Automated Early-Arrival Travel Time Tomography Using Full-Azimuth, Long-Offset Dual Coil Data in U.S. Deepwater Gulf of Mexico

Abstract

Abstract

Multivessel dual coil data acquisition, with full-azimuth and long-offset coverage, has significantly improved our capability in imaging complex subsalt structures. The data also provides extremely valuable refraction energies, including diving wave, head wave and large angle reflections, for velocity inversion and anisotropy analysis. Often we have found the value of coil data is actually in velocity analysis while traditional tomography fails to take advantage of these refraction energies for velocity model building. The automated early-arrival travel time tomography can correctly model these energies and use them to achieve better velocity model for supra-salt sediment.

For this case study, we used 158,000 dual coil shots as input. First we decomposed the shot records into Gaussian Packets, and then we did 4 iterations of automated travel time tomography and achieved outstanding results. First, the updated model has higher resolution and is more consistent with geology than the initial model. Second, the early-arrival travel time errors have been greatly reduced with the updated model. As additional QC we generated multi-azimuths (6 azimuths with 30 degree per azimuth bin) common image point (CIP) gathers for tomography QC and the image gathers are much improved with the updated model, especially for large offsets and wide azimuths. We did reverse time migration (RTM) and observed consistent improvements in the final image.

The key contribution is we have proven that dual coil long offset data contains valuable early-arrival energies that can significantly improve accuracy of velocity and anisotropy parameter estimation. Most people is only focused on improvements in subsurface illumination from dual coil data.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016