Real-time casing detection using tilted and crossed antenna measurement

摘要

Methods and apparatus for detecting nearby conductors such as pipes, well casing, etc., from within a borehole. A nearby casing string can be detected by transmitting an electromagnetic signal from a transmit antenna on a downhole logging tool and measuring a parallel response signal with a first receive antenna parallel to the transmit antenna and a perpendicular response signal with a second receive antenna perpendicular to the transmit antenna, both receive antennas on the downhole logging tool. As the tool rotates, the transmitting and measuring are repeated to determine the azimuthal dependence of the parallel and perpendicular response signals. The azimuthal dependence is analyzed to determine a diagonal component of said azimuthal dependence for each response signal. Distance to a casing string can be estimated using the diagonal component of each response signal. At least one of the antennas is preferably tilted.

主权项

1. A method for detecting a conductive feature from within a borehole, the method comprising:
transmitting an electromagnetic signal from a transmit antenna on a drilling collar or a downhole logging tool; measuring a parallel response signal with a first receive antenna parallel to the transmit antenna and a perpendicular response signal with a second receive antenna perpendicular to the transmit antenna, both receive antennas on the drilling collar or the downhole logging tool; repeating said transmitting and measuring to obtain an azimuthal dependence of said parallel response signal and said perpendicular response signal; determining a diagonal component of said azimuthal dependence for each response signal; and estimating a distance to a casing string using the diagonal component of each response signal.