Little, Robert E.¹, Jeffrey Nunn² 
(1) Exxonmobil, Houston, TX 
(2) Louisiana State University, Baton Rouge, LA

ABSTRACT: Fluid Migration along Faults? A Study of South Timbalier 54, Gulf of Mexico

Whether faults are barriers or pathways for fluid flow is significant to understanding hydrocarbon migration in petroleum exploration. We used seismic and well data from South Timbalier 54 field in the Gulf of Mexico to see if faults were migration pathways for fluid flow. The South Timbalier 54 field occurs over a salt dome that sits at approximately 3 km beneath the seafloor. The field is characterized by two major faults originating from the salt dome up into the shallow section of the field. We used spatial distribution of pore water salinity to test whether fluids have migrated up the faults. If pore water salinity is higher than the original pore waters in these fluvial/deltaic sediments, then these pore fluids must have come from some other location after burial. The Revil et al. (1998) method was used to estimate salinity from well data using the gamma ray, density, and resistivity logs. The estimated salinity logs indicate pore waters have higher than sea water salinity in two out of the four categorized stratigraphic zones in the 54 field. Mud weight data shows that the top of overpressure occurs on the flanks of the salt dome. We propose that overpressured fluids were forced upward along the side of the salt dome. These fluids dissolved salt from the dome to create brines, which continued an upward migration along the major faults out of the geopressured zone. These brines were then expelled into permeable sediments adjacent to the fault zone during migration.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.