2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 3
Presentation Time: 2:15 PM


WARREN, Ean, HOSTETTLER, Frances D., GODSY, E. Michael, PAGANELLI, Victor V. and KHARAKA, Yousif K., U.S. Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025, ewarren@usgs.gov

During a multidisciplinary study at two oil production sites of differing ages near Lake Skiatook, Osage County, Oklahoma, a series of oil, water, brine, and soil samples were characterized and analyzed for microbial populations and geochemical parameters that are indicative of microbial activity. Petroleum wells and production tank batteries at site “A” have been inactive for some time and the bulk of the hydrocarbon (now degraded and weathered oil) and produced water releases occurred more than 65 years ago. One pit at this site, however, contains relatively fresh asphaltic oil and high salinity brine. In contrast to site “A”, site “B” (located approximately 6 km away) includes an active production tank battery and adjacent brine and oil pit, an inactive tank battery and an injection well with a small brine pit. The area source oils are light, paraffinic-naphthenic crude oils, containing n-alkanes as the dominant components and are unimpacted by biodegradation, even though petroleum production is from shallow sandstones (300-600 m depth). The oils at the inactive site “A” are similar to each other in their chemical fingerprints, although in varying stages of biodegradation. The n-alkanes in oil samples taken from surface pits at the active site “B” do not appear to have undergone significant biodegradation yet. Microbial populations at both sites are degrading the water-soluble, low-molecular-weight, aromatic, n-alkane, and the more refractory n-alkylcyclohexane compounds from the crude oil. The high dissolved Fe(II), low nitrate and other geochemical evidence, as well as the composition of the microbial populations at both sites indicate that the systems are poised at the level of iron reduction. However, the progression of n-alkylcyclohexane loss (higher molecular weight homologs are lost first) within some deeper, more degraded samples suggest that some methanogenesis has occurred. Populations of aerobic, fermentative and iron-reducing microorganisms are on the order of 100 times greater at site “A” compared to site “B”, reaching concentrations of 100,000 organisms per gram of sediment. Contamination has been present for a longer time at site “A” than site “B”, allowing for a longer growth period.