Abstract: The disclosure is directed to an apparatus and method for determining dielectric constant and/or conductivity of earth formations surrounding a borehole. Electromagnetic energy is generated at a first location in the borehole. The relative attenuation of the electromagnetic energy is detected at a second location in the borehole. The detection is preferably performed using a first or "close" differential receiver arrangement. The relative phase of the electromagnetic energy is detected at a third location in the borehole, the third location being spaced farther from the first location than is the second location; in other words, the second location is between the first and third locations. The relative phase shift of the electromagnetic energy is measured by a second or "far" differential receiver arrangement located at the third location in the borehole.

Abstract: In accordance with an illustrative embodiment of the present invention, a well logging apparatus uses a narrow wall-engaging pad equipped with an array of vertical electrodes. The length of these electrodes is greater near the edges of the pad than in the middle thereof. Circuits are connected to the electrodes for propagating a focused current primarily through the zone of the adjacent formation likely to be flushed by the borehole fluid. This current and the associated potential difference are measured to produce a signal representative of the resistivity of the flushed zone.