Summary

The Method of Moments was originally developed in the 1960s for electrical engineering applications, as described in Roger Harrington's famous book "Field Computation by Moment Methods". The concept was quickly adopted by the mineral exploration community to model the electromagnetic response of volcanogenic massive sulfide deposits as thin conductive sheets, and the technique still forms the basis of many airborne electromagnetic interpretation packages. Targets are parameterized as specific geometric shapes and represented as a distribution of secondary sources whose moments are determined through the solution to a dense matrix equation describing field interactions within the system. The approach is closely related to integral equation modelling but the dimensionality of most problems is reduced by considering objects and shapes of infinitesimal thickness (like thin conductive sheets, plates or tubes). One advantage of the Method of Moments is its ability to describe highly conductive targets as is the situation for steel infrastructure problems, and algorithms can be custom built for rapid calculations. In this workshop we describe our experiences with this technique in the context of steel well casings and applied electromagnetic methods. Our presentation will outline the basic theory of the approach, describe the steps we have taken to validate the method against quasi-analytical and finite-element solutions and finally, give several illustrative examples showing the behavior of single casings, interactions between two casings and demonstrating the capability of modeling more realistic multi-casing scenarios.

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