Geochemistry of Saline Formation Waters, Miocene, Offshore Louisiana

L. S. Land, G. L. MacPherson, L. E. Mack

Forty-seven samples of formation water and associated oil and/or gas were obtained from Miocene reservoirs, offshore Louisiana, and analyzed for major and minor organic and inorganic components. The data suggest mixing of two types of water: a saline type sourced from nearby salt structures, and a Co₂-rich low-salinity type derived from the geopressured zone. Most fields exhibit a pronounced density inversion.

The saline end member is basinal water discharged up the flanks of salt structures, modified considerably by salt dissolution. Enrichment in ¹⁸O and ⁸⁷Sr suggests little impact of surficial (seawater or meteoric) water. The low-salinity end member is seawater extensively modified by sulfate reduction, methanogenesis, contribution of interlayer water from smectite, and mineral/water interactions involving feldspars and clay minerals.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.