Complex Formation Resistivity - The Forgotten Half Of The Resistivity Log Available to Purchase

Log analysts have recently become reacquainted with the fact that formation resistivity is actually a complex quantity. It has a reactive as well as a resistive component, both of which vary with frequency. The phenomenon has been known and exploited in metal mining exploration for many years. It is commonly referred to as "induced polarization" or IP and more recently as "complex resistivity". The reactive component of the complex formation resistivity is affected by the rocks' cation exchange capacity as well as by the presence of disseminate metallic conductors. Thus, measurements of complex formation resistivity bears importantly on the estimation of shaliness. Instrumentation for the measurement of the complex formation resistivity in a borehole is discussed. Pulse transient methods are contrasted with the so-called "frequency domain" method and the advantages and disadvantages of each technique are reviewed. Examples of IP logs in two drill hole environments, the shaley sand sedimentary environment, and the disseminated sulfide environment will be shown. Methods for the incorporation of the complex formation resistivity with other log measurements for improving estimates of formation factor are presented. Measurement of complex formation resistivity is a logical and important improvement to a valuable wireline logging measurement which historically provided the foundation for Formation Evaluation. It promises to become an important measurement for estimating, in situ, the parameter of cation exchange capacity or Qv.