Reservoir Monitoring by CSEM Data: A Fictitious Domain Strategy

Abstract

Abstract Marine controlled source electromagnetic (CSEM) survey is a novel complementary geophysical method for exploring structure below the seafloor. In this research, the processing of marine CSEM data is investigated for monitoring of hydrocarbon reservoirs in the offshore. Due to highly conductive seawater and shallow conductive layers, the attenuation of any EM signals is one of the most crucial problems that has prevented the application of imaging technologies (e.g. migrations) regularly adopted in exploration seismology. Inspired by the similarity of seismic and electromagnetic data, we investigate an innovative approach by applying two popular seismic imaging methods on CSEM data for monitoring of hydrocarbon reservoirs in conductive (attenuating) media: reverse time migration (RTM) and Kirchhoff migration (KM). The synthetic marine CSEM data is calculated for a model including a hydrocarbon reservoir in an attenuating medium. We used the realistic values for sedimentary rocks that are common for attenuating media. Then, we apply RTM and KM methods to CSEM data in the real-time diffusive domain to monitor the hydrocarbon reservoir. In marine CSEM surveys it is important to consider the direction of source implementation and here we model the effects of source implementation directions in terms of reservoir monitoring. Maxwell's equations were solved in the fictitious wave domain, a scheme allows faster calculations than conventional methods, reducing the computational cost. However, the wavefields calculated using this fictitious method are not real and should transferred to the real-time diffusive domain. The results confirm the RTM handles both the vertical and horizontal edges and defines the hydrocarbon reservoir in attenuating media much better than KM since the RTM does not introduce any approximations of the physics of wave propagation. The main drawback of RTM, its expensive computational cost, has been significantly reduced by advent of new powerful computers., The results also show that the horizontal source implementation is a better scheme for reservoir monitoring using a marine CSEM survey.