On Feasibility of Inductive Conductivity Measurement of Formation Surrounding a Metal Casing

Bypassing hydrocarbon-layers when casing the borehole can result in recovering of only small part of estimated original oil in place. The inductive measurement of subsurface rocks (formation) conductivity through casing is required in order to successfully reevaluate existing wells and detect bypassed oil. The main problem in the cased- hole inductive measurement is strong signal attenuation and high variations in the properties of the steel casing. In this study, we investigate the feasibility of the inductive measurement in the presence of steel casings with realistic electromagnetic properties. We discuss the method for cancellation of the casing effect and inadequacy of the casing factor for the same purpose. We analyze effects of the excitation frequency and mutual separation of a transmitter-receiver coil pair on the expected measurement sensitivity.