Micro-Lateral Logging

Basic Information

Description

Micro-lateral logging is a type of lateral logging. In saline-mud drilling holes, the mud cake is thin, so conventional micro-electrode devices have poor contact with the borehole wall; the increasing influence of the mud degrades the curve’s ability to reflect resistivity variations in the flushed and invaded zones. To address this, an electrode assembly is used in which an annular guard electrode of the same polarity as the main electrode is added to the micro-electrode pad.

The logging method employing this electrode assembly is called micro-lateral logging. During operation, the main current I₀ is focused by the guard current I_p into a cylindrical bundle that enters the formation vertically. I₀ is kept constant, while I_p is automatically adjusted so that the monitor electrodes M₁ and M₂ remain equipotential at all times. By continuously measuring the potential U at electrode M₁ or M₂, a micro-lateral logging curve reflecting the resistivity variation of the flushed zone is obtained. Some micro-lateral tools use only one guard ring electrode without monitor electrodes; their principle is the same as that of lateral logging.

It is currently widely used in coalfield, coal-bed methane (CBM), shale gas, hydrology, and radioactive uranium deposits, and is one of the mandatory measurement parameters for CBM and shale gas.

Specification