Strontium isotope systematics of mixing groundwater and oil-field brine at Goose Lake in northeastern Montana, USA

Authors

Zell E. Peterman, U.S. Geological SurveyFollow
Joanna N. Thamke, U.S. Geological SurveyFollow
Kiyoto Futa, U.S. Geological Survey
Todd M. Preston, U.S. Geological SurveyFollow

Document Type

Article

Date of this Version

2012

Citation

Applied Geochemistry 27 (2012) 2403–2408

doi 10.1016/j.apgeochem.2012.08.004

Comments

US government work

Abstract

Groundwater, surface water, and soil in the Goose Lake oil field in northeastern Montana have been affected by Cl^- rich oil-field brines during long-term petroleum production. Ongoing multidisciplinary geochemical and geophysical studies have identified the degree and local extent of interaction between brine and groundwater. Fourteen samples representing groundwater, surface water, and brine were collected for Sr isotope analyses to evaluate the usefulness of ⁸⁷Sr/⁸⁶Sr in detecting small amounts of brine. Differences in Sr concentrations and ⁸⁷Sr/⁸⁶Sr are optimal at this site for the experiment. Strontium concentrations range from 0.13 to 36.9 mg/L, and corresponding ⁸⁷Sr/⁸⁶Sr values range from 0.71097 to 0.70828. The local brine has 168 mg/L Sr and a ⁸⁷Sr/⁸⁶Sr value of 0.70802. Mixing relationships are evident in the data set and illustrate the sensitivity of Sr in detecting small amounts of brine in groundwater. The location of data points on a Sr isotope-concentration plot is readily explained by an evaporation-mixing model. The model is supported by the variation in concentrations of most of the other solutes.