Gulf of Mexico Shelf:


Reservoir “Evolution” as CIO-detection “cutoff” becomes more severe (lower impedance)

Movie #3: Shows a VoxelGeo-animated map-view of various D3D* Common-Impedance Objects (CIO's) interpreted to represent EPL's newly discovered (December 2002) CIB CARST sand reservoir at Eugene Island Block 27.  This is a so-called "Impedance Evolution" movie, because the animation starts out showing a "maximum" sized CIO, grown from the CIB CARST gas sand level in the EPL #1 well, and interpreted to represent a connection (through a possible common aquifer) between the CIB CARST sand gas pay in the EPL #1 well and the CIB CARST sand gas that was produced (after 1996) from the Norcen #2 well, in EI-46 to the south.  In the first frame of this CIO, some of the VOXELs on the fringe are believed to represent water-bearing sands, not gas-filled reservoir sands. In the next frame (using a detection threshold slightly more restrictive than the one that allowed the connection with the field to the south), all the VOXELs that represent undetected, non-reservoir rocks are transparent, because they are too high D3D-impedance to be considered to be part of the EPL #1 reservoir. They were not "detected" by VoxelGeo, and hence were not included within the second frame's CIO outline, using a specific D3D-impedance threshold (or "cutoff") value.  In the frames following this second one, each VOXEL has a volume of approximately 0.555 acre-foot per VOXEL (or 3D-seismic sample), and the same map-view is shown with successively lower and lower D3D-impedance VOXELs being stripped away from the shell of the preceding CIO.  The reservoir seems to "shrink" as the D3D-impedance detection threshold is tightened (the value is made more negative, in VoxelGeo).  The final frame shows the smallest, "sweetest spot" in the CIB CARST sand body, with the opaque yellow VOXELs indicating the lowest D3D-impedance (possibly maximum porosity and minimum water saturation).

These yellow VOXELs are interpreted to be the best effective porosity and permeability, CIB CARST reservoir sands in direct communication with the EPL #1 bore hole.  Other high quality sand compartments are probably also connected to this well, but through poorer quality (higher impedance "baffles") sand or silt pathways, that would restrict the flow of fluids to the production perforations.

A flat base is also observed on this CIO, on a high-resolution vertical D3D-impedance seismic profile (above to the left).  This was interpreted to indicate the presence of a gas-water (or oil?) contact, over 120 feet down dip, and suggested that this reservoir might have water-drive pressure support, independent from the up-dip water, that probably ended the production of the Odeco #4 well, in 1984.  EPL drilled its #1 well with a 100% Working Interest, and the gas reservoir made over 5 BCFGE in eight months of production. No formation water has been reported, by March 2004, but the pressure was declining consistent with pressure depletion, suggesting that the flat base may reflect diagenetic cementation, along this very old gas-water contact.

These animated snapshots were made from D3D-reprocessed seismic data.  The data were recorded in 1995, using a 55' x 55' x 3 ms seismic sampling interval, and reprocessed to obtain a 2 ms digital two-way-time sample interval. Two milliseconds of two-way-time equals approximately 10 feet of thickness, using the logged 10,000 feet per second, speed-of-sound in the local gas sand.


VTV, Incorporated, gratefully acknowledges written permission to publish these images, granted by EPL, and Fairfield Industries, the owner of these multi-client seismic data.

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