Resistivity: Electrode Devices and How They Evolved

We have seen the utility of knowing formation resistivity and an idealized approach to making the measurement. This chapter focuses on the evolution of one type of electrical logging tool: electrode devices, so named because the measurement elements are simply metallic electrodes. These devices utilize low-frequency current sources, in most cases below 1,000 Hz. The historical progression from the normal device to traditional focused dual laterologs will be traced. An indication of the measurement limitations for each of these types of tools will be given and related to their design. The methods used for the prediction and interpretation of their response will be discussed.