Sulfide Generation by Dominant Colonizing Halanaerobium Microorganisms in Hydraulically Fractured Shales

Abstract

Black shale formations underlay much of the continental United States, and through the use of hydraulic fracturing represent a significant natural gas resource. Despite the use of biocides, Halanaerobium species become the dominant microbial community member in produced fluids from many of these fractured shales, regardless of their location. This accumulation of biomass in pipelines and reservoirs is viewed as detrimental by industry, due to potential for souring (production of H2S), microbially-induced corrosion, and pore clogging by cells and biogenic gases. Sulfide is a particular problem in both conventional and unconventional reservoirs toxicity associated with this compound poses health risks to workers, while biogenic sulfide causes corrosion of steel infrastructure pipes by stimulating cathodic reactions that continuously leach protons from the metal. Here we investigate Halanaerobium biogenic sulfide production from a strain isolated from hydraulically fractured Marcellus Shale using coupled ‘omics’ technologies, geochemical field observations, and laboratory growth experiments. Halanaerobium is a gram negative, obligate anaerobe that ferments glucose to acetate, ethanol, formate, lactate, and hydrogen. Genomic analysis identified the presence of three rhodanese-like thiosulfate:cyanide sulfur-transferases and an anaerobic sulfite reductase capable of converting thiosulfate to sulfide within this microorganism. Proteomics verified these proteins were up-regulated when thiosulfate was present in the growth media. While the growth rate of Halanaerobium is not enhanced by the presence of thiosulfate, an acid volatile sulfide assay could only track sulfide accumulation when thiosulfate was present. With these observations we hypothesize that Halanaerobium uses thiosulfate as a way to remove excess reductant during fermentation. During this process, rhodanese-like enzymes convert thiosulfate to sulfite, which is subsequently converted to sulfide via anaerobic sulfite reductase. These findings emphasize the detrimental effects thiosulfate-reducing microorganisms may play in hydraulically fractured shales, which would go undetected using current industry-wide corrosion diagnostics.

AAPG Datapages/Search and Discovery Article #90258 © 2016 AAPG Eastern Section Meeting, Lexington, Kentucky, September 25-27, 2016