Gravity zaimuth measurement at a non-rotting housing
First Claim
1. A method for surveying a subterranean borehole, the method comprising:
- (a) providing a string of downhole tools including first and second gravity measurement devices at corresponding first and second longitudinal positions in the borehole, the first and second gravity measurement devices being substantially free to rotate with respect to one another about a substantially cylindrical borehole axis, the string of tools further including an angular position sensor disposed to measure a relative angular position between the first and second gravity measurement devices;
(b) causing the first and second gravity measurement devices to measure corresponding first and second gravity vector sets;
(c) causing the angular position sensor to measure a corresponding relative angular position between the first and second gravity measurement devices; and
(d) processing the first and second gravity vector sets and the angular position to calculate a change in borehole azimuth between the first and second positions in the borehole.
3 Assignments
0 Petitions
Accused Products
Abstract
Aspects of this invention include methods for surveying a subterranean borehole. In one exemplary aspect, a change in borehole azimuth between first and second longitudinally spaced gravity measurement sensors may be determined directly from gravity measurements made by the sensors and a measured angular position between the sensors. The gravity measurement sensors are typically disposed to rotate freely with respect to one another about a longitudinal axis of the borehole. Gravity MWD measurements in accordance with the present invention may be advantageously made without imposing any relative rotational constraints on first and second gravity sensor sets. The present invention also advantageously provides for downhole processing of the change in azimuth between the first and second gravity sensor sets. As such, Gravity MWD measurements in accordance with this invention may be advantageously utilized in closed-loop steering control methods.
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Citations
26 Claims
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1. A method for surveying a subterranean borehole, the method comprising:
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(a) providing a string of downhole tools including first and second gravity measurement devices at corresponding first and second longitudinal positions in the borehole, the first and second gravity measurement devices being substantially free to rotate with respect to one another about a substantially cylindrical borehole axis, the string of tools further including an angular position sensor disposed to measure a relative angular position between the first and second gravity measurement devices; (b) causing the first and second gravity measurement devices to measure corresponding first and second gravity vector sets; (c) causing the angular position sensor to measure a corresponding relative angular position between the first and second gravity measurement devices; and (d) processing the first and second gravity vector sets and the angular position to calculate a change in borehole azimuth between the first and second positions in the borehole. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for surveying a subterranean borehole, the method comprising:
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(a) providing first and second gravity measurement devices at corresponding first and second longitudinal positions in the borehole; (b) causing the first and second gravity measurement devices to measure corresponding first and second gravity vector sets; and (c) processing downhole the first and second gravity vector sets to calculate a change in borehole azimuth between the first and second positions in the borehole. - View Dependent Claims (15, 16)
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17. A closed-loop method for controlling the direction of drilling of a subterranean borehole, the method comprising:
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(a) providing a string of downhole tools including first and second gravity measurement devices at corresponding first and second longitudinal positions in the borehole, the first and second gravity measurement devices being substantially free to rotate with respect to one another about a substantially cylindrical borehole axis, the string of tools further including an angular position sensor disposed to measure a relative angular position between the first and second gravity measurement devices; (b) causing the first and second gravity measurement devices to measure corresponding first and second gravity vector sets; (c) causing the angular position sensor to measure a corresponding relative angular position between the first and second gravity measurement devices; and (d) processing the first and second gravity vector sets and the angular position to control the direction of drilling of the subterranean borehole. - View Dependent Claims (18, 19, 20, 21, 22)
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23. A system for providing near-bit surveying measurement of a subterranean borehole while drilling, the system comprising:
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a measurement while drilling sub including a first gravity measurement sensor set, the measurement while drilling sub disposed to be coupled with a drill string; a steering tool including a housing deployed about a shaft, the shaft disposed to be coupled with the drill string, the housing and the shaft substantially free to rotate with respect to one another, the steering tool further including an angular position sensor disposed to measure the relative angular position between the housing and the shaft, the housing including a second gravity measurement sensor set; a downhole controller disposed to; (a) cause the first and second gravity measurement sensor sets to measure corresponding first and second gravity vector sets; (b) cause the angular position sensor to measure a corresponding relative angular position between the housing and the shaft; and (c) process the first and second gravity vector sets and the angular position to calculate a change in borehole azimuth between the first and second sensor sets. - View Dependent Claims (24, 25, 26)
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Specification