On the application of Fermat's interferometric principle for water-layer velocity reconstruction in OBN data

Abstract

Knowledge of sea water velocity variations is an important issue for subsurface seismic imaging, particularly in 3D and 4D surveys where reservoir variations must be distinguished from those related to spatio-temporal water variations. A very promisingly and highly-resolved alternative to classical water velocity corrections involves the processing of small amplitude reflections observed within the water layer, during typical marine acquisitions with streamers. In this study we investigate the possibility that these very same reflections could be sensed by Ocean Bottom Nodes (OBN), thus helping the development of more detailed water velocity reconstruction for the transmitted arrivals. For that, first we conduct synthetic simulations to obtain the propagated acoustic field, enforcing our focus on its down-going components. Once such water reflections (now transmitted down to OBN location) are identified in the generated responses, some form of Fermat's interferometric redatum can be applied. It is found that such information might be helpful on the development of more detailed water velocity corrections departed strictly from their underlying signature on the transmitted arrivals.