4D Borehole Electric Tomography for Hydrocarbon Reservoir Monitoring

Monitoring hydrocarbon reservoir during production represents a key issue. Several approaches are currently used for that purpose, including seismic and non-seismic methods. In this paper, we discuss the potentiality of electrical measurements performed in multiple boreholes using electrodes installed directly on the well casing. We show, with experimental measurements, that high signal-to-noise data can be recorded if the electrodes are electrically insulated from the metallic casing. We performed 3D and 4D cross-well tomography of electrical potentials recorded during a small-scale lab experiment in a sandbox reproducing a realistic oil production scenario. Furthermore, we inverted IP (Induced Polarization) data for retrieving 3D electrical chargeability models during the different stages of oil production. Inverting both DC (Direct Current) and IP (Induced Polarization) data allows estimating the percentage of variations of electrical properties (resistivity and chargeability) during hydrocarbon production. All the 3D and time-lapse models are fully consistent with the time-varying distribution of fluids in our experimental sandbox. This result indicates that borehole electrical methods are effective for reservoir monitoring even in presence of metallic casing.