ABSTRACT: Regional Migration of fluids through Shaly Sand Sequences: Examples from the Wilcox of Central Louisiana

FUNAYAMA, MASAAKI, Teikoku Oil, Tokyo, Japan, and JEFFREY S. HANOR,* Louisiana State University, Baton Rouge, LA

Recent geochemical studies support the hypothesis that crude oils in the updip Wilcox (Paleocene-Eocene) of central Louisiana were sourced from beds 100 to 150 km to the south. However, some workers have doubted that long-range fluid migration is possible because of the presence of numerous shale interbeds in this fluvial-deltaic sequence. Insight into the degree of lateral and vertical hydraulic compartmentalzation within the Wilcox can be obtained from examination of regional variations in formation water salinity. We have found that dissolution of salt domes has released a significant mass of dissolved salt which has been transported distances exceeding 100 km throughout the entire updip Wilcox, probably in part by density-driven flow. Our work thus supports the concept that the Wi cox is sufficiently continuous hydrologically to have permitted long-range hydrocarbon migration.

There is evidence that hydrocarbons were introduced into the downdip Lower Wilcox and then migrated both updip and up stratigraphic section. Regional variations in the distribution of sands in the Lower Wilcox may have enhanced lateral focusing of hydrocarbon fluids toward present updip areas of production. Significant systematic decreases in API gravity of Wilcox crude oils updip are probably related to selective removal of the lighter hydrocarbon components in a hydrodynamic setting. The resulting increases in hydrocarbon viscosity and density may have been factors influencing regional entrapment.

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)