ABSTRACT

Isotopic analyses of twenty brine samples from two salt diapir-related oil fields and one growth fault-related gas field in southern Louisiana lend support to the model proposed by Workman and Hanor (this volume) that brines from the zone of geopressure are mixing with hydropressured formation waters along the flanks of the Iberia salt dome and, within the limits of the sampling, suggest that this hydrodynamic process may be characteristic of the region. ¹⁸O, D and ⁸⁷Sr/ ⁸⁶Sr determinations suggest that formation fluids above 2000 m (6500 ft) depth have partly equilibrated with terrigenous clastic rocks. Fluids below 2000 m (6500 ft) appear to be mixed Oligocene/Miocene seawater and clay-mineral water or evolved hydrocarbon-bearing water. These fluid compositions vary with depth due to mixing and possibly to temperature variations. Some samples may contain constituents derived from salt dissolution.