T8 Environmental Issues Related to Oil and Gas Exploration and Production I

Sunday, 16 October 2005
8:00 AM - 12:00 PM

PORE WATERS CONTAMINATED WITH OIL FIELD BRINE, OSAGE COUNTY, OKLAHOMA:IMPLICATIONS FOR WATER QUALITY AND ECOSYSTEM HEALTH

Paper number: T8-5
Program: Technical Sessions
Time: 8:55 AM – 9:10 AM

Authors

Abstract

Shallow ground water is contaminated with brine from past and present operations at an oil field production site in northeastern Oklahoma. The contaminated ground water provides a source of salts, metals, and hydrocarbons to sediment and water of adjacent Skiatook Lake. An additional source of contamination at the site is a former brine storage pit of 10 m diameter that is now submerged beneath the lake. Cores of the upper 30-40 cm of lake sediment were taken at an offshore saline seep, at the submerged pit, and at a location containing relatively uncontaminated lake sediment. Pore waters from each 2-cm interval were separated by centrifugation and analyzed for dissolved anions, cations, and trace elements. High concentrations of dissolved chloride in pore waters (200-5000 ppm) provide the most direct evidence of oil field brine contamination and compare to an average value of ~35 ppm in Skiatook Lake. Cl/Br mass ratios of 220-250 in contaminated pore waters are comparable to values from produced water and saline soil extracts collected onshore. Dissolved concentrations of Se, Pb, and Cu in Cl-rich pore waters exceed current USEPA criteria for toxicity to freshwater aquatic life. The offshore seep sustains high concentrations of dissolved Cl at the sediment/water interface. In the pit the dissolved Cl concentrations are highly anomalous only at depths below 10 cm, indicating a combination of recent burial, mixing, and exchange with lake water, and bioturbation in this near-shore setting. Annual contribution of Cl to the lake is estimated to be ~20 kg for the entire area of the submerged pit (diffusive flux dominant), and ~5 kg for an assumed circular seepage area of 1 m diameter (advective flow dominant). Such contributions have minimal impact on water quality in the 323,000 acre-ft lake.