FATE AND INTERACTIONS OF ORGANIC COMPOUNDS IN PRODUCED-WATER RELEASES: RESULTS FROM THE OSPER “A” SITE, OSAGE COUNTY, OK

About 20 billion bbl of formation water are currently co-produced annually in the USA with oil and natural gas. The large database on the geochemistry of this produced water shows salinities from ~3,000 to >350,000 mg/L TDS. Chloride, Na and Ca are generally the dominant ions, and concentrations of Fe, B, and NH3 may be high. The concentrations of dissolved organics, including monocarboxylic (mainly, acetate and propionate) and dicarboxylic acid anions, BTEX, phenols and poly aromatic hydrocarbons (PAHs) can be very high (up to ~1,000 mg/L as DOC), especially in produced water obtained from young reservoir rocks at temperatures of 80 to 120 oC. We are investigating the transport, fate, natural attenuation and ecosystem impacts of organic compounds, and inorganic salts present in releases of produced water and associated hydrocarbons at the Osage-Skiatook Petroleum Environmental Research (OSPER) sites, located in Osage County, OK. Data from nearby oil wells show that the produced water source is a Na-Ca-Cl brine (~150,000 mg/L TDS), with relatively high concentrations of Mg, Sr, and NH4, but low SO4 and H2S. Dissolved organics, including, organic acid anions, BTEX, phenols and PAHs are relatively low. The source oils are paraffinic-naphthenic light crude, containing n-alkanes as the dominant components unimpacted by biodegradation. The surficial oil releases at the depleted OSPER “A” site are similar, but vary in stages of biodegradation. Repeated sampling of 44 wells from this site show a plume of high salinity water (2,000-30,000 mg/L TDS) at intermediate depths, that extends beyond the visibly impacted areas, and intersects the adjacent Skiatook Lake, a 4250-hectare potable water reservoir. No liquid petroleum was observed in this plume, but hydrocarbon gases, organic acid anions, BTEX and other VOCs are present. Microbial populations are degrading the crude oil and water-soluble organic compounds. The concentrations of the redox-sensitive inorganic and organic species and make-up of the microbial populations indicate that the system is poised at the level of iron reduction. Results show that significant amounts of salts from produced water and petroleum releases remain in the rocks of the impacted area after more than 65 years of natural attenuation.