Nutrient Supply During Subsurface Oil Biodegradation—Availability of Petroleum Nitrogen Versus Mineral Phosphorus

Thomas B. P. Oldenburg, Steve R. Larter, Barry Bennett, and Haiping Huang
University of Calgary, Calgary, AB

Most of the world's crude oil in reservoirs is biodegraded. Biodegradation of petroleum is an important alteration process with major negative economic consequences for oil production and refining operations. Although it has been suggested in recent years that biodegradation of petroleum in reservoirs proceeds anaerobically little is still known about the processes and the controlling factors on subsurface hydrocarbon degradation. As the supply of hydrocarbons is unlikely to be limiting in oil reservoirs, essential nutrients like nitrogen or phosphorus might control the rate or degree of biological degradation. Here we examine the possibility of crude oil itself providing nitrogen as a nutrient in the form of nitrogen compounds for microbial use. We use excellent natural biodegradation sequences which covered the whole range from low to severe degrees of biodegradation. We suggest that small amounts of petroleum nitrogen can be used during biodegradation at high degrees of biodegradation (> level 4 of Peters and Moldowan, 1993, PM level > 4) but at lower degrees of biodegradation nitrogen as an essential nutrient has to be supplied from other sources, most likely ammonium ion which is abundant in oilfield waters, sourced from clay and other mineral buffers. Phosphorus in contrast is abundant in many reservoir rocks but is at very low concentrations in petroleums. We conjecture that slowly-released phosphorus from mineral dissolution typically feldspars, may be the rate controlling step in subsurface hydrocarbon biodegradation.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005