ABSTRACT: Evans, et al.

Authors:
Frank Evans, Ellen Clark, and Henry Posamentier
Chevron, 100 Northpark Blvd., Covington, Louisiana 70433

Advances in the Tahiti Field Subsalt Seismic Imaging and Interpretation: Utilizing Seismic Attribute Analysis and Offset/Azimuth Partitions for Imaging and Interpreting Deepwater Subsalt Structure and Facies

Session:
U.S. Gulf Deepwater Fields I (GRBCC, Ballroom A)
Monday, September 21, 2015, 10:45 am

Abstract:
The Tahiti Field has significant imaging and interpretation challenges due to its location beneath a thick complex salt canopy and its steeply-dipping strata. The latest full­azimuth dual coil seismic acquisition techniques along with improved processing algorithms, such as full waveform inversion and reverse time migration, have shown good improvement in the subsalt imaging. These technical advances, along with post-processing attribute analysis and enhanced interpretation practices, have brought new capabilities for interpreting this low frequency subsalt data.

Tahiti subsalt seismic attribute analyses have improved structural and stratigraphic interpretations by illuminating subtle features not previously observed. Combining seismic attribute volumes (e.g., coherence, spectral decomposition, dip, azimuth, etc.) with visualization techniques (e.g., volume co­rendering, optical stacking, and stratal slicing) have revealed structural and sedimentary architectures (e.g., faulting and channel complexes, respectively). These interpretations are geologically reasonable and consistent with well log and whole core data interpretations. These results illustrate the potential benefit of using seismic attributes to enhance reservoir characterization and prediction. When combined with standard mapping techniques, this structural and stratigraphic interpretation approach has the potential to reduce compartmentalization risk. As well as, has the potential to improve well placement and reserves estimates, and identify new areas for exploration and development. Tahiti seismic attribute work will continue to add benefit in future development projects by helping characterize and interpret the minor sands above current producing reservoirs. Results will be incorporated into static and dynamic models that will be used for reserves, forecasting, and well placement.

The Chevron Tahiti team is also improving the structural image by utilizing the Vector Image Partition (VIP) data generated by WesternGeco, using their full-azimuth Revolution II survey. With this technique, numerous partial stacks are created based on offset and azimuth. The stacks are then reviewed with a basic structural model in mind, and those stacks (i.e., partitions) that enhance the expected events and dips are combined to create an improved stack. Partitions that do not contribute to the expected image are assumed to be noise and are excluded. This technique was recently utilized in conjunction with salt proximity data to drop the inclination angle while drilling a well, thereby successfully avoiding salt. This presentation will discuss the above techniques, and show examples of the results and the impact on the Tahiti Field.