Metabolic Capability of a Predominant Halanaerobium sp. in Hydraulically Fractured Gas Wells and Its Implication in Pipeline Corrosion

Abstract

Microbial activity associated with produced water from hydraulic fracturing operations can lead to gas souring and corrosion of carbon-steel equipment. We examined the microbial ecology of produced water and the prospective role of the prevalent microorganisms in corrosion in a gas production field in the Barnett Shale. The microbial community was mainly composed of halophilic, sulfidogenic bacteria within the order Halanaerobiales, which reflected the geochemical conditions of highly saline water containing sulfur species (S2O3 (2-), SO4 (2-), and HS(-)). A predominant, halophilic bacterium (strain DL-01) was subsequently isolated and identified as belonging to the genus Halanaerobium. The isolate could degrade guar gum, a polysaccharide polymer used in fracture fluids, to produce acetate and sulfide in a 10% NaCl medium at 37°C when thiosulfate was available. To mitigate potential deleterious effects of sulfide and acetate, a quaternary ammonium compound was found to be an efficient biocide in inhibiting the growth and metabolic activity of strain DL-01 relative to glutaraldehyde and tetrakis (hydroxymethyl) phosphonium sulfate. Collectively, our findings suggest that predominant halophiles associated with unconventional shale gas extraction could proliferate and produce sulfide and acetate from the metabolism of polysaccharides used in hydraulic fracturing fluids. These metabolic products might be returned to the surface and transported in pipelines to cause pitting corrosion in downstream infrastructure.

Keywords: Halanaerobium; biocorrosion; guar gum; halophilic; hydraulic fracturing; thiosulfate reducing bacteria.

FIGURE 1

Schematic diagram of the shale gas production facility in Barnett Shale. Six wells (A1–A6) were drilled in this site and the stars indicated the locations where upstream (UCPW) and downstream (DRW) samples were collected. The distance between the two locations is around 1 km. Severe corrosion was detected in the downstream pipeline where replacement was mandated for maintenance.

FIGURE 2

Relative abundance of major taxa (Genus level classification) in upstream comingled produced water (UCPW). Three biological replicates (1, 2, and 3) were included in the later produced water collected in September, 2012.

FIGURE 3

Phylogenetic relationship of Halanaerobium sp. strain DL-01 (in bold) to other species within the genus Halanaerobium. The accession number of each strain is indicated in the parenthesis. The tree was constructed based on approximately 1362 bp 16S rRNA gene sequences. One thousand bootstrap replications were performed and only those greater than 700 are shown. Bar indicated 2 nucleotide substitutions per 1000 bp.

FIGURE 4

Sulfide (A) and acetate (B) production by strain DL-01 when grown on 0.5% guar gum under fermentative and thiosulfate-reducing conditions. Legends: □, 0.5% guar gum+thiosulfate; △,no guar gum+thiosulfate; , sterile (0.5% guar gum+thiosulfate); ◇, 0.5% guar gum+no thiosulfate; °, no guar gum+no thiosulfate; -, (overlapping data with ), sterile (0.5% guar gum+ no thiosulfate). Sterile indicates that cells of DL-01 were heat killed by autoclaving.

FIGURE 5

Minimum inhibitory concentrations of biocides against Halanaerobium DL-01 based on microbial growth, sulfide, and acetate production relative to sterile controls, which the cells of DL-01 were heat-killed by autoclaving. Black and clear bars indicate the conditions with and without thiosulfate, respectively.