Pathways, Rates, and Mechanisms of Fluid Flow at the Bay Marchand Field, Offshore Louisiana

Castle, Jennifer L.¹, Jeffrey S. Hanor², Jeffrey A. Nunn¹ (1) Louisiana State University, Baton Rouge, LA (2) Louisiana State University, Baton Rouge,

The presence of salt structures at shallow depth has played a significant role in the hydrogeologic and diagenetic evolution of the northern Gulf of Mexico sedimentary basin. Previous work at the Bay Marchand salt dome, offshore Louisiana, has demonstrated the presence of three hydrogeologic regimes on the southeast flank of the dome. The shallowest is a hydropressured regime having fluids of normal marine salinity. The deepest regime is characterized by overpressured fluids having marine salinities and less. The middle regime is characterized by hypersaline waters formed by the dissolution of salt. Spatial variations in salinity are consistent with the on-going dissolution of the Bay Marchand dome at shallow depth and the development of dense salinity plumes which are moving laterally and down dip from the side of the dome. Previous studies support the hypothesis that fluids are moving along a southeast-trending axis and are mixing vertically and laterally with ambient formation waters. We have expanded this study to include a much more detailed evaluation of water analyses and of log-derived lithofacies, salinity, temperature, and pressure data to quantify our understanding of the pathways, rates, and mechanisms of fluid flow at Bay Marchand. This information combined with a study of cores and of spatial variations in API gravity will help determine the influence of hydrogeology on hydrocarbon quality and sediment diagenesis in this field.