--> Abstract: Bioavailability – the Crucial Control in Sequential Petroleum Alteration, by Heinz Wilkes, Andrea Vieth, Ann-Kathrin Scherf, J. Urgen Rullkotter, Rolando Di Primio, and Brian Horsfield; #90039 (2005)

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Bioavailability – the Crucial Control in Sequential Petroleum Alteration

Heinz Wilkes1, Andrea Vieth1, Ann-Kathrin Scherf2, J.ürgen Rullkötter2, Rolando Di Primio1, and Brian Horsfield1
1 GeoForschungsZentrum Potsdam, D-14473 Potsdam, Germany
2 Carl-von-Ossietzky Universität Oldenburg, D-26111 Oldenburg,

Biodegradation of hydrocarbons in petroleum reservoirs has major economic and technological impact. A characteristic feature of in-reservoir biodegradation is that the process appears to be sequential with respect to molecular structures. The resulting compositional alteration is the molecular basis for the changing physicochemical properties of petroleum and the decreasing oil quality as assessed for example by decreasing API gravity. The important but yet unanswered question is: Why does biodegradation of different oil constituents proceed at different rates? Importantly, from an energetic viewpoint it is not advantageous for microorganisms to prefer certain hydrocarbon substrates over others. In this presentation we will show that the highly variable bioavailability of various petroleum constituents is the main key to understand sequential petroleum alteration. Microorganisms need liquid water to exist and biodegradation takes mainly place at or near the oil water contact. As a consequence petroleum constituents are available for microbes only when they are dissolved in water. Therefore, bioavailability and hence degradation rates of individual petroleum constituents in oil reservoirs are to a large extent controlled by the physicochemical processes controlling their transport to and into the water phase such as diffusion and partitioning. We will use results from laboratory experiments simulating biodegradation of crude oil by anaerobic microorganisms and field data from biodegraded oil reservoirs to show that this concept is applicable to a broad range of hydrocarbon and non-hydrocarbon constituents of petroleum.

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