Separated Wavefield Imaging Research Articles

Extending subsurface imaging beyond ocean-bottom node coverage using multiples: A case study in deepwater Nigeria

We have evaluated the results of a receiver decimation study in a deepwater context using separated wavefield imaging (SWIM) algorithms to provide extended illumination for imaging without ocean-bottom node (OBN) positioning constraints. We carried out subsurface imaging using the SWIM imaging technique with a reduced OBN layout, and we compared the results with those from conventional one-way wave-equation migration. We found from the results that the SWIM algorithm makes it possible to reduce the OBN layout while obtaining a similar subsurface image with the same shot geometry, which allows a reduced receiver acquisition effort, offers more geometry flexibility without affecting the image quality, with a potentially significant reduction of acquisition cost and 4D processing turnaround time.

Utilizing a novel quantitative interpretation workflow to derisk shallow hydrocarbon prospects — a Barents Sea case study

Large areas of the Barents Sea, such as the formerly disputed zone between Norway and Russia in the eastern Barents, are still undrilled. An exploration licence was recently awarded over the Haapet Dome (PL859) to operators with a prime interest in shallow Jurassic reservoirs (Reiser et al., 2016). Multiple oil and gas discoveries made farther west, such as Goliat and Norvarg, make this part of the world a highly prospective area for hydrocarbons. Traditionally the combination of a hard seabed with relatively shallow water depths has prevented the recording of near offset reflection data for the shallowest sediments. It is therefore not surprising that the presence of shallow hydrocarbons in this area has only recently been revealed thanks to imaging techniques that use the energy from sea-surface reflections which provide the missing near angle information for reliable AVA analysis. This paper describes a regional rock physics study of the Barents Sea and a quantitative interpretation workflow using Separated Wavefield Imaging (SWIM) and Full Waveform Inversion (FWI) to identify leads over the Haapet Dome in absence of direct well information.

Wave-equation multiple imaging (WeMi) — Swimming between the flags

Deghosting dual-sensor streamer seismic data requires separation of the total recorded wavefield into upgoing and downgoing components during seismic preprocessing. Imaging of multiples exploits the wavefield separation process by using the downgoing wavefield at each receiver location as a virtual source. Multiple imaging has been shown to effectively remove shallow-acquisition-related artifacts commonly seen on wide-tow marine seismic surveys and improve imaging quality of the shallow overburden. Acquisition design factors, imaging condition, and cross-talk noise are the main factors that determine the effectiveness of separated wavefield imaging (SWIM) of dual-sensor streamer data. (SWIM is a common nontrademarked acronym used in the literature to describe multiple imaging of separated wavefields sampled from dual-sensor streamer data.) In a field trial, acquisition design did not allow for proper sampling of the total wavefield, with the result that multiple imaging did not prove to be as robust a technique as examples in the literature might imply. Understanding the effects of acquisition design parameters on image quality is essential to more successfully apply multiple-imaging techniques with greater relevance on the North West Shelf of Australia.

Separated-wavefield imaging using primary and multiple energy

Imaging with separated wavefields (SWIM) is an innovative depth-imaging technology that uses upgoing and downgoing wavefields at the surface to deliver high-resolution images of the subsurface. It takes advantage of the extended illumination provided by surface-multiple energy, and thus, it exploits data that the seismic industry historically has treated as unwanted noise. The fundamental concept behind SWIM is based on using each receiver as a “virtual” source, effectively expanding the surface coverage of the seismic experiment and enhancing the subsurface illumination, particularly for shallow reflectors. By effectively turning the streamer spread into a source (and receiver) array, the resulting equivalent survey has spatial sampling that is much improved and a richer distribution of offsets and azimuths. The improved spatial sampling enhances the angular illumination greatly at every image point. Therefore, SWIM produces densely sampled angle gathers that provide greater opportunities for velocity-model building and for improved interpretation of complex structures. Several issues need to be considered for proper imaging with SWIM: migration-imaging conditions, attenuation of cross talk, and acquisition design. The latter must be addressed to support proper sampling of both upgoing and downgoing wavefields used for imaging. A broad overview and examples of these subjects are presented. Applications to a deepwater wide-azimuth (WAZ) survey from the Gulf of Mexico and a shallow-water narrow-azimuth (NAZ) data set from offshore Malaysia demonstrate the enhanced areal illumination and improved imaging resolution from imaging using multiple-reflection energy.

Enhanced subsurface illumination from separated wavefield imaging

Shaoping Lu, Dan Whitmore, Alejandro Valenciano and Nizar Chemingui present applications of separated wavefield imaging to a deepwater wide-azimuth survey in the Gulf of Mexico and to a narrow azimuth data set from offshore Malaysia.

Mitigation of the 3D cross-line acquisition footprint using separated wavefield imaging of dual-sensor streamer seismic data

Mitigation of the 3D cross-line acquisition footprint using separated wavefield imaging of dual-sensor streamer seismic data