Scaled Experimental Verification of Single-Well Induction Conductivity Measurement Through Nonmagnetic Casing

The electromagnetic induction measurement of dimensions, integrity, or material properties of conductive objects is especially challenging in the case when the electrical conductivity of these objects spans five to seven orders of magnitude. Such an application is the conductivity measurement of the surrounding rocks from within a metal casing of an oil well. The rock conductivity measurement is required in order to determine and revaluate hydrocarbon-bearing layers. We present the first experimental verification of the single-well through-casing induction measurement on a scaled laboratory model of a borehole lined with a stainless steel or copper casing surrounded with a low-conductive medium. The measurements are in the frequency range of 2-16 kHz (10-80 Hz in case of the actual borehole). We explain the theoretical background of the method, describe the scaled model and experimental procedure, and discuss the experimental results. The measurement results are in agreement with the theoretical predictions (relative error less than 15%), and the equivalence of the results for the steel and copper casings (average relative discrepancy less than 10%) corroborates that the rock conductivity measurement can be corrected for variations in the casing properties (dimensions, electrical conductivity, and magnetic permeability).