High-resolution depth imaging of long-offset 2D data using full-waveform inversion: The Malvinas Basin, Argentina

Spectrum’s Mike Saunders, Milos Cvetkovic, teamed with Laurence Letki, Monica Hoppe, Lewis Goss, and Ahmed Rady,  in the March issue of The Leading Edge, to discuss the use of Full-Waveform Inversion (FWI) in the Argentina Austral Malvinas survey and how it improved seismic imaging.

The Malvinas Basin lies offshore Argentina, east of Tierra del Fuego, between the Dungeness Arch and the Malvinas (Falkland) Islands and is attached to the North Scotia transform boundary (Galeazzi, 1998) (Figure 1). The Malvinas Basin is mapped as a triangular depocenter extending for some 300 km north–south and 350 km east–west at its southern boundary along the fold belt paralleling the North Scotia transform fault. The wedge-shaped basin reaches a maximum depth of approximately 10,000 m at its deepest point, with a sedimentary fill of Jurassic- to Holocene-aged succession of mostly mud-prone marine siliciclastic strata.

The evolution of the Malvinas Basin consisted of three main phases typical of a passive tectonic margin: rift, sag, and foredeep (Galeazzi, 1998). Grabens oriented in a north–northwest direction were created during Jurassic-aged rifting and were filled with continental sediments of volcanic and pyroclastic origin. During the Late Jurassic sag phase, there was diminished faulting with generalized subsidence accompanied by the deposition of a basal transgressive marine wedge. The tectonically quiescent Late Cretaceous interval generated mud-prone offshore sedimentation, and by the early Paleogene the development of the foredeep trough was initiated by transtentional tectonism. The basin was partially filled with outer shelf glauconite-rich sandstones, basinal claystones, and localized carbonate buildups. The actual foredeep phase was initiated by a strong deepening event in the middle Eocene-Oligocene, resulting in the development of the Malvinas foredeep. This phase also resulted in the formation of compressional structures in the foreland.

The Argentina Austral Malvinas survey comprises 13,784 km of 2D data extending from the shelf to the border with the Falkland Islands (Figure 2). The survey was acquired using a 12,000 m streamer and continuous recording technology, resulting in a data set with excellent imaging from the mudline to the deep basement. The acquisition parameters are summarized in Table 1.
The data were processed through a comprehensive broadband prestack depth migration workflow. In this paper, we review the key steps of this processing sequence with an emphasis on fullwaveform inversion (FWI) as a standard part of the modelbuilding workflow.

As the seismic industry redefines itself, modern 2D exploration programs require more economically efficient business models. The integration of geologic and geophysical workflows has proven to be a successful strategy to achieve this for large-scale multi-client programs in frontier basins (Cvetkovic et al., 2016). The time and depth velocity model-building workflow applied to this program presents a robust methodology that provides reliable models while reducing the overall timeline.

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High-resolution depth imaging of long- offset 2D data using full-waveform inversion: The Malvinas Basin, Argentina