Joint Inversion for Sub-Basalt Imaging at the Mřre Margin, Norway

As hydrocarbon exploration is moving to more geologically challenging areas, the combination and integration of different geophysical data types is often used to improve imaging and to minimize risk. While seismic data in principle provide good resolution, complicated 3D geological structures e.g., basalt structures, may severely affect illumination and imaging. Gravity and magnetics are not affected by basalt structures, but are highly non-unique. Controlled-source electromagnetic (CSEM) prospecting has been established as a new method for directly identifying commercial oil or gas accumulation. The technique is applied in increasingly complex subsurface settings, and is not affected by basalt structures. However, the relatively low frequencies that are required to achieve sufficient depth penetration only allow low resolution imaging. We present our multi-parameter joint inversion approach including seismic, gravity, magnetics, and CSEM, combining the advantages of the individual methods. The vital link between the different models is established using a structural approach based on cross-gradients (e.g., Gallardo and Meju, 2003). The resulting models are uncontaminated by a priori defined empirical relationships between the parameters of the individual models. We present the method and applications to synthetic but realistic sub-basalt data based on the Norwegian Mřre margin.