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The 3D ocean bottom cable technique allows for acquiring long offset and wide azimuth seismic data. The use of simultaneous sources reduces the acquisition turn-around and HSE exposure. In shallow water environments, simultaneous source data are highly contaminated by surface waves and interference noise. Poor signal to noise ratio (S/N) affects velocity estimation, wavelet stability and overall image quality. This paper demonstrates the successful implementation of different processing and interpretation tools to deal with these challenges. The initial velocity model was built by extrapolating checkshot corrected sonic velocities along the interpreted key horizons and was subsequently updated to achieve final PSTM velocity. Several passes of noise attenuation were applied. Volumetric curvature analysis was used to monitor and protect fault planes from smearing during the denoising process. Seismic to well ties were continuously monitored to quantify the improvement after each key process was applied and to QC the seismic wavelet through different processing steps. A key factor to achieve a stable wavelet, at the end of the processing in the shallow water environment offshore Abu Dhabi, was the well driven horizon consistent velocity modeling. High seismic to well synthetic cross-correlation was observed on the final processed data due to the high S/N achieved by several passes of denoising, plus attenuation of strong multiple energy by velocity discrimination. High S/N, pickable geological events, and high resolution fault images are some of the key features of the final stacked image. In pre-stack data, long offset information is available to facilitate AVO and AVAz studies. Incorporating geological knowledge in the interpretation of horizons and faults and using well data during the course of seismic processing proved to be effective in obtaining a high quality seismic dataset.

The seismic imaging of carbonate fields offshore Abu Dhabi is complicated by shallow overburden anomalies (e.g. channels, sink holes, karst features, etc.), strong anisotropy and complex multiple generation mechanisms. Noisy data and converted wave energy create further difficulties. All of these pose challenges for conventional time imaging (PreSTM), resulting in structural uncertainty and unreliable reservoir characterization. Successful imaging requires an accurate velocity model. This is important in the shallow overburden area where inaccurately modelled localized anomalies will amplify errors to deeper targets as waves pass through them, creating artificial pull-ups and push-downs. Seismic anisotropy has a key role in accurate subsurface imaging. In this region, anisotropy is complicated, with values ranging from negative delta to large positive epsilon. Inaccurately estimated anisotropy will result in over compensated velocities, and may cause cycle-skipping in diving-wave Full Waveform Inversion (FWI). Shallow water topography and strong impedance contrasts in the area lead to a substantial amount of free-surface and inter-bed multiples. The repetitiveness of the flat mega-scale geology makes it difficult to distinguish and attenuate multiples from primaries. In this paper, we demonstrate that extensive pre-stack depth migration (PreSDM) technologies including Dip Constraint Tomography (DCT), Structural Constraint Tomography (SCT), Vertical Seismic Profile (VSP) constraint anisotropy update and a well-designed de-multiple flow can successfully resolve the challenges mentioned above.

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