Boldly Interpreting Where Geophysics Does Not lead: Using Geologic Observations and Structural Restoration to Confidently Infer Subsalt Geometry Adjacent to Tahiti, DW-GOM

Donald A. Medwedeff¹, Jacob Diedjomahor², and Greg Schoenborn^3
1 Chevron Texaco EnergyTechnology Co, San Ramon, CA
² ChevronTexaco, New Orleans, LA
³ ChevronTexaco, San Ramon, CA

In the eastern deepwater Gulf of Mexico, trap definition and migration geometry are the key risk elements due to poor subsalt seismic imaging. To compensate we developed an interpretation strategy using the relatively well-imaged base of allochthonous salt to constrain subsalt interpretation. The constraint is introduced via a comprehensive geological interpretation which improves the accuracy of seismic horizon mapping.

The Tahiti discovery area comprises a salt stock and canopy system developed by progradation of Cretaceous and Tertiary strata over the Jurassic salt. An Upper Miocene to Pliocene canopy overlies salt stocks. The Tahiti Counter Regional Fault (TCRF) dips NW and strikes NE-SW across the area providing lateral closure to traps on its south side. South of the TCRF, subsalt strata are well imaged and tied to wells. North of the TCRF, subsalt strata are poorly imaged and only indirectly constrained.

The base of the canopy alternately conforms and cross cuts underlying strata. Where conformable the base represents rapid canopy spreading and is treated locally as structural marker. This marker and well data allow for a tightly constrained jump correlation across the TCRF. Horizon maps based on this correlation indicate the TCRF to have >20,000 feet of throw and represent large-scale salt evacuation.

Restored isopach maps indicate that salt evacuation along the TCRF locally controlled sediment accommodation space. Section restoration suggests that the TCRF has been a fluid migration barrier from the Mid-Miocene to the Present and that salt canopy formation occurred at different times and rates across the TCRF.