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Wilhelms, Arnd1, Michael Erdmann2, Steve R. Larter3
(1) Norsk Hydro a.s, Bergen N5020, Norway 
(2) Norsk Hydro, 5020 Bergen, Norway
(3) Fossil Fuels and Environmental Geocemistry, University of Newcastle, Newcastle upon Tyne, United Kingdom

ABSTRACT: Easy_Fest versus BDI-Uncertainties in Pre-drill Prediction of Biodegradation Degree in Subsurface Petroleum Reservoirs

We know, in truth, not very much about subsurface petroleum biodegradation! The temperature limits in the subsurface are well known as are the gross effects of degradation on oil composition and physical properties. However, no provably indigenous organism that can degrade hydrocarbons under deep reservoir conditions has yet been isolated from a reservoir and balanced net chemical reactions for the process are not available either. Thus the major reactants and products remain equivocal. Most of the world's oil is degraded and with the major process and organisms contributing to its origin largely a mystery it is time to improve our knowledge! Recently advances in pre-drill prediction have been made with a full blown kinetic model (Easy_Fest-Norsk Hydro)and a TTI based approach (Biodegradation Index-from BHP) allowing prediction of API, viscosity etc. and defining the rates of subsurface petroleum biodegradation. Our studies have allowed development of sensible predictive exploration models and the hypothesis that the 80 ºC temperature limit of biodegradation in the subsurface is the temperature base for life in the nutrient depleted earth. Our kinetic models of subsurface biodegradation show that the timescales of in-reservoir degradation are comparable with the long timescales of field charging. In this poster we compare uncertainties in input to basin models attempting to pre-drill predict API (eg oil charge rates, oil mixing histories, oilfield petroleum residence times, reservoir temperature history) for both BDI and Easy_Fest approaches to provide an analysis of where future efforts should lie and the optimum approach to pre-drill biodegradation prediction.


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