Electrical resistance tomography using steel cased boreholes as long electrodes

摘要

Electrical resistance tomography (ERT) using multiple electrodes installed in211u001eboreholes has been shown to be useful for both site characterization and process 211u001emonitoring. In some cases, however, installing multiple downhole electrodes is 211u001etoo costly (e.g., deep targets) or risky (e.g., contaminated sites). For these 211u001ecases we have examined the possibility of using the steel casings of existing 211u001eboreholes as electrodes. Several possibilities can be considered. The first case 211u001ewe investigated uses an array of steel casings as electrodes. This results in 211u001every few data and thus requires additional constraints to limit the domain of 211u001epossible inverse solutions. Simulations indicate that the spatial resolution and 211u001esensitivity are understandably low but it is possible to coarsely map the lateral 211u001eextent of subsurface processes such as steam floods. The second case uses an 211u001earray of traditional point borehole electrodes combined with long-conductor 211u001eelectrodes (steel casings). Although this arrangement provides more data, in many 211u001ecases it results in poor reconstructions of test targets. Results indicate that 211u001ethis method may hold promise for low resolution imaging where steel casings can 211u001ebe used as electrodes but the merits depend strongly on details of each 211u001eapplication. Field tests using these configurations are currently being 211u001econducted.