Optimization of hydrocarbon recovery requires information on the space and time behavior of the saturation of the various fluids present in the reservoir. This is particularly true for oilfields under secondary recovery such as water flooding, where an even reservoir sweep or zones of by-passed oil can be assessed by a proper description of the water front advance.Permanent downhole electrodes have recently successfully been deployed in oil wells.
This technology allows the time variation of the electrode potentials to be interpreted in terms of changes in saturation within the formation. In practice, the depth of investigation of such measurements is however limited. Time-lapse pressure transient is an independent source of information with a greater depth of investigation, therefore provides an adequate complement to the permanent resistivity array measurement.
In this paper, we propose to use pressure build-up from shut-in in association to the electrical measurements. After recalling analytical analogies in both types of measurements, we propose a quick-look method for interpreting the time-lapse pressure transients. We then compare the physical and practical advantages of each type of measurement and the domain of application of the two measurements with respect to fluid and reservoir properties. Finally we propose an example showing the benefit obtained by coupling the two techniques.