Downhole referencing techniques in borehole surveying
First Claim
1. A method for determining rotational offset between first and second gravity measurement devices, the first and second gravity measurement devices disposed at corresponding first and second positions on a downhole tool deployed in a borehole, the method comprising:
- (a) positioning the tool in a previously surveyed section of borehole, the previously surveyed section providing a historical survey including at least three previously surveyed azimuthal reference points within the previously surveyed section of borehole;
(b) utilizing the first and second gravity measurement devices to determine local azimuths at three or more sites in the previously surveyed section of the borehole;
(c) comparing local azimuths determined in (b) with the historical survey; and
(d) determining a rotational offset between the first and second measurement devices that gives a best fit in (c) between local azimuths determined in (b) and the historical survey.
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Abstract
A method for determining rotational offset between first and second gravity measurement devices deployed on a downhole tool is disclosed. The method includes positioning the tool in a previously surveyed section of a borehole that provides a historical survey including at least three previously surveyed azimuthal reference points and utilizing the gravity measurement devices to determine local azimuths at three or more sites in the previously surveyed section of the borehole. The method further includes comparing local azimuths with the historical survey and determining a rotational offset between the measurement devices that gives a best fit between local azimuths and the historical survey. A system adapted to execute the disclosed method and a computer system including computer-readable logic configured to instruct a processor to execute the disclosed method are also provided.
58 Citations
30 Claims
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1. A method for determining rotational offset between first and second gravity measurement devices, the first and second gravity measurement devices disposed at corresponding first and second positions on a downhole tool deployed in a borehole, the method comprising:
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(a) positioning the tool in a previously surveyed section of borehole, the previously surveyed section providing a historical survey including at least three previously surveyed azimuthal reference points within the previously surveyed section of borehole;
(b) utilizing the first and second gravity measurement devices to determine local azimuths at three or more sites in the previously surveyed section of the borehole;
(c) comparing local azimuths determined in (b) with the historical survey; and
(d) determining a rotational offset between the first and second measurement devices that gives a best fit in (c) between local azimuths determined in (b) and the historical survey. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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24. A method for determining rotational offset between first and second gravity measurement devices, the first and second gravity measurement devices disposed at corresponding first and second positions on a downhole tool deployed in a borehole, the method comprising:
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(a) positioning the tool in a previously surveyed section of borehole, the previously surveyed section providing a historical survey including at least three previously surveyed azimuthal reference points within the previously surveyed section of the borehole;
(b) measuring first and second gravity vector sets at each of five or more sites;
(c) utilizing a projected rotational offset to determine a set of corrected gravity vectors at each of the five or more sites;
(d) replacing one of the gravity vector sets at each of the five or more sites with the corrected gravity vectors at the corresponding sites;
(e) utilizing the corrected gravity vectors to determine the local azimuths at each of the five or more sites;
(f) comparing the local azimuths determined in (e) with the historical survey;
(g) determining a rotational offset between the first and second measurement devices that gives a best fit in (f) between local azimuths determined in (e) and the historical survey.
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25. A method for determining rotational offset between first and second gravity measurement devices, the first and second gravity measurement devices disposed at corresponding first and second positions on a downhole tool deployed in a borehole, the method comprising:
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(a) positioning the tool in a previously surveyed section of borehole, the previously surveyed section providing a historical survey including at least three previously surveyed azimuthal reference points within the previously surveyed section of borehole;
(b) measuring first and second gravity vector sets using the first and second gravity measurement devices;
(c) determining local azimuths using the gravity vectors measured in (b);
(d) repeating (b) and (c) at two or more additional sites in the previously surveyed section of the borehole;
(e) comparing the local azimuths determined in (c) and (d) with the historical survey; and
(f) determining a rotational offset between the first and second measurement devices that gives a best fit in (e) between local azimuths determined in (c) and (d) and the historical survey.
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26. A system for determining rotational offset between first and second gravity measurement devices deployed in a borehole, the system comprising:
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a down hole tool including first and second gravity measurement devices deployed thereon, the tool operable to be positioned in a previously surveyed section of borehole, the previously surveyed section providing a historical survey including at least three previously surveyed azimuthal reference points within the previously surveyed section of borehole; and
a processor configured to determine;
(A) local azimuths at three or more sites in the previously surveyed section of the borehole from readings taken from the first and second gravity measurement devices;
(B) a comparison of local azimuths determined in (A) with the historical survey; and
(C) a rotational offset between the first and second measurement devices that gives a best fit in (B) between local azimuths determined in (A) and the historical survey. - View Dependent Claims (27)
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28. A computer system comprising:
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at least one processor; and
a storage device having computer-readable logic stored therein, the computer-readable logic accessible by and intelligible to the processor;
the processor further disposed to receive input from first and second gravity measurement devices when said first and second measurement devices are deployed at corresponding first and second positions in a borehole, the first and second positions located within a previously surveyed section of borehole;
the processor further having access to a historical survey of the previously surveyed section of borehole, the historical survey including at least three previously surveyed azimuthal reference points within the previously surveyed section of borehole;
the computer-readable logic further configured to instruct the processor to execute a method for determining rotational offset between the first and second gravity measurement devices, the method comprising;
(a) determining local azimuths at three or more sites in the previously surveyed section of borehole using input from the first and second gravity measurement devices;
(b) comparing local azimuths determined in (a) with the historical survey; and
(c) determining a rotational offset between the first and second measurement devices that gives a best fit in (b) between local azimuths determined in (a) and the historical survey. - View Dependent Claims (29, 30)
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Specification