Patent ID: 6882937
Filing Date: 2005-04-19
Classification: E21B

Abstract:
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) determining local azimuths at three or more sites in the previously surveyed section of the borehole using the first and second gravity measurement devices; (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 historic survey.