The origin of aqueous sulfate in Frio pore fluids and its implication for the origin of oil field brines

  • Dworkin S
  • Land L
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The O and S isotopic composition of aqueous SO4in saline formation waters from the Frio Formation of S Texas can be used to deduce the origin of the SO4. The average O and S isotopic composition of aqueous SO4in Frio brines is +13.4‰ SMOW and +8.2‰ CDT, respectively. The O isotopic compositions fall within the range of Mesozoic and Cenozoic seawater values and are interpreted to be derived from dissolved Jurassic evaporites. The S values appear to have been modified by the addition of light S derived from the oxidation of pyrite. We conclude, therefore, that some of the chemical components in Frio brines are derived from water-rock interactions that occurred in much deeper units and that these components have migrated into the Frio.

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  • S. I. Dworkin

  • L. S. Land

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