Patent ID: 7002484

Claim:
A method for surveying a borehole, the method comprising: (a) providing a downhole tool including first and second gravity measurement devices disposed at corresponding first and second positions in the borehole, the first and second gravity measurement devices being constrained from rotating with respect to one another about a substantially cylindrical borehole axis, the tool further including a supplemental reference measurement device disposed at the first position; (b) determining a reference borehole azimuth at the first position using the supplemental reference measurement device; (c) determining a change in borehole azimuth between the first and second positions using the first and second gravity measurement devices; (d) determining borehole azimuth at the second position by applying the change in borehole azimuth determined in (c) to the reference borehole azimuth determined in (b); and (e) repeating (a) through (d) to determine borehole azimuth at multiple selected locations in the borehole, wherein at least one contiguous pair of said multiple selected locations are selected to be a predetermined borehole distance apart, said predetermined borehole distance exceeding twice the borehole distance between the first position and the second position.