Integrated analysis of Towed streamer EM and dual-sensor seismic data: Application to the Bressay and Bentley heavy oil fields, North Sea

We introduce a method for integrating Towed Streamer EM and dual-sensor seismic data referred to as seismic guided EM inversion. The inversion workflow is initiated by adopting a sparse-layer depth model defined by dual-sensor seismic data to suggest resistivity boundaries without a rigid constraint. This makes good sense when considering the uncertainties in the seismic data from the time to depth conversion, and more importantly, the fact that a reservoir can be hydrocarbon-charged to an unknown degree corresponding to the spill-point or less. The anisotropic resistivity variations within the layers are accommodated by the lower and upper boundaries, which can be estimated by the unconstrained 2.5D anisotropic inversions. We describe in detail the workflow by applying it to a dataset example resulted from a complex geological region where the heavy oil fields known as Bressay and Bentley are located in the North Sea. Seismic imaging over these fields is challenging since they are rich in injectites, having steep and irregular features. There are also other resistive features such as the Balder tuff, granite intrusions and the basement that can interfere with a fully unconstrained EM inversion. The method introduced here is applicable for exploring complex geological regions, in particular in a frontier exploration, where CSEM and seismic data coexist.