Microbial community analysis of three hydrocarbon reservoir cores provides valuable insights for the assessment of reservoir souring potential

Three hydrocarbon reservoir cores were obtained from a high temperature non-waterflooded offshore reservoir. All three cores were taken from a 56-m section of the same well. Under sterile conditions, DNA was recovered from the inner section of each core and the microbial community profiles were deduced by sequencing the 16S rRNA marker gene. Taxonomic analysis of the Operational Taxonomic Units (OTUs) recovered, identified a high proportion of members from the Oxalobacteraceae family (38.5%) followed by members from the Pseudomonadaceae and Comamonadaceae families (29.1% and 12.8% respectively). Representatives of all these families are known to degrade hydrocarbons as well as to use nitrate as a terminal electron acceptor under anaerobic conditions. Assuming these predominant microorganisms are indigenous to the reservoir and have not been introduced with the drilling fluids they might exhibit a relatively rapid response to nitrate injection for souring control. On the contrary, very few sulfate reducing bacteria (SRBs) were detected in these cores (< 0.01%) suggesting unfavorable conditions to SRB growth. This however may well rapidly change upon seawater injections in the absence of nitrate addition. This study sets the microbial profiling "baseline" for the prediction of souring through modelling as well as for any upcoming biomonitoring surveys. (C) 2016 Elsevier Ltd. All rights reserved.