Advanced Technology For Mapping Subsurface Water Conductivity

Abstract

Advanced Technology for Mapping Subsurface Water Conductivity is a threeyear research program which was funded by the Department of Energy in October 2000. Its objective is to combine Magnetometric Resistivity (MMR) surface magnetic field measurements with Electrical Resistivity Tomography (ERT) borehole potential measurements to calculate subsurface conductivity. The data sets measured by ERT and MMR will be input to a combined ERT/MMR inversion code for the purpose of calculating the subsurface conductivity distribution with increased resolution. This paper presents the results of the work performed during the first year of this project. MMR instrumentation was developed to spatially resolve the surface magnetic field associated with an induced subsurface alternating current low between borehole ERT electrode pairs. It consists of a variable frequency alternating current source and a synchronously detected, spatially resolved vector B-field measurement system. MMR data preprocessing algorithms are complete and include the removal of magnetic fields associated with the surface conductors delivering current to the subsurface structure. A three-dimensional Finite Difference Time Domain forward model that calculates electrical and magnetic fields based on current flow through a medium characterized by conductivity, permeability, and permittivity was also developed. Initial tests have been conducted in the Mud Lake, Idaho sediment beds.