--> ABSTRACT: Four-Dimensional Evolution of a Salt-Related Fault Network: Eugene Island Block 330 Field, Offshore Louisiana, by Mark G. Rowan, Bruce S. Hart, Steve Nelson, and Peter B. Flemings; #91019 (1996)

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Four-Dimensional Evolution of a Salt-Related Fault Network: Eugene Island Block 330 Field, Offshore Louisiana

Mark G. Rowan, Bruce S. Hart, Steve Nelson, and Peter B. Flemings

The Eugene Island Block 330 field consists of two anticlinal rollovers in the hanging wall of a listric normal fault system that detaches along a deep salt weld. We use interpretation of well and 3D seismic data, 3D structural restoration, and fault analysis techniques to investigate the evolution of the three-dimensional geometry through time and its impact on hydrocarbon migration and entrapment.

The master fault that currently forms the northeastern boundary of the field originated as two distinct, overlapping fault segments separated by a relay ramp. The segments linked by breaching of the ramp prior to 2.2 Ma. The resultant footwall splay continued to accommodate a significant proportion of the net slip, but became essentially inactive by 1.5 Ma. In the hanging wall of the master fault, interaction between two synthetic splays and an antithetic fault resulted in a similar, complex history of varying displacement distribution.

Analysis of evolving hanging- and footwall cutoff geometries on the various faults suggests that cross-fault hydrocarbon migration at sand-on-sand contacts may have contributed to reservoir filling. This scenario requires that Lentic (>2.2 Ma) sands in the footwall were connected to deeper hydrocarbon sources, which cannot be demonstrated and may be problematic because of the discontinuous nature of these sands. Moreover, the present distribution of hydrocarbons and the sealing nature of faults at some sand-on-sand contacts imply that another mechanism, such as episodic vertical migration along fault zones, is required to introduce hydrocarbons into the shallow reservoirs.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California