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Sparse Nodes and Shallow Water - PS Imaging Challenges on the Alwyn North Field
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 78th EAGE Conference and Exhibition 2016, May 2016, Volume 2016, p.1 - 5
Abstract
Summary
Imaging PS-wave data acquired in the shallow water at Alwyn North with ROV-deployed ocean-bottom nodes presented particular challenges due to the sparsity of the receivers. Having ensured vector fidelity of all recorded wavefields, the processing flow made simultaneous use of the PP and PS wavefields at several junctures, including construction of the imaging velocity-depth model, requiring all wavefields to be processed in parallel and in a consistent manner. Shear-wave splitting corrections and PS demultiple were addressed to improve PS data resolution and achieve data consistency. Constructing an anisotropic velocity model based on residual move-out analysis alone was not feasible as the sparse receiver sampling resulted in poor near-offset coverage. To mitigate this full waveform inversion was used to update the P-leg velocity, and surface wave inversion for the S-leg in the crucial near-seabed interval most affected by the slowest shear velocities. Joint PP-PS non-linear tomography was used to refine this velocity model. PS-wave controlled-beam pre-stack depth migration was used extensively to assess the pre-processing as well as to validate updates to the velocity model. The resultant PS-wave data, imaged with a depth model consistent with that used for the P-wave imaging, were thus suitable for joint PP-PS elastic inversion.
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