microspherical log

1. n. [Formation Evaluation]
An electrode device with small spacings from which the current flow, and hence the measurement, is focused a short distance into the formation. The microspherical log measures the resistivity of the flushed zone with minimum influence from the mudcake or the undisturbed zone. The principle of spherical focusing is used. The electrodes are mounted on a pad that is pressed against the borehole wall. In a typical tool design, 90% of the signal comes from within 3 in. [7.6 cm] of the pad, ensuring that the undisturbed zone rarely has an effect.