Paper Summary
Seismic monitoring has been challenging on the Njord field. The rather weak 4D responses related to production have been difficult to detect due to the noise level in the streamer 4D seismic data and due to dominant overpressure effect after injection. The streamer seismic data was replaced by Ocean Bottom Seismic (OBS) in 2010 and the first repeat was performed in 2014. The 4D noise level is expected to improve using Ocean Bottom Seismic (OBS) due to repeated receiver positions and better coverage closer to installations. However the sensor technologies and the seismic source were not repeated and we show how we accommodated for this. In addition, we will show how the lack of shallow overburden illumination through the OBS acquisition was compensated for using streamer seismic data and imaging with multiples.