Subsalt Imaging and 4D Reservoir Monitoring Evaluation of Tahiti Field, Gulf of Mexico
Catherine Thacher, Dimitri Bevc, Ellen Clark, Kurt Nihei, Bernard Regel, Joe Stefani, and Larry Sydora
Subsalt reservoirs are usually not considered candidates for 4D seismic monitoring. The argument has been 'If I can't image the reservoir with seismic, how can I hope to see production effects with seismic?' While 4D is a proven industry technology for reservoir monitoring of water floods, its use in the subsalt environment is less prolific. As a cost effective feasibility test of 4D in subsalt reservoirs, we create a 2D visco-elastic anisotropic earth model of the Gulf of Mexico Tahiti field. The model is constructed from water bottom to basement using rock properties derived from Tahiti field well log and cores in addition to general Gulf of Mexico trends. Incorporating the Tahiti reservoir prediction simulation model, we also create a time-lapse version of this same 2D model. Using rock physics relations, we transform the earth/reservoir properties (porosity, water saturation, pore pressure) into elastic properties (Vp, Vs, density). Rooting the model in reservoir properties and rock physics helps ensure an internally consistent set of elastic parameters. We then create 2D synthetic data that are representative of both static and dynamic earth properties. Finally, we process these raw synthetic data in a 4D workflow that includes data conditioning, blind velocity analysis, depth migration, and 4D seismic imaging. The Tahiti 2D/4D models reveal that production effects in these subsalt reservoirs are detected on 4D seismic data. We describe the model building workflow, the products of velocity analysis, and the resulting 4D synthetic seismic images.
AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013