2D velocity benchmark – EAGE 2004 Frédéric Billette BP EPTG - Advanced Imaging Team 501 Westlake Park boulevard Houston, TX USA Tel.: Fax: With a team of: Sverre Brandsberg-Dahl, John Etgen, Carl Regone & Ganyuan Xia - BP EPT Houston

Complex velocity model building benchmark Goal: snapshot of the state of the art in complex velocity model building. Results will have the opportunity to be presented during the next EAGE meeting in Paris, June Model and data are wholly owned by BP and the attached data release agreement must be signed and returned Data are available for ftp download (7 < 2Gb files) as well as on 3590E or DLT4 tape (contact for details). Data are in SEGY format and total file size is ~ 14Gb.

Data modeling 2D dataset (all Y=0) Finite difference acoustic modeling (variable velocity & density) Free surface (surface-related multiples are present) Vertical derivative of the pressure is recorded. Frequency peak is 27Hz and data can be whitened up to 54Hz The wavelength is causal and has not been 0 phased (see typical trace below), time delay can be estimated considering the zero offset traces.

Data acquisition 1348 shots (200 x 6 files x 1 file for ftp) First shot X = 50m Last shot X = Shot interval = 50m Source depth = 12.5m 2001 time samples - Sample rate = 6ms - First sample = 0ms 1201 receivers First shot: First receiver X= m First shot: Last receiver X = 50m (0 offset) Receiver interval = 12.5m Receiver elevation = 0m S1S2 S1348 Simulates a boat pass from left to right (towards increasing X) Note: there is a –10 scaler noted in the SEGY headers (XYScaler=-10) for the source and receiver X and Y (meaning positions are in cm). The source depth is an integer in the SEGY file: Zsource = 12m but is in reality 12.5m X

Model used to generate the data Origin X = 0m Number of X logs = X increment = 6.25m Origin Z = 0m Number of samples = 1911 Sample increment = 6.25m First or last traces are duplicated as many times as needed when the receiver spread is outside the model X Z

Deliverables described in the next page and any questions should be directed to: Frédéric Billette BP EPTG - Advanced Imaging Team 501 Westlake Park boulevard Houston, TX USA Tel : (1)

Deliverables by April 9 th, 2004 A short abstract describing the methodology and the results. A velocity model in SEGY format as described below: X Z Origin X = 0m Number of traces = 5399 Trace increment = 12.5m Origin Z = 0m Number of samples = 1911 Sample increment = 6.25m Velocities in meter per second

Participation to the workshop Authors will have the opportunity to show their results on a poster during the EAGE workshop (W8) Estimation of accurate velocity macro-models in complex structures (Monday June 7, am – 16.00pm). Authors will be notified of abstract status by May 1 st. During the workshop, results may be compared but only without mention of the author (Model A, Model B, …).