Dating of oil field brines using 129I

Abstract 129I/I ratios are reported here for oil field brines from two fields in Louisiana and one in Utah. In two cases, the ratios obtained indicate good agreement between the age obtained with the 129I system and the formations the waters were found in. In the third case, the 129 I I ratios are significantly above the decay curve for 129I and suggest a contribution of recent surface waters to the brines. Comparison to results concurrently obtained for 36 Cl Cl and 87 Sr 86 Sr ratios indicates that the 129I system is best suited for determinations concerning the origin and history of organic matter in aqueous fluids.