Isotopic indications for the origin of formation water at the Activo Samaria - Sitio Grande oil field, Mexico

Age determination with the C-14 method resulted in a Late Pleistocene age (16,550-37,900 years) for the infiltration of surface water into the Samaria-Sitio Grande petroleum reservoir, located at a depth between 3500 and 4500 in. The wide range of the isotopic-chemical composition of formation water indicates (a) the infiltration of two components, meteoric and evaporated marine water, during glacial period, (b) the existence of multilayer aquifers, and (c) restrictions on the lateral migration of regional flows. Chemical and isotopic tendencies reflect lateral migration processes of a hypersaline aquifer (Upper Cretaceous) and a brackish aquifer (Middle-Lower Cretaceous) from the Cactus reservoir towards the Nispero reservoir in NE direction, forming an aquifer of intermediate composition. SW-NE directed microfractures within the carbonate reservoir represent the most effective medium for flow migration. Normal and reverse tectonic structures can function in ambiguous mariner as hydraulic barriers and/or pathways. The detection of injected tritium tracer in-the Sitio Grande camp gives indirect evidence for hydraulic flow pathways on a local scale, although the direct arrival of injected surface water and residual brine in production wells was not detected by environmental isotope studies. (C) 2003 Elsevier Science B.V All fights reserved.