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Pietraszek-Mattner, Sarah R.1, Lisa M. Pratt1 
(1) Indiana University, Bloomington, IN

ABSTRACT: Early-Stage Aerobic Biodegradation of Illinois Basin Crude Oils: A Comparison of Laboratory and Field Experiment Results

The Illinois basin has many active oil seeps. This study investigates the aerobic microbial degradation of Illinois basin oils found in these oil seeps, using both field and lab degradation experiments. The crude oils used in the investigation are sourced by the Devonian New Albany group and an Ordovician source rock. During the field experiment, which involved burial of oil-doped limestone chips in a homogeneous field, degradation of the crude oils commenced after an approximate one-year lag. After two years of natural exposure, microbial degradation of the crude oils was documented by incremental changes in the aliphatic, aromatic, and polar fraction abundances, progressive removal of the n-alkanes, and decreases in the nC17/pristane and nC18/phytane ratios. During the laboratory experiments, degradation of these same crude oils commenced after approximately one day in a microcosm composed of a nutrient mixture, a known quantity of crude oil, and a community of hydrocarbon-degrading microbes enriched from a local oil seep. After twenty days, all n-alkanes were removed and the abundance of the acyclic isoprenoids had begun to decrease. The Ordovician oil began degrading sooner than the Devonian New Albany oil during the lab experiments. This may be due to the microbial enrichment method, which used Ordovician oil as the carbon source and may have introduced a degradation bias towards the Ordovician oils. In both experiments, shifts of up to 2‰ occur in compound-specific carbon isotopic values of the n-alkanes as degradation proceeded with the residual becoming gradually more enriched in C13

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.