Patent ID: 8141635
Filing Date: 2012-03-27
Classification: E21B

Abstract:
1. A system for determining orientation of a measurement tool in a cased borehole comprising: a tool housing forming part of the measurement tool and being designed to be deployed in a cased section of a borehole; a volume within the tool housing and containing a reference fluid having a first density; a marker having a second density, the marker being disposed within the volume containing reference fluid such that the marker is moveable within the volume, the second density being substantially different from the first density; a sensing system adapted and positioned to sense the position of the marker within volume containing the reference fluid; and a processing system adapted and programmed to determine orientation information of the measurement tool based at least in part on combining information relating to the position of the marker with prior recorded data representing orientation measurements made while the section of the borehole was not yet cased.