ABSTRACT
Microbiologically influenced corrosion (MIC) is a global issue, influencing the premature failure of metallic infrastructure and accounting for 20% of all internal corrosion incidences. The objective of this chapter is to advance the fundamental understanding of the influence of temperature and salinity gradients resulting from seawater injection or produced water for reinjection (PWRI) operational practices, on microbial community dynamics and MIC. Anoxic microcosms synthetically simulating the higher-in-salinity PWRI mixing practice of (20:80% ISW:PW), representing the North Sea (NS, 127 g/L TDS) System, and the Arabian Gulf (AG, 212 g/L TDS) System, were incubated at a range of temperatures (15°C, 30°C, 45°C, and 60°C). Temporal changes in sulphide depletion, sulphide production, and sulphate reduction profiles as well as microbial community dynamics, and carbon steel coupon surface morphology changes were monitored. Systematic sulphide depletion profiles were reported in PWRI anoxic microcosms (average NS: 2.63 mM ± 0.23; average AG: 2.15 mM ± 0.32), while a rapid sulphide production profile was reported under 100:0% ISW:PW (42 g/L TDS) (18.05 mM ± 0.11) anoxic microcosms. The systematic PWRI sulphide depletion profiles were corroborated with evidence of no sulphate reduction from initial concentrations (NS: 5 mM–4.6 ± 0.38 mM; AG: 10 mM–9.8 ± 0.60 mM). The possibility for methanogenesis as an alternative electron-accepting process was evaluated, and results ruled out their potential contribution in the observed PWRI sulphide depletion profiles (headspace nmoles opposed to mmoles detected). 16s rRNA gene profiling following Next-Generation Sequencing (NGS) approach was conducted attempting to shed light on the observed Iron (Fe)-Sulphide (S) minerals depletion profile under PWRI anoxic microcosm incubations. Microbial communities of the high PWRI salinity practice were driven by temperature with communities at low temperatures (15°C and 30°C) distinct from those at high temperatures (45°C and 60°C). High salinity PWRI (15°C and 30°C) anoxic microcosms selectively enriched for Halanaerobium sp. which corroborated with the detection of advanced-stage pitting nucleation morphologies on coupon surface (30°C: 0.17–0.22 pits of 20 μm diameter). However, the high salinity PWRI high-temperature (45°C and 60°C) anoxic microcosms were selectively enriched for Woesia sp., Sulfurovum sp., and Gaetbulibacter sp., and corroborated with the detection of advanced-stage pitting nucleations on coupon surface that were higher in numbers and diameter (1400 pits of 50 μm–150 μm) when compared to the 30°C anoxic microcosm incubations. Halanaerobium sp. have been implicated in metabolising substrates in hydraulically fractured wells and may remove excessive sulphide. This may prove beneficial for field operations and have a potential impact on the mitigation of MIC. This chapter eventually proposed a holistic approach incorporating a few pointers to consider when MIC incidence is suspected. This proposed holistic approach may be beneficial for mitigation of MIC in the oil and gas industry operations.
