HANOR, JEFFREYS., Louisiana State Univ., Baton Rouge, LA

Abstract: Thermohaline Pore Water Trends of Southeastern Louisiana Revisited

Work over the past 15 years has established the existence of three major types of subsurface fluid flow regimes in the southeastern Louisiana Gulf Coast. The shallowest consists of topographically-driven, fresh-water systems; the deepest is a regional overpressured regime. There also exists a regional thermohaline regime at intermediate depth where fluid flow is driven in part by differences in fluid density resulting from spatial variations in temperature and salinity induced by the presence of salt diapirs. Understanding the dynamics of thermohaline circulation is critical in understanding controls on hydrocarbon migration, the distribution of fresh water resources, and the fate of injected oil-field and hazardous wastes in salt dome provinces.

A recently published study has questioned the validity of the existence of currently-active thermohaline flow in southeastern Louisiana based on the conclusions that: 1) evidence for large-scale fluid migration is critically founded on salinity values calculated from conventional log techniques, 2) these log techniques are inaccurate, and 3) the analysis of log-derived data for a study area in and around the St. Gabriel Oil Field in southeastern Louisiana indicates that large scale fluid migration there is not dynamic at present.

However, a critical review of existing published studies of formation waters in south Louisiana demonstrates that the evidence for regional thermohaline fluid flow is not based solely on log-derived information, but also on fluid properties determined by direct chemical and isotopic analysis, petrologically-constrained mass balance calculations, and numerical simulation of fluid flow around salt structures. Recalculation of log-derived salinities at the St. Gabriel field demonstrates both that conventional methods are sufficiently adequate in regional studies and that aqueous fluid flow in the area in and around the St. Gabriel field is undoubtedly dynamic at present. 

AAPG Search and Discovery Article #90924©1999 GCAGS Annual Meeting Lafayette, Louisiana