Determining Resistivity from Towed Streamer EM Data Using Unconstrained Inversion - Tie to Well and Discovery Examples

We show that unconstrained anisotropic 2.5D inversion of Towed Streamer EM data in complex geological settings can produce resistivity models that are consistent with both interpreted log and seismic data, and known discoveries. We consider two cases from recent surveys in the Celtic and Barents Seas offshore Ireland and Norway respectively. In the Celtic Sea case we show an example where we have compared the results of unconstrained inversion to publically available log data. Not only is the overall depth trend recovered, but the main variation of the resistivity is captured as well as, in some intervals, comparable average interval resistivity. For the Barents Sea case we show an example resistivity and anisotropy section from one of eight survey lines that traverse the Skrugard discovery across its short axis (about 2km). While the resistivity section highlights that the sub-surface resistivity is complex, the somewhat simpler anisotropy section reveals an anisotropy anomaly that is co-incident with both the lateral, and depth, extent of Skrugard.