Integrated inversion of TEM and seismic data facilitated by high penetration depths of a segmented receiver setup

Abstract

ABSTRACTResearch aimed at improving and developing methods for noise reduction in the transient electromagnetic method (TEM) has resulted in an alternative strategy for performing TEM measurements called the segmented receiver coil setup. The measurement strategy involves the simultaneous use of two receiver coils and the resulting TEM data sets have demonstrated signal‐to‐noise ratio improvements of up to a factor of 25 when compared to the traditional setup. This significant improvement has opened up new opportunities for deeper penetration and hence an enhanced integrated inversion with seismic data sets. A case study is presented in which the segmented receiver coil setup is employed in the western part of Denmark. Previous geophysical investigations performed in the same area include multi‐channel reflection seismic measurements and SkyTEM measurements performed with an early version of the SkyTEM instrument having a limited depth of investigation. Deep structures recognized in the seismic data therefore remained unresolved in the SkyTEM data. Notably the elevation of the highly conductive Palaeogene clay, expected to be encountered at approximately 300 m depth in the area, has not been determined by the use of SkyTEM data. With the increased signal‐to‐noise ratio of the segmented receiver coil setup it is possible to resolve resistivity changes to greater depth and thus to achieve an enhanced integrated inversion together with the seismic data. The geological setting between depths of 200–300 m, which is effectively only mapped two‐dimensionally along seismic lines, can be mapped three‐dimensionally using the segmented receiver coil setup. In order to obtain the most reliable geological information, from the TEM data individual soundings are inverted in 1D utilizing the seismic data as a priori information thereby optimizing every single inversion model setup to the local sedimentary stratification. Ultimately, the larger penetration depth is the key to an improved geological understanding of the study area, because the integrated interpretation of seismic and TEM data sets yields valuable lithological and structural information that cannot be resolved by either data type alone.