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PETROMAKS-Maksimal utnyttelse av petroleumsreserver

Reinjection of produced water: Effect of nitrate treatment on reservoir souring and microbially induced corrosion.

Awarded: NOK 3.2 mill.

The properties of the injection water influence the microbial population in the water injection system and oil reservoir. Most important are microbially mediated H2S production from the oil reservoir (reservoir souring) and Microbial Induced Corrosion (MI C) of pipelines caused by Sulfate Reducing Bacteria (SRB). Nitrate represents an alternative electron acceptor to sulfate. Nitrate treatment of injection water select for Nitrate Reducing Bacteria (NRB) at the expense of SRB. The effect of nitrate treatme nt has been establish in the laboratory and confirmed by monitoring the microbial community and activity in seawater injection systems. Results from Gullfaks show a decrease in H2S production when the treated injection water reaches the producers. At Vesl efrikk and Gullfaks nitrate treatment also led to reduction in MIC in injection water pipelines. It is now possible to obtain samples of nitrate treated produced water. This allows characterization of the microbial reservoir community following nitrate t reatment. Such knowledge is essential for optimisation of the method, a main objective for this project. Reinjection of produced water changes the chemical properties and the temperature of the injection water compared to seawater. Produced water is hot , saturated with organic oil components which may serve as carbon and energy sources for microbes, and contain mineral nutrients present in formation water. Reinjection therefore changes the active microbial population from mesophilic to thermophilic, and may also increase microbial activity in the system. While thermophilic SRB have been isolated from many oil reservoirs, there is so far no record of thermophilic NRB from similar environments. The competitive situation between thermophilic SRB and NRB i s therefore not known. The project will address the changes in the microbial community resulting from reinjection and evaluate weather nitrate treatment can be used during reinjection of produced water.

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PETROMAKS-Maksimal utnyttelse av petroleumsreserver

Thematic Areas and Topics

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