| 摘要 |
Aspects of this invention include methods for surveying a subterranean bo rehole. In one exemplary aspect, a change in borehole azimuth between first and second longitudinally spaced gravity measurement sensors may be determin ed directly from gravity measurements made by the sensors and a measured ang ular position between the sensors. The gravity measurement sensors are typic ally disposed to rotate freely with respect to one another about a longitudi nal axis of the borehole. Gravity MWD measurements in accordance with the pr esent invention may be advantageously made without imposing any relative rot ational constraints on first and second gravity sensor sets. The present inv ention 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 uti lized in closed-loop steering control methods.
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