STRUCTURAL ANALYSIS OF A SALT CORED TRANSFER ZONE IN THE SOUTH TIMBALIER BLOCK 54, OFFSHORE GULF OF MEXICO: IMPLICATIONS FOR SALT RELATED RESTORATION OF EXTENSIONAL STRUCTURES

Offshore Louisiana shelf is aboundant in listric growth systems that are characterized by short, arcuate regional and counter-regional faults that commonly form complex transfer zones above shallow, Miocene level salt bodies. South Timbalier Block 54 (ST 54) constitutes one such area where a basin-ward dipping regional and a landward dipping counter-regional growth fault form a convergent transfer zone. 3D seismic and well data have been used to interpret the structure of four offshore blocks adjacent to ST 54. The interpretation reveals that the eastern and western flanks of the structure contain salt in the footwalls of the main regional and counter-regional faults; the salt rises to a much shallower stratigraphic level in the central part the transfer zone, thus forming a collapsed crest structure. Kinematic restorations have been performed on a series of north-south trending sections, perpendicular to the strike of the major faults, by sequentially removing and decompacting the sedimentary units. The cross sectional area of the salt is assumed to be constant throughout the restoration process due to the incompressibility of the lithologic unit and to provide additional constraints to the geometry of the structure during restoration. The results show that up slope evacuation of salt is a result of sediment loading and growth fault movement and the location of the transfer zone is controlled by the initial geometry of the allochthonous salt. A 3D structural model using depth converted horizons, balanced cross sections and well tops has been constructed to accurately represent the subsurface geometry. A clay experimental model using silicone fluid as an analog for salt and equipped with a 3D laser scanning system, was used to demonstrate and support the mechanisms revealed from the kinematic restoration process and also to gather insights on the movement of salt. Understanding the evolution of the structure in ST 54 provides insight on similar structures in other areas of offshore Louisiana and aides in establishing the relationship between salt evacuation and transfer zone development.