Inhaltsbereich
Mechanisms and effects of petroleum biodegradation
Scope
Aerobic biodegradation of hydrocarbons and crude oil is a long-known and well-studied process. In contrast, the capability of anaerobic microorganisms to oxidize hydrocarbons and utilize crude oil as a complex organic substrate is a discovery of the last decade. Today we know that all major types of anaerobic respiration (denitrification, sulphate reduction, ferrous iron reduction) and even methanogenesis may be coupled to the specific oxidation of hydrocarbons. This has strong implications for the understanding of oil alteration since oxygen is unlikely to be available in sufficient amounts to enable efficient aerobic biodegradation in many reservoirs. Aerobic and anaerobic biodegradation are easily distinguished based on their highly specific mechanisms resulting in specific patterns of hydrocarbon depletion and metabolite formation.
Aerobic biodegradation of hydrocarbons and crude oil is a long-known and well-studied process. In contrast, the capability of anaerobic microorganisms to oxidize hydrocarbons and utilize crude oil as a complex organic substrate is a discovery of the last decade. Today we know that all major types of anaerobic respiration (denitrification, sulphate reduction, ferrous iron reduction) and even methanogenesis may be coupled to the specific oxidation of hydrocarbons. This has strong implications for the understanding of oil alteration since oxygen is unlikely to be available in sufficient amounts to enable efficient aerobic biodegradation in many reservoirs. Aerobic and anaerobic biodegradation are easily distinguished based on their highly specific mechanisms resulting in specific patterns of hydrocarbon depletion and metabolite formation.
Furthermore, rates of hydrocarbon oxidation are extremely variable with different electron acceptors (O2 > NO3- > Fe(III) > SO42- > CO2) suggesting a major influence of respiration types on the time scale of in-reservoir biodegradation. Based on results of laboratory expriments with denitrifying and sulphate-reducing bacteria we have suggested that the activity of anaerobic bacteria in petroleum reservoirs can be traced by i) specific compositional changes of crude oil; ii) transformation products specific for the metabolic pathways of anaerobic bacteria; and iii) the carbon isotopic fractionation of the residual hydrocarbon substrate(s). For some oil fields corresponding observations have been reported which suggest anaerobic rather than aerobic oil degradation, however, a sufficient data base for assessment of the importance of different degradation mechanisms and degradation rates under different in situ conditions is still lacking. Specific objectives of this project are:
- Determination of biodegradation effects on oil quality prior to production
- Quantification of extent of biodegradation
- Assessment of respiration types and dominant mechanisms
- Determination of biodegradation effects on oil quality prior to production
- detailed molecular characterisation of biodegradation sequences
- definition of new molecular parameters to assess biodegradation effects
- correlation of molecular parameters with crude oil quality
- Differentiation of biodegradation and water washing effects
- Quantification of extent of biodegradation
- Assessment of respiration types and dominant mechanisms
- aerobic versus anaerobic
- predominances of different anaerobic respiration types
- correlation to biodegradation rates
Participants
- H. Wilkes
- A. Vieth
- R. Elias
- B.S. Pedersen
Partners
- ENI
Funding
- IPP