Feasibility of EM Monitoring – Acquisition and Inversion

In the last years the possibility of using the electric resistivity as a DHI has strongly raised the interest of the oil and gas exploration community in the EM methodology. But the ability to directly address the nature of the fluids points also to EM in problems related to the reservoir management (OWC detection, CSS application). This paper discusses some aspects of the feasibility of EM to monitor, from the earth surface, the motion of fluids in a reservoir. We have chosen this particular subject owing to the large contrast in the electrical properties between the fluids in the reservoir. Indeed if the spatial variation of a contrast of the order of 1:100 at a depth interesting the oil industry cannot be handled, it is doubtful that EM would be useful when more subtle changes are involved.