Geopotenzial Deutsche Nordsee (GPDN) - CSEM - Cruise No. M88/2 - September 08 - September 22, 2012 - Bremerhaven (Germany) - Bremerhaven (Germany) (English)

Cruise M88/2 was dedicated to conduct controlled source electromagnetic (CSEM) measurements to study the electrical resistivity structure of possibly gas containing shallow sediments in the German North Sea sector. The experiments were part of the joint venture project "Geopotenzial Deutsche Nordsee" (GPDN), coordinated at BGR. During the 13 days cruise measurements were conducted along seismic profiles in two working areas (A and D) northwest and southwest of Helgoland showing strong amplitude anomalies within the first 200 m below the seafloor. Area D was also the target area for the first data acquisition with the new BGR 3-D seismic system during leg M88/1. Two types of seafloor-towed CSEM systems were used: The University of Toronto System and the new CSEM receiver system recently developed at BGR called HYDRA II. While the Toronto system is a completely towed system, the BGR system can be either deployed as a towed system behind the transmitter of the Toronto system, or the receiver modules can be stationary deployed on the seafloor and only the transmitter dipole is towed on the seafloor. CSEM data have been recorded with both systems and configurations. In working area A, CSEM data were only collected with the Toronto system. In working area D high quality CSEM data have been recorded with both systems along overlapping profiles. Stationary receivers were deployed to the North and to the South of the profile. Preliminary analysis of the data demonstrates the first successful deployment of the Toronto system and a very high data quality recorded with the BGR system. Preliminary 1D inversion of the data reveals a layer of moderately increased resistivity which is consistent with the lateral and depth extent of the seismic amplitude anomaly in area D while no resistor can be resolved in area A. Prior to the CSEM deployments the seafloor conditions of the profile lines were surveyed using the shipboard multi-beam and parasound systems. The shipboard CTD/ rosette system was deployed at eight sites to test the handling and compatibility of the BGR methane sensor with the shipboard Seabird CTD. It also provided water conductivity profiles which are used as a-priori information for the CSEM interpretation.