AAPG Bulletin, V. 82 (1998), No. 5B (May 1998 Part B), P. 1055-1082.

Salt-Sediment Interaction, Northern Green Canyon and Ewing Bank (Offshore Louisiana), Northern Gulf of Mexico¹

Mark G. Rowan and Paul Weimer²

©Copyright 1998.  The American Association of Petroleum Geologists.  All Rights Reserved

¹Manuscript received August 19, 1996; revised manuscript received March 24, 1997; final acceptance November 19, 1997.
²Department of Geological Sciences and Energy and Minerals Applied Research Center (EMARC), Campus Box 399, University of Colorado, Boulder, Colorado 80309-0399.

This work represents the culmination of a 4 year, integrated structural and stratigraphic research program that would not have been possible without the contributions of many companies and individuals. Specifically, we thank Halliburton (Bob Graebner, John Anderson, and Gary White) for the bulk of the seismic data; TGS and Exxon for additional seismic data (through Peter Flemings at Pennsylvania State University); Paleo-Data (Art Waterman) and Micro-Strat for biostratigraphic data; and CogniSeis (Roy Kligfield and Bob Ratliff), GeoQuest, and Zeh for software. Funding was provided through the EMARC Gulf of Mexico industrial consortium (Agip, Amoco, Anadarko, BHP, BP Exploration, Burlington Resources, CXY Energy, Chevron, CNG, Conoco, Enterprise, Exxon, Marathon, Mobil, Occidental, PanCanadian, Pennzoil, Petrobras, Phillips, Shell, Texaco, Total, Union-Pacific, and UNOCAL) and by the Department of Energy (through Peter Flemings at Pennsylvania State University). We also acknowledge the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research. We thank Jory Pacht and Hongxing Ge for careful and valuable reviews, Kevin Biddle for his editorial comments, and Brad Prather for a copy of his manuscript. We especially acknowledge our graduate students for their vital contributions: Barry McBride, Peter Varnai, Fadjar Budhijanto, Zurilma Acosta, Rafael Martinez, and Alonso Navarro. 

ABSTRACT

Structural and sequence stratigraphic interpretations of two-dimensional seismic and well data from northern Green Canyon and Ewing Bank were integrated to evaluate how salt deformation influenced the distribution of Pliocene-Pleistocene facies in time and space. Two techniques were employed. First, twelve palinspastic maps of near-surface structure were constructed. These were combined with maps of interpreted depositional environments to show how shallow salt diapirism created bathymetric relief that influenced the configuration of sediment transport systems and depocenters through time. Second, tectonostratigraphic packages comprising multiple sequences were defined based on external geometry. Different stacking patterns of these packages characterize four types of minibasins, each with a distinct history of salt evacuation from underlying salt stocks and sheets. Interpreted seismic facies were analyzed within this minibasin framework to evaluate how deep-salt withdrawal influenced the distribution of depositional systems.

The results show that both structural and sedimentological variables influenced lithofacies development. External factors dictated the volume and type of systemwide clastic input. Regional factors, such as nearby salt structures and the position of deltas, controlled the dispersal of clastics. Local factors, such as the thickness of underlying salt, influenced minibasin-specific evolution. These factors interacted at three scales: (1) a broad transition from sand-rich ponded settings to shale-dominated bypass settings during the Pliocene-Pleistocene, (2) fluctuations over periods of several sequences that created highly variable stratigraphic stacking patterns, and (3) a progression from ponded to bypass facies within individual sea level cycles. Analysis of these various factors can improve the prediction of reservoir distribution within slope minibasins, and thereby reduce the risk in subsalt and deep-water exploration.