Subsalt Time-lapse Seismic for Reservoir Monitoring Using i4D in Deepwater

Ocean bottom seismic (OBS) provides numerous advantages for reservoir monitoring offshore [Beaudoin et al, 2010; Stopin et al. 2011]. This provides wide azimuth high-fold illumination in a quiet environment that results in high quality seismic data. If done with nodes, these can be placed within meters of previous locations enabling highly repeatable 4D surveys. This is a distinct advantage over streamer surveys as they are difficult to repeat in the Gulf of Mexico due to unpredictable currents. In addition, nodes can be placed in close proximity to infrastructure, eliminating the need for undershooting, thus providing good illumination of targets across the whole field. Finally, nodes provide a scalable option to design and acquire lower-cost surveys for targeted monitoring, the so-called i4D concept. All these advantages make OBS a technically robust solution for 4D seismic reservoir monitoring, especially in deepwater environments. In this paper we apply this method at the Ursa/Princess field, in a structurally complex area (subsalt). We explain how we dealt with the design challenge, present the main results and interpretation, and finish with a business impact summary.