Laterolog

Laterolog is a type of electrical resistivity logging tool used in borehole geophysics to measure formation resistivity. It is commonly employed in oil and gas exploration to help determine lithology, porosity, and hydrocarbon saturation by characterizing how readily rocks conduct electric current.

The tool operates by injecting a controlled electrical current into the surrounding formation through current electrodes located on the tool. Guard or shield electrodes are used to confine the current path and suppress borehole effects, while one or more potential electrodes measure the resulting voltage drop in the adjacent formation. From the measured voltage and the known current, the formation resistivity (Rxo) is inferred. The design aims to concentrate the current into the formation at a specific depth of investigation, minimizing interference from borehole fluid and invaded zones.

Laterolog tools come in several variants that differ in depth of investigation and resolution. Common distinctions include shallow- and deep-penetration configurations, and advancements such as high-definition laterolog (HDL) that improve vertical resolution. The electrode spacing and tool geometry determine the depth range over which resistivity is sensed, producing a set of resistivity curves that complement other logs.

Applications include determining formation resistivity, which, when combined with porosity data, enables estimation of water saturation through Archie's equation. Laterolog data are used to identify hydrocarbons, delineate invaded zones, and aid in reservoir evaluation. Practical use requires corrections for borehole size, mud conductivity, invasion effects, and casing conditions, and results are typically interpreted alongside other logs for robust formation assessment.