SEISMIC IMAGING WITH OCEAN-BOTTOM NODES (OBN): NEW ACQUISITION DESIGNS AND THE ATLANTIS 4C OBN SURVEY
The limitations in conventional marine seismic surveys such as imaging of complicated geology in the deep water motivate a quest for new and alternative technologies such as OBNs (ocean-bottom nodes). In this study, survey designs for OBN to provide better fold, offset, and azimuth distributions are created. Augmented VSP geometries are also studied and compared with conventional orthogonal geometries. Then I created joint survey design with both VSP and OBN by combining these two surveys. The results show that joint survey design of VSP and OBN has improved azimuth and offset distribution then VSP itself. In this case, limitations with VSP survey such as poor azimuth and offset coverage can be enhanced by combining VSP survey with ocean-bottom nodes. A main challenge with the ocean-bottom nodes is now processing and imaging of the data. The mirror migration technique is an effective solution for this challenge by separation of the seabed hydrophone and geophone data into up-going and down-going waves. In this study, I explained that mirror imaging (imaging from the down-going ghost reflections) can produce better image quality than conventional up-going imaging. To understand the mirror imaging technique, we first generated synthetic dataset to apply this technique. I then apply mirror imaging technique to Seabird’s Seatrial OBN dataset acquired near the Atlantis field in the Gulf of Mexico. To obtain images from down-going and up-going waves, we used Kirchhoff pre-stack time migration (KPSTM), Kirchhoff pre-stack depth migration (KPSDM) and reverse time migration (RTM) algorithms. The results show that mirror imaging of down-going waves provide better illuminated image from shallow subsurface than conventional migration of up-going waves.