Study of microbial community composition and corrosion in shale gas flowback water

Shale gas pipeline corrosion occurs in flowback water environment. The microbial community composition in five flowback water samples collected from different blocks in Sichuan basin was studied by 16 S rRNA gene amplification. The weight-loss measurement, scanning electron microscope and energy dispersive spectrometer were conducted to evaluate corrosion of L360N steel. The result indicated Proteobacteria and Firmicutes were both the dominant phyla at the maximum percentage of 59.711% and 59.711% respectively. But the difference in microbial cmmunity composition at the genus level among five samples was significant with only one genus shared by all. The most dominant genera in five samples were Dethiosulfovibrio (14.801%), Marinobacterium (48.830%), Halarcobacter (33.171%), Bacillus (18.205%) and Sulfurospirillum (44.840%) respectively. Some other sulfidogenic genera like Desulfomicrobium (5.894%) and Desulfovibrio (3.569%) were abundant in Yongchuan and Yibin samples respectively. Some other acidogenic genera like Acinetobacter (8.696%), Citrobacter (9.824%) and Alkalibacter (10.230%) constituted a large fraction in Zigong, Luzhou and Yibin samples respectively. And Shewanella, Pelobacter and Stenotrophomonas were dominant in Dazu, Yibin and Zigong samples. The corrosion rates of L360N steel in flowback water were more than 0.2 mm/a, higher than that in simulated water inoculated sulfate-reducing bacteria alone. In the absence of sulfate, the corrosion in Luzhou sample was as severe as others with a low proportion of S in biofilm. It suggested that the corrosion was accelerated by some corrosive species like acid-producing bacteria within microbial community besides sulfate-reducing bacteria that should not be neglected for corrosion control.