Step 1: Simultaneous GeoStreamer® Seismic and EM Operations.
Delivery of 3D resistivity volumes or 2.5D resistivity sections depends on line spacing, PGS delivers 3D resistivity volumes when adjacent EM sail lines are spaced at 1.5km or less. Once sail line spacing increases beyond 1.5km 2.5D resistivity sections are delivered. The image shows a birds eye view of simultaneous EM and 2D GeoStreamer seismic setup.
Step 2: 3D EM only Operations.
VPGS acquires Towed Streamer ‘EM only’ data in 3D mode over existing or planned 3D seismic surveys. PGS has a Multi-Client EM data library of >15,000 sq. km as of June 2017.
Step 3: Source characteristics.
Source current of the output optimized repeated sequence (top) and its amplitude spectrum (bottom) from Mattsson et al. (2012).
Source signal is very similar to conventional mCSEM described in mCSEM/Field equipment and data processing/step 3. The main difference comes from the need to increase S/N ratio in the measurements to use towed streamers. To do so, a 20-s silent (listening) span from 100s to 120s could be observed. On that duration, noise filtering is performed, relying on a sliding averaging FIR filter (balancing between noise reduction and frequency content) and a Singular Value Decomposition on frequencies. A motion sensor-based noise reduction is also applied to remove a significant part of the noise coming from movement of the sensor streamer in the earth’s magnetic field.
