field data with data indicative of variation of the geomagnetic field with respect to time obtained by monitoring variation of the earth'"'"'s magnetic field with respect to time at a remote monitoring site P1, P2; (c) downhole magnetic field data is obtained by monitoring by means of a surveying instrument the magnetic field in the vicinity of the borehole at a series of locations along the borehole; and (d) the orientation of the borehole is determined from the downhole magnetic field data and the time-varying geomagnetic field data. Such a survey method takes into account short-term variations in the geomagnetic field caused by electrical currents in the ionosphere and is therefore more accurate than known survey methods.
37 Citations
9 Claims
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1. A method of surveying a borehole at a drilling site comprising:
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(a) obtaining local geomagnetic field data by spot measurement of the earth'"'"'s magnetic field at a local measurement site which is sufficiently close to the drilling site that the measurement data is indicative of the earth'"'"'s magnetic field at the drilling site but which is sufficiently remote from the drilling site that the measurement data is unaffected by magnetic interference from the drilling site and other man-made installations; (b) obtaining time-varying geomagnetic field data by combining said local geomagnetic field data with data indicative of variation of the geomagnetic field with respect to time obtained by monitoring variation of the earth'"'"'s magnetic field with respect to time at a remote monitoring site; (c) obtaining downhole magnetic field data by monitoring by means of a surveying instrument the magnetic field in the vicinity of the borehole at a series of locations along the borehole; and (d) determining the orientation of the borehole from said downhole magnetic field data and said time-varying geomagnetic field data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A system for surveying a borehole at a drilling site comprising:
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(a) a surveying instrument for monitoring the magnetic field in the vicinity of the borehole at a series of locations along the borehole in order to obtain downhole magnetic field data; (b) means for recording local geomagnetic field data obtained by spot measurement of the earth'"'"'s magnetic field at a local measurement site which is sufficiently close to the drilling site that the measurement data is indicative of the earth'"'"'s magnetic field at the drilling site but which is sufficiently remote from the drilling site that the measurement data is unaffected by magnetic interference from the drilling site and other man-made installations; (c) means for determining time-varying geomagnetic field data by combining said local geomagnetic field data with data indicative of variation of the geomagnetic field with respect to time obtained by monitoring variation of the earth'"'"'s magnetic field with respect to time at a remote monitoring site; and (d) means for determining the orientation of the borehole from said downhole magnetic field data and said time-varying geomagnetic field data.
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Specification