Application of the cross-borehole direct-current resistivity technique for EOR process monitoring—a feasibility study

The cross-borehole resistivity method measures the electrical potential in one well due to direct-current flowing from electrodes located in another well. This arrangement permits the sensing of regions remote from either well. The paper examines the use of the cross-borehole resistivity method in sensing electrical resistivity perturbations caused by steam-floods, water-floods, and fire-floods.

Our examination consists of three parts. We first estimate the magnitude of resistivity perturbations caused by enhanced oil recovery (EOR) processes. We then calculate the theoretical voltage responses, for several theoretical sweep geometries, for a 2.5 acre well-spacing and a hypothetical shallow, heavy-oil field. For ease of computation, we assume that the swept zone is two-dimensional. Finally, we contaminate the calculated voltages with Gaussian noise with a 5% standard deviation and invert them in a least-squares sense to sweep geometry estimates. The starting models for these inversions are dissimilar to the theoretical sweep geometries. After ten or so iterations the estimated sweep geometries agree well with the theoretical geometries when the models are sufficiently well discretized. This shows that interpretation of cross-borehole data can give information about sweep geometries. We conclude that the cross-borehole resistivity technique has promise in monitoring enhanced oil recovery (EOR) processes, particularly when combined with effective inversion schemes.