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Comparison of Noise Characteristics on an Un-trenched and Trenched Cable Deployed in the North Sea for a PRM SystemNormal access

Authors: L.W. Bjerrum, T. Matveeva, J.E. Lindgård, H.I. Rutledal and A.C.S. Yde
Event name: 76th EAGE Conference and Exhibition 2014
Session: Microseismic Instrumentation and Detection
Publication date: 16 June 2014
DOI: 10.3997/2214-4609.20141050
Organisations: EAGE
Language: English
Info: Extended abstract, PDF ( 1.08Mb )
Price: € 20

Summary:
We investigate the effect of recording microseismic data with an OBS cable trenched approximately 1 m into the seabed, compared to a cable lying on the seafloor. The data is from the OCTIO’s PRM system installed at the Oseberg field in 2013, approximately 140 km off the Norwegian coast. The PRM system consists of 172 4C stations in a digital network. Trenching of the cable lowers the RMS on the crossline stations, most evident on the stations close to the rig. The large effect observed on the crossline component is believed to be due to that the majority of the rig noise comes on the inline component on the sections along the array, and that this noise is so dominating that trenching the cable will only have a marginal effect. Inspecting the spectra, noise is lower in the frequency band 5-30 Hz once the cable is trenched. For the lower frequencies (0.1-0.8 Hz) less noise is observed on the un-trenched cable. The enhanced noise seen in the datasets for the trenched cable in the lower frequency range is thought to be due to the stronger coupling of the stations to the seafloor after trenching, which thereby picks up more signals.


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