In situ transformation of ethoxylate and glycol surfactants by shale-colonizing microorganisms during hydraulic fracturing

Abstract

In the last decade, extensive application of hydraulic fracturing technologies to unconventional low-permeability hydrocarbon-rich formations has significantly increased natural-gas production in the United States and abroad. The injection of surface-sourced fluids to generate fractures in the deep subsurface introduces microbial cells and substrates to low-permeability rock. A subset of injected organic additives has been investigated for their ability to support biological growth in shale microbial community members; however, to date, little is known on how complex xenobiotic organic compounds undergo biotransformations in this deep rock ecosystem. Here, high-resolution chemical, metagenomic, and proteomic analyses reveal that widely-used surfactants are degraded by the shale-associated taxa Halanaerobium, both in situ and under laboratory conditions. These halotolerant bacteria exhibit surfactant substrate specificities, preferring polymeric propoxylated glycols (PPGs) and longer alkyl polyethoxylates (AEOs) over polyethylene glycols (PEGs) and shorter AEOs. Enzymatic transformation occurs through repeated terminal-end polyglycol chain shortening during cometabolic growth through the methylglyoxal bypass. This work provides the first evidence that shale microorganisms can transform xenobiotic surfactants in fracture fluid formulations, potentially affecting the efficiency of hydrocarbon recovery, and demonstrating an important association between injected substrates and microbial growth in an engineered subsurface ecosystem.

Identification of Persistent Sulfidogenic Bacteria in Shale Gas Produced Waters

“…Multiple Halanaerobium species have been isolated from shale environments and exhibit thiosulfate-reducing capabilities (Ravot et al, 1997(Ravot et al, , 2005Fichter et al, 2012;Liang et al, 2014Liang et al, , 2016Booker et al, 2017). It appears more likely that thiosulfatereduction is the more prominent sulfidogenic pathway in fractured shale communities, as evidenced by the widespread presence of the thiosulfate-reducing bacterium Halanaerobium (Davis et al, 2012;Struchtemeyer and Elshahed, 2012;Murali Mohan et al, 2013a;Strong et al, 2013;Cluff et al, 2014;Akob et al, 2015;Daly et al, 2016;Mouser et al, 2016;Vikram et al, 2016;Booker et al, 2017;Lipus et al, 2017;Borton et al, 2018;Evans et al, 2019).…”

“…Despite the addition of biocides and the extreme conditions encountered downhole including high salinity, pressure, reducing conditions, and moderately high temperatures (Fichter et al, 2012;Akob et al, 2015;Daly et al, 2016;Nixon et al, 2019) prior studies have identified microbial communities in produced waters from fractured shales in the Antrim, Barnett, Burkett, Utica, Bakken, and Marcellus formations in the United States (Davis et al, 2012;Struchtemeyer and Elshahed, 2012;Murali Mohan et al, 2013a,b;Strong et al, 2013;Wuchter et al, 2013;Cluff et al, 2014;Akob et al, 2015;Daly et al, 2016;Liang et al, 2016;Lipus et al, 2017;Evans et al, 2018) as well as the Sichuan Basin in China (Zhang et al, 2017). A common finding in many of these studies, is a transition from high diversity microbial communities in injected fluids, resembling the freshwater environment the water was sourced from, to an enriched and lower diversity community of mostly halotolerant and halophilic facultative and strict anaerobes, such as Halanaerobium (Davis et al, 2012;Struchtemeyer and Elshahed, 2012;Murali Mohan et al, 2013a;Strong et al, 2013;Cluff et al, 2014;Akob et al, 2015;Daly et al, 2016;Mouser et al, 2016;Vikram et al, 2016;Booker et al, 2017;Lipus et al, 2017;Borton et al, 2018;Evans et al, 2019).…”

“…Additionally, the formation of microbial biofilms may impede gas flow and result in fracture clogging (Bottero et al, 2010). Evidence suggests that organic chemicals used during hydraulic fracturing may stimulate these deleterious processes, for example via organic acid production from fermentation reactions, and sulfide production from sulfate and thiosulfate reduction pathways (Struchtemeyer et al, 2011;Liang et al, 2016;Booker et al, 2017Booker et al, , 2019Nixon et al, 2017;Evans et al, 2019). Sulfate-reducing bacteria (SRB) have been identified previously in production fluids through next generation sequencing but their in situ role in sulfide production is undetermined (Davis et al, 2012;Struchtemeyer and Elshahed, 2012;Liang et al, 2016), whereas TRB have been isolated from these environments and represent an alternative route to sulfide production (Ravot et al, 1997(Ravot et al, , 2005Liang et al, 2016;Booker et al, 2017;Lipus et al, 2017).…”

Emerging Trends in Biological Treatment of Wastewater From Unconventional Oil and Gas Extraction

“…In another study on PEG and PPG degradation under aerobic conditions in sediment-groundwater microcosms amended with PW (Rogers et al, 2018), authors suggested that primary alcohol dehydrogenase (PA-DH) genes present in the dominant group Pseudomonas could explain the removal of PEG and PPG. Evans et al (2019) demonstrated that PPG, PEG and AEOs were likely to be degraded by pduCDE followed by pduP (aldehyde dehydrogenase gene) mapped to Halanaerobium in PW samples and in laboratory experiments with an isolate, Halanaerobium congolense WG10.…”

“…These surfactants are generally present as a mixture of homologs and are identified by calculation of Kendrick mass defect from LC-MS data ( Thurman et al, 2014 ). A few recent studies have investigated biological attenuation of surfactants in the event of FPW spills ( Heyob et al, 2017 ; Rogers et al, 2018 ) or in natural-gas wells during production ( Evans et al, 2019 ) or during treatment for beneficial reuse ( Hanson et al, 2019 ). Heyob et al (2017) investigated removal of surfactants (Propylene glycol, PPG and commercial surfactants containing NPEOs, AEOs, and PPG-PEG co-block polymers) in soil-groundwater microcosms under anaerobic conditions.…”