New Aspects in Acquisition of Long Offset Marine Seismic Data for Sub-salt Imaging

Abstract

Long offset seismic data is required to derive accurate subsurface velocities and anisotropic parameters of the reservoir and overburden rocks. The requirement for long offset acquisition is particularly important for subsalt exploration, due to the large depth of the subsalt reservoirs, complexity of the salt bodies covering the reservoirs, and the anisotropic properties of the sediments above and below the salt. Full Waveform Inversion (FWI) is a method that has been used successfully in the last years to derive an accurate subsurface velocity model (Vigh et al., 2011). Long offsets (10 to 16 km) and ultra-long offsets (more than 16 km) data are very beneficial for FWI, as it allows starting the iterative inversion process with a less accurate velocity model. For sub-salt imaging this means that the salt bodies do not have to be accurately mapped, and this could speed up the exploration process, because salt interpretation could requires significant effort and time. Acquisition of long and ultra-long offsets for marine towed streamer acquisition using parallel type acquisition geometries, NAZ/MAZ/WAZ/RAZ could be quite expensive as this requires long streamers or additional source vessels. Multivessel coil shooting acquisition is more adequate to economically acquire long and ultra-long offsets, and, in the same time, full-azimuth data.