A synthetic modelling study and assessment of marine electromagnetic data using unstructured tetrahedral meshes with applications to hydrocarbon exploration in the Flemish Pass Basin, offshore Newfoundland

Marine controlled-source electromagnetic (CSEM) surveying is a geophysical technique for mapping subsurface electrical resistivity structures in the offshore environment. The method is highly sensitive to resistivity contrasts, which result in interpretable electric field responses. This has caused the method to gain attention in recent years concerning its capabilities as a direct hydrocarbon indicator on a three-dimensional scale. The technique has a significant advantage in being both an independent and complementary method to seismic imaging, allowing for considerable opportunities in joint inversion and interpretation using data that has been previously collected. While raw CSEM data contains rich information about the subsurface, modelling and inversion are required to convert such data into interpretable resistivity estimates. To this end, improvement of modelling tools is integral to the quality and accuracy of interpreted CSEM data. This study used forward modelling based on the CSEM3DFWD code written by Seyed- Masoud Ansari at Memorial University. The finite-element method is employed over unstructured, tetrahedral meshes that allow irregular geological contacts to be accurately modeled. 1D and 3D models have been built with two main goals: to assess the accuracy of CSEM3DFWD by comparing results to known analytical methods; and to assess the thresholds of detection in 3D models that are complete with bathymetry, horizons of geological contacts, and reservoir geometries that are analogous to those in the Flemish Pass Basin, ffshore Newfoundland. Matches of these electric field amplitude and phase results with known semi-analytical methods for 1D models verify the accuracy of the modelling method, allowing an assessment study of detectability of likely reservoirs offhore Newfoundland to be carried out. With this ability to generate accurate synthetic CSEM data for realistic Earth models, more educated decisions can be made concerning marine exploration scenarios: the results of 3D CSEM surveys can be more accurately interpreted and more mindful assessments of risk can be made, increasing the likelihood of reaching successful hydrocarbon plays