Patent ID: 7725263
Filing Date: 2010-05-25
Classification: E21B

Abstract:
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.