| 摘要 |
The apparatus includes an annular current electrode (Ao) mounted on a body and guard electrodes (A2, A'2) disposed on the body above and below the annular current electrode. A first measurement current (Io) is emitted by the central current electrode (Ao) and focusing currents are emitted by the guard electrodes (A2, A'2). A first output signal representative of the deep resistivity of the formations is generated in response to the first measurement current (Io). One of the guard electrodes (A2) includes two longitudinally spaced-apart portions, and an array of azimuthal current electrodes (Aazii) that are circumferentially spaced-apart from one another is disposed between these two portions. Second measurement currents (Aazi) emitted by the azimuthal current electrodes (Aazi) are focused longitudinally by the currents emitted by the said two portions of the guard electrode (A2). Second output signals are generated in response to the second measurement current (Iazi), which output signals are representative of the resistivity of the formations in a plurality of directions around the borehole. A high resolution resistivity signal is calculated as a function of the mean of the second measurement currents (Iazi).
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