Question

modern resistivity logging tools are two types: laterolog and induction.

Differentiate between them?

Answer 1

Induction tools are conductivity-sensitive devices, which are most accurate in low- to medium-resistivity formations. Laterolog tools are resistivity devices, which are most accurate in medium- to high-resistivity formations

  

Laterologs work best in saltier muds or in normal muds in high resistivity formations. They will not work in air filled or cased holes

The laterolog is a direct current (DC) tool based on Ohm's Law. The tools have been designed to produce reliable resistivity measurements in boreholes containing highly saline drilling fluids and/or when surrounded by highly resistive rocks. The logging current is prevented from flowing up and down within the drilling fluid by placing focusing electrodes (A1 and A2) on both sides of a central measure electrode A0, as illustrated below. The focusing electrodes force measure current to flow only in the lateral direction, perpendicular to the axis of the logging device.

Conventional induction logs measure conductivity perpendicular to the axis of the tool. In a vertical well, this is the horizontal direction. Vertical conductivity may be quite different. Recent developments have introduced a log that can measure vertically as well as horizontally. It is in the commercialization phase of development, and promises to be very useful in thin bedded and dipping reservoir rocks.

The tool works in air, oil, or mud filled open holes but salt muds give poor results, although the array induction can handle saltier muds than earlier versions of the tool. It does not work in cased holes. A cased hole formation resistivity log is available