1. n. [Formation Evaluation]
A particular combination of a spontaneous potential log and three electrical logs consisting of a 16-in. [40-cm] short normal, a 64-in. [162-cm] long normal and an 18-ft, 8-in. [5.7-m] lateral. With this combination, it is possible to correct for the effects of invasion in many average logging environments. This combination is sometimes called a conventional electrical log or survey, or simply electrical log, and is also referred to as the ES.