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Geophysical reservoir characterization in a complex geologic environment remains a challenge. Conventional amplitude inversion assumes reliable seismic amplitudes. In a complex environment, inadequate illumination of the subsurface due to complex geology or the acquisition geometry has detrimental effects on the amplitudes and phase of the migrated image. Such effects are not compensated for in conventional seismic inversion techniques. Consequently, an imprint of various nongeological effects will manifest themselves in the results of seismic inversion, leading to a less reliable estimation of the resultant acoustic and elastic parameters. The depth domain inversion workflow uses point spread functions to capture the dip-dependent illumination effects due to acquisition geometry and complex geology. The amplitude inversion is performed in the depth domain and the output is an acoustic impedance volume corrected for illumination effects. This paper presents the results of a field data example with the objective of comparing the results of the time domain inversion and the depth domain inversion, identifying and explaining both differences and similarities. This leads to an assessment of what should be expected from the depth domain inversion approach, including key advantages and limitations.

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Multisensor streamer acquisition records both pressure and acceleration in the vertical and crossline directions. It enables the reconstruction of a dealiased representation of the upgoing pressure wavefield at any location within the streamer array. This is achieved by joint reconstruction and deghosting using a generalised matching pursuit (GMP) algorithm. To achieve an independent and quantified evaluation of the reconstruction quality, recorded seismic data is compared with the reconstructed seismic data at a witness streamer location. This paper presents the concept and results of this witness streamer experiment. The results show that mitigations can significantly reduce the impact of the main assumption of the GMP algorithm, which could otherwise compromise the quality of the early-time reconstruction in shallow water. Using these techniques, the reconstruction quality compared with an independent witness streamer is consistent from the shallow part to the deeper part of the data, with a very good match between the recorded and reconstructed data.

A narrow azimuth survey and an overlapping Coil survey were acquired and processed for TOTAL offshore Angola. After fast track processing, a direct comparison showed that at a specific location a subsalt steeply dipping event was better defined on narrow azimuth image than on the Coil image. This case study illustrates how illumination analysis can be used to make critical survey design, acquisition and processing decisions. The initial flower plot analysis helps determine the survey design requirements to illuminate target horizons, and will fully justify the need for a full azimuth design. Then, an acquisition illumination analysis complements the previous analysis by creating offset and azimuth illumination maps for chosen design. This identifies illumination and shadow zones on the target horizon. This can be directly related to the seismic data and used to design an appropriate processing solution. Finally, during the processing phase, the specific azimuth contributions identified from illumination analysis need to be separated into azimuthal images. These are intelligently stacked to create the final image, using an intelligent stacking method, designed to retain azimuth specific contribution. To use the full benefit of Coil Acquisition, this two-steps processing strategy derived from the illumination analysis, is essential.

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The Argentina Austral Malvinas survey comprises 13,784 km of 2D data extending from the shelf to the border with the Falkland Islands. The survey was acquired using a 12,000 m streamer and continuous recording technology and was processed through a comprehensive broadband prestack depth migration workflow focused on producing a high-resolution, high-fidelity data set. Source- and receiver-side deghosting to maximize the bandwidth of the data was an essential ingredient in the preprocessing. Following the broadband processing sequence, a depth-imaging workflow was implemented, with the initial model built using a time tomography approach. Several passes of anisotropic reflection tomography provided a significant improvement in the velocity model prior to full-waveform inversion (FWI). Using long offsets, FWI made use of additional information contained in the recorded wavefield, including the refracted and diving wave energy. FWI resolved more detailed velocity variations both in the shallow and deeper section and culminated in an improved seismic image.