Electrically Imaging EOR Stimulation Using Steel Cased Boreholes

NEWMARK, ROBIN, Lawrence Livermore National Lab, Livermore, CA; WILLIAM DAILY, Lawrence Livermore National Lab, Livermore, CA; ABELARDO RAMIREZ, Lawrence Livermore National Laboratory, Livermore, CA

We are using the steel casings of existing boreholes as electrodes to image EOR stimulation in the field. High resolution electrical resistance tomography (ERT) using multiple electrodes installed in boreholes is useful for both site characterization and process monitoring. Recent design improvements permit such electrode arrays to be installed to depths appropriate for oil field deployments. In many cases, however, installing multiple downhole electrodes is too costly. For these cases, we are exploring the possibility of using the steel casings of existing boreholes as electrodes, with some success.

Numerical simulations using different configurations of vertical steel casings alone or in combination with point electrode arrays indicate the range of resolution and sensitivity achievable with the ERT method. The results suggest that, although the spatial resolution and sensitivity are understandably lower than that obtained with high resolution arrays, it is possible to coarsely map the lateral extent of subsurface processes such as steam floods. Experiments using physical models support the numerical simulations.

Casing-to-casing ERT surveys using abandoned vertical steel casings are being obtained in an oil field undergoing steam flood. The images reveal changes in electrical properties consistent with independent indicators of steam movement. Difference images show progressive changes in the electrical properties of the field. Resistivity decreases may indicate locations where the steam has substantially penetrated the field. By contrast, electrical resistivity increases during a period characterized by boiler outages.

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California