Geochemical Markers of Anaerobic Biodegradation in Crude Oils

Carolyn M. Aitken¹, Martin Jones¹, Steve Larter², Arlene Rowan¹, and Ian M. Head^1
1 University of Newcastle, Newcastle upon Tyne, United Kingdom
² University of Calgary, Calgary, AB

Most of the world's petroleum reserves have been biodegraded, with a high biodegradation risk being associated with shallow reservoirs in the deep water continental margin areas of the world currently being actively explored. Aerobic degradation of petroleum hydrocarbons at the surface is well documented and it has long been believed that flow of oxygen and nutrient-bearing meteoric waters into reservoirs was necessary for in-reservoir petroleum biodegradation. Metabolites such as aromatic and aliphatic succinic acids and, more recently, naphthalene carboxylic acids and reduced naphthalene carboxylic acids from the anaerobic oxidation of hydrocarbons have been reported from laboratory enrichment cultures and from studies of anoxic zones in petroleum contaminated aquifers. We recently reported the first direct evidence for anaerobic hydrocarbon degradation in oil reservoirs, having isolated metabolites (reduced naphthoic acids) from a large fraction of degraded oil samples from around the world including the volumetrically important Canadian tar sands. Preliminary findings from laboratory studies of anaerobic crude oil degradation under iron III-reducing, sulphate-reducing and methanogenic conditions have revealed both hydrocarbon degradation and cycloalkyl, aromatic, and polycyclic aromatic succinate metabolite formation. The abundance and distribution of such metabolic markers in naturally occurring degraded crude oils, which is also now being studied may, together with other geochemical information, allow improved predictive models for petroleum biodegradation in reservoirs to be constructed.

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