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Abstract

An azimuthally tunable resistivity measurement tool is provided. In one embodiment, the tool comprises a set of three skewed receiver antennas and a transmitter antenna. The three skewed receiver antennas are oriented in equally-spaced azimuthal directions to give them preferential sensitivity in those directions. The transmitter antenna transmits a radio-frequency signal that propagates through the formation surrounding a borehole. The signals from the three receiver antennas can be measured and combined to synthesize the signal that would be received by a virtual antenna oriented in any desired direction. Accordingly, virtual receivers oriented perpendicular to the tool axis and with variable azimuthal orientations can be synthesized. The orientation of such a virtual receiver that has a maximized receive signal amplitude can be used to identify the direction of a nearby bed boundary, and the maximized amplitude can be used to estimate the distance to the boundary. In another embodiment, the tool comprises a set of three skewed transmitter antennas and a receiver antenna. The signal responses of the receiver antenna to each of the transmitter antennas can be measured and combined to synthesize a signal response to a virtual transmitter antenna oriented in any desired direction. In yet another embodiment, the tool comprises a set of skewed transmitter antennas and a set of skewed receiver antennas. The skewed transmitter and receiver antennas work cooperatively to establish virtual transmitter/receiver pairs oriented in any desired azimuthal directions.

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First Claim