3D Decompaction and Restoration of Salt-Cored Fold Structures, Deep-Water Gulf of Mexico

Carlos Rivero¹, Frank Bilotti¹, Robert Boyce², Mike Strickler¹, and Tom Clarke^1
1 Unocal Corporation, Sugar Land, TX
² CHG Geoscience Consulting, Inc, Katy, TX

We present a new methodology that integrates the sequential 3D decompaction and structural restoration of geologic structures. We apply this methodology to pillow–folds from the deepwater Gulf of Mexico, and combine it with detailed geologic observations to show that these structures grew primarily by differential subsidence into the autochthonous Louann salt. Pillow-folds are domical, salt-cored anticlines, several of which occur at or just beyond the Sigsby Escarpment. Recent hydrocarbon discoveries in this structural trend include Cascade, Chinook and St. Malo. Our restoration methodology allows us to describe the structural evolution and deformation of these structures through time, by removing compaction and deformation induced during the growth of the anticlines.

We apply the methodology to 3D geological models built from pre-stack depth migrated seismic data. The surfaces were decompacted and restored at specific time steps defined by the age of each horizon. At each step, the top interval was stripped off and the remaining horizons were decompacted following a model porosity function constructed from well data. After decompacting, we restored the components of folding and faulting observed in the geologic model following a strain-minimization approach proposed by Massot [2002] and Muron [2003].

In systematically decompacting and restoring 3D models at specific time–steps, we recover some representation of paleo-bathymetry as well as the history of the structural trap. The surface geometries commonly exhibit structural lows and highs that we interpret as paleobathymetry defining depositional fairways feeding the salt pillow system. These fairways might have influenced the distribution of prospective facies.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005