Problems Caused by Microbes and Treatment Strategies Monitoring and Preventing Reservoir Souring Using Molecular Microbiological Methods (MMM)

Abstract

The injection of seawater during the process of secondary oil recovery in offshore oilfields supplies huge amounts of sulphate to the prokaryotic reservoir communities. Together with the presence of oil organics and their degradation products as electron donors, this facilitates the enrichment and growth of sulphate-reducing prokaryotes (SRP) in the reservoir, as well as in pipings and top-side installations (Sunde and Torsvik, 2005; Vance and Thrasher, 2005). The activity of SRP causes severe economic problems due to the reactivity and toxicity of the produced hydrogen sulphide (H₂S), one of the major problems being reservoir souring. Besides the use of broad-spectrum biocides or inhibitors for sulphate reduction, the addition of nitrate effectively decreased the net production of H₂S in model column studies (Myhr et al., 2002; Hubert et al., 2005; Dunsmore et al., 2006) and field trials (Telang et al., 1997; Bødtker et al., 2008). The mechanisms by which nitrate addition might affect souring control are (i) the stimulation of heterotrophic nitrate-reducing bacteria (hNRB) that outcompete SRP for electron donors, (ii) the activity of nitrate-reducing, sulphide-oxidising bacteria (NR-SOB), and (iii) the inhibition of SRP by the production of nitrite and nitrous oxides (Sunde and Torsvik, 2005; Hubert and Voordouw, 2007).

This chapter focuses on the microbiology of oil reservoirs with respect to the key microbial communities that are responsible for causing many reservoir problems.