IMAGING PRODUCTION AND STIMULATION USING STEEL CASED BOREHOLES

Using the steel casings of existing boreholes in an oil field, we are obtaining images of changes in formation electrical properties resulting from EOR stimulation. Using standard petrophysical relationships, these data can be interpreted to infer fluid behavior during production. High-resolution electrical resistance tomography (ERT) using multiple electrodes installed in boreholes has proven useful for characterization and process monitoring. Installing multiple downhole electrode arrays for high-resolution imaging can be costly on an oil field scale. For these cases, we are exploring the potential to image and track changes in the formation resistivity using the steel casings of existing boreholes as electrodes. The use of existing field infrastructure has several advantages in fielding and in survey fidelity. Data interpretation is accomplished using existing codes that treat the fully 3D case and model the casings embedded in a formation with realistic electrical structure. The surveys produce time dependent maps of the changes in formation resistivity caused by stimulation/production. Using vertical casings alone, only lateral resolution is obtainable. If horizontal casings are available, vertical resolution may be provided as well. In the first field example, we use Archie’s law to calculate changes in the net oil/water ratio from a zone exhibiting ambient temperature changes in electrical resistivity.

This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.