Electrical Monitoring of Oil Reservoirs

Because of the large resistivity contrast between oil and brine, monitoring the oil-water contact during production is a potentially interesting technique. However, it is almost not used in practice today. We believe that such a method has possibilities and deserves more attention. The technique can be significantly cheaper than 4D seismic, especially on-land. At TNO we modeled (3D) different borehole-to-surface electrode configurations for monitoring the lateral position of the oil-water contact and inventoried e.g. their sensitivity versus depth of the reservoir. For this we looked at a rectangular reservoir, but also at a “realistic” reservoir with varying porosity and oil saturations derived from reservoir modeling. Results are looked at in terms of the difference between the potential fields (more than using apparent resistivities) at different time steps. In the modeling we see something we call “the dipole of monitoring”, a concept that can help to design effective electrode configurations for a specific hydrocarbon field. It is concluded that borehole to surface electrical monitoring is of interest in the area of reservoir monitoring.