Abstract

Subsalt imaging can pose significant imaging challenges for prestack depth migration algorithms. Large local velocity gradients are usually present. Velocity differences between subsalt sediments and salt can exceed 5500 ft/s (1670 m/s). Additionally, the 3D complexity of the salt can introduce rapid spatial variations in subsalt illumination. A methodology that provides a robust and elegant solution to these issues is beamlet migration which involves decomposing source and receiver wavefields into beamlets during the wavefield extrapolation process. Each beamlet has positional information associated with it due to its wavelet transform basis. Also, each beamlet propagates with a local reference velocity in which the local velocity perturbation is small, resulting in accurate wave propagation. Increased accuracy in wavefield propagation permits improved imaging of sediment reflectivity proximate to salt—a critical issue in achieving exploration/development success.

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