Sulfate reducing bacteria, nitrate reducing bacteria and their interactions in a souring offshore oil reservoir

Fan, Fuqiang (2018) Sulfate reducing bacteria, nitrate reducing bacteria and their interactions in a souring offshore oil reservoir. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The troublesome souring issues, especially those occurred in offshore oilfields, have plagued petroleum and environmental industries for decades. To control reservoir souring, the nitrate addition have been noticed in recognition of their safety and operational effectiveness. The interactions between sulfate reducing bacteria (SRB) and nitrate reducing bacteria (NRB) are key mechanisms in the nitrate-mediated souring control. However, much is still unknown towards the effective profiling of SRB and the detailed NRB-SRB interactions. Although NRB produced biosurfactants might be promising bio-agents affecting NRB-SRB interactions, very limited studies tackled the production of biosurfactants by natural NRB strains. Systematic investigation of their unique roles in enhancing NRB competence over SRB was not documented. This thesis targeted on filling the above stated gaps and examined SRB, NRB and their interactions in a souring offshore oil reservoir system. A method based on phospholipid fatty acid (PLFA) profiling of microbial communities in offshore produced water was developed and optimized. The developed method was further applied to profile microorganisms and trace SRB. Biosurfactant producing NRB was isolated and the associated biosurfactant product was used for tracking NRB-SRB-biosurfactant interactions. The outputs of this thesis include: (1) the established PLFA based protocol for profiling SRB in offshore reservoirs; (2) the successful isolation and identification of biosurfactant producing NRB coupled with subsequent biosurfactant generation and characterization; and (3) the findings to confirm, for the first time, that NRB-produced biosurfactants could significantly strengthen SRB inhibition by NRB. The thesis has resulted in promising products and scientific observations for aiding souring control in the challenging offshore reservoir environments.

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