Dictionary:Microlog

A type of microresistivity log using three button electrodes spaced in a vertical line one inch apart located on a pad which is pressed against the borehole wall. The lower electrode is the ‘‘A’’ current electrode. The potential of the upper electrode with respect to a reference electrode on the surface gives a 2-in. micro-normal and the difference between the two upper electrodes gives a 1 1/2-in. microinverse (lateral-type measurement). Because the mud cake usually has appreciably smaller resistivity than the formation, the microinverse reads less than the micronormal when mud cake is present; this difference (called separation) indicates a permeable formation. Similar to the contact log or Minilog. Microlog is a Schlumberger tradename. See Figure M-10.