Detección y cuantificación de la expresión génica de bacterias anaerobias asociadas con biocorrosión en instalaciones petroleras

Abstract

Produced water is generated during exploitation of oil reservoirs. It could be treated and re-injected in mature reservoirs during Enhanced Oil Recovery (EOR). Water-flooding is a common strategy to enhance oil recovery. The water is injected into reservoir in order to push oil towards producing wells. Maintaining quality and standards of produced water avoids great economic losses during operations; the reservoirs are kept away from oil biodegradation, biogenic souring and biocorrosion. The dsrAB genes encode the alpha and beta subunits of the mature sulfite-reductase enzyme, that catalyses the energy-generating step of sulfite or sulfate during anaerobic respiration in sulfate-reducing bacteria (SRB). The nifD gene encodes the alpha subunit of the dinitrogenase enzyme (NIFD), which catalyses N2 fixation, a process coupled with Fe (III). The aim of this study was to know about the corrosive bacterial communities inhabiting saline produced waters of offshore oil exploitation facilities through retrieving sequences of functional genes, for instance, dsrAB and nifD of Desulfovibrionales, Desulfobacterales and Desulfuromonadales taxonomical orders. Additionally, dsrA gene expression of SRB was assessed in systems with saline connate waters of two offshore non-water-flooded high-temperature oil reservoirs. Five clone libraries were constructed with retrieved sequences acquired from different saline produced waters, with and without biocide dosing. The dsrAB phylogenetic analyses showed SRB such as Desulfomicrobium, Desulfovibrio, Desulfohalobium, as well as Desulfococcus, Desulfosarcina, Desulfobacter, Desulfobacterium and Desulfobulbus. The retrieved nifD genes displayed the Fe (III) reducing bacteria that belong to Desulfuromonadales taxa, such as Desulfuromusa, Pelobacter, Malonomonas, and Desulfuromonas. The relative abundance in all produced waters was quantified as follows: the Desulfovibrionales were represented by 55.28% of analysed clones; the Desulfobacterales by 26.83% and 17.89% for the Desulfuromonadales. Diversity measures calculated by the Shannon index (H’) showed that there was a high degree of diversity between all produced waters; however, dominance in produced water with biocide was detected by a Desulfovibrio taxon. The dsrA expression of active Desulfovibrionales-SRB was assessed in systems incubated at 40 and 60°C with salinity around 100 g/L NaCl. Three main clone-libraries were generated. The dsrA sequences showed Desulfovibrio, Desulfomicrobium and Desulfohalobium, Desulfonatronum (Desulfovibrionales) and Desulfosarcina and Desulfobulbus (Desulfobacterales). Uncultured SRB were the main sequences at 60°C in high salinity. Regarding the dsrA gene expression, it dropped dramatically when systems were set with seawater conditions, suggesting that sulfate reduction took place in the connate water of oil reservoirs at high values of NaCl. The aforementioned results provide further insight into the diversity and activity of halophilic SRB that inhabit water associated with oil reservoirs.