Schlumberger

Technical Paper: How New Data Acquisition Technique can Complement Full Waveform Inversion and Lead to Improved Subsalt Imaging

Society: OTC
Paper Number: 24141
Presentation Date: 2013
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Abstract

Full waveform inversion (FWI) has become a new tool in recent practice for subsurface velocity model updating. When using FWI, the common scheme was to use data sets that have relatively large offsets of up to 8 km or more and frequencies as low as 2.8 Hz, considering surface seismic acquisition. In terms of the marine environment, wide azimuth towed-streamer (WAZ) or ocean-bottom cable (OBC) data collection provide the above-mentioned specifications. Recent advances in acquiring data, such as the dual-coil method, offer significant improvements in characteristics over WAZ and OBC such as better illumination, lower frequencies, and longer offsets, all of which allow the FWI to more accurately determine the velocity field. In this paper, the dataset that we input to FWI is a result of dual-coil acquisition where the maximum offset is up to 14,300 m with full azimuth distribution. In order to approximate the observed data, the acoustic inversion incorporates anisotropy in the finite difference propagators and uses the true source and receiver depth.

Our results demonstrate that FWI can be used for velocity updates, with the long offsets and low frequencies provided by the above-described dual-coil seismic acquisition. In particular, the shallow section of the model can be significantly enhanced by using FWI, which can result in an improved overall depth image. Furthermore, lower frequencies and longer offsets mitigate the sensitivity of inversion to the initial velocity model by enabling FWI to update the low wave-number component of the velocity model. Finally, we show the reverse time migration depth image improvements by using the FWI-developed velocity field versus the one from the ray-based methodology.

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Full-azimuth, long-offset data acquisition

Dual Coil Shooting
The Dual Coil Shooting technique employs multiple vessels traveling in continuous circles to acquire full-azimuth seismic data with very long offsets.