Synthetic modelling study of marine controlled-source electromagnetic data for hydrocarbon exploration

Abstract

The marine controlled-source electromagnetic method (CSEM) is a geophysical technique for mapping subsurface electrical resistivity structure in the offshore environment. It has gained ground in recent years as a tool for remote detection and mapping of hydrocarbon reservoirs as it serves as an independent yet complementary method to seismic acquisition. While CSEM data contains useful information about the subsurface, modelling and inversion are required to convert data into interpretable resistivity images. Improvement of modelling tools will assist in closing the gap between acquisition and interpretation of CSEM data. The primary focus of this study was to explore the limits of our present modelling capabilities in the context of marine electromagnetic scenarios. Software based on the three-dimensional CSEM finite-element forward code CSEM3DFWD (Ansari and Farquharson, 2014; Ansari et al., 2015) was employed in this study. While testing of this software had been expanded to models of relevance to mineral exploration, its performance for models which are representative of marine geologic environments, in particular those which are encountered in offshore oil and gas exploration, had not yet been investigated. In this study, marine models of increasing complexity were built and tested, with the ultimate goal of synthesizing marine CSEM data for three-dimensional earth models which were complete in their description of the subsurface. Computed responses were compared to results existing in the literature, when available. To investigate the capability of the code in modelling realistic scenarios, forward solutions were computed for a marine reservoir model based on the real-life North Amethyst oil field, located in the Jeanne d’Arc Basin, offshore Newfoundland. When the capability of modelling realistic earth models is fully realized, forward modelling may be used to assess the utility of the marine CSEM method as a tool for hydrocarbon detection and delineation in specific offshore scenarios.