Exploiting the Airwave for Land CSEM Reservoir Monitoring

Displacement of oil by saline water leads to time-lapse differences in CSEM measurements. Because the time-lapse effect may be weak and difficult to observe, acquisition optimization plays an important role. Applying a horizontal dipole source on the surface creates a source-induced airwave component. We studied the effect of the airwave on time-lapse land CSEM measurements of resistivity changes after oil production by running numerical simulations for several configurations. Our study shows that the source-induced airwave is the predominant component in increasing the amplitude of the time-lapse fields, the difference between the recorded EM data before and after oil production. Moreover, the lateral extent of the depleted part of the oil reservoir is much better defined when the airwave is present.