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Velsect Automatic Velocity Analysis

Velsect Automatic Velocity Analysis. General approach. Digitise sea floor and “base” events Where there is no data – or no moveout Create a rough water-depth based velocity field Create water-depth based NMO stretch mutes Filter data : tight band-pass and RADON

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Velsect Automatic Velocity Analysis

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  1. Velsect Automatic Velocity Analysis

  2. General approach • Digitise sea floor and “base” events • Where there is no data – or no moveout • Create a rough water-depth based velocity field • Create water-depth based NMO stretch mutes • Filter data : tight band-pass and RADON • Generate velocity spectra and pick • Edit based on geological values • Extract low-spatial frequency component

  3. Avoiding Misspicks • Cycle skipping – different parts of same event • Band pass filter AND limit picking increment • Distorted semblance – multiples/diffractions • RADON filtering in “signal out” mode • High or low velocity trends • Reject picks on interval velocity – iteratively • Dip effects • Pick iteratively; stacks and preSTM data • Mispicks deleted prior to extracting trend

  4. Raw VELSECT picks Base horizon location can be easily identified Velocity trends are already clearly visible at this stage

  5. Edited VELSECT picks V-T pairs that give rise to interval velocities outside the range 1520m/s and 6000m/s rejected, iteratively. Aorund 30% of all V-T pairs rejected

  6. Final VELSECT picks 1.5km radius low-pass spatial frequency filter used to extract trend and remove jitter

  7. Final VELSECT results Water depth based velocities (left) and VELSECT velocities (right); note that dip and multiple are still present and this represents a first pass velocity field only

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