Regeneration of unconventional natural gas by methanogens co-existing with sulfate-reducing prokaryotes in deep shale wells in China

Abstract

Biogenic methane in shallow shale reservoirs has been proven to contribute to economic recovery of unconventional natural gas. However, whether the microbes inhabiting the deeper shale reservoirs at an average depth of 4.1 km and even co-occurring with sulfate-reducing prokaryote (SRP) have the potential to produce biomethane is still unclear. Stable isotopic technique with culture-dependent and independent approaches were employed to investigate the microbial and functional diversity related to methanogenic pathways and explore the relationship between SRP and methanogens in the shales in the Sichuan Basin, China. Although stable isotopic ratios of the gas implied a thermogenic origin for methane, the decreased trend of stable carbon and hydrogen isotope value provided clues for increasing microbial activities along with sustained gas production in these wells. These deep shale-gas wells harbored high abundance of methanogens (17.2%) with ability of utilizing various substrates for methanogenesis, which co-existed with SRP (6.7%). All genes required for performing methylotrophic, hydrogenotrophic and acetoclastic methanogenesis were present. Methane production experiments of produced water, with and without additional available substrates for methanogens, further confirmed biomethane production via all three methanogenic pathways. Statistical analysis and incubation tests revealed the partnership between SRP and methanogens under in situ sulfate concentration (~ 9 mg/L). These results suggest that biomethane could be produced with more flexible stimulation strategies for unconventional natural gas recovery even at the higher depths and at the presence of SRP.

Comparison of the Hydraulic Fracturing Water Cycle in China and North America: A Critical Review

“…Previous studies have shown that diverse microbial communities including methanogens coexist with sulfate-reducing microbes with corresponding functional capacities in Sichuan Basin shale gas wells and surface facilities (e.g., storage tanks), and have identified sulfate-reducing and iron bacteria in FPW from the Tarim Basin. 59,126,127 In comparison, sulfidogenic bacteria (e.g., Halanaerobium) and methanogens (e.g., Methanohalophilus) are commonly detected in FPW collected from wastewater storage impoundments 128 and separators in unconventional plays such as the Barnett, Marcellus, Utica, and Duvernay. 81,82,129−135 Studies in North America have examined the adverse effects of microbes that survive in FPW, including infrastructure corrosion and chemical degradation.…”

“…Analysis of FPW microbiology is critical to designing FPW storage, treatment, reuse, and recycling strategies and to understanding downhole biogeochemical processes. Previous studies have shown that diverse microbial communities including methanogens coexist with sulfate-reducing microbes with corresponding functional capacities in Sichuan Basin shale gas wells and surface facilities (e.g., storage tanks), and have identified sulfate-reducing and iron bacteria in FPW from the Tarim Basin. ,, In comparison, sulfidogenic bacteria (e.g., Halanaerobium) and methanogens (e.g., Methanohalophilus) are commonly detected in FPW collected from wastewater storage impoundments and separators in unconventional plays such as the Barnett, Marcellus, Utica, and Duvernay. ,,− Studies in North America have examined the adverse effects of microbes that survive in FPW, including infrastructure corrosion and chemical degradation. ,, Dilution of the fracturing fluid by formation water and the degradation of biocides often limits the performance of biocides in restricting microbial activities. ,, Meanwhile, persistent microbes may use a wide range of organic polymers in fracturing fluids such as choline and ethoxylate and glycol surfactants to adapt to high salinity and build adaptative immunity to survive downhole. ,− In several studies, researchers have performed functional and culture-based metabolite analyses of the key North American shale bacterial genus Halanaerobium, further confirming its capacity for sulfide production, which may cause infrastructure corrosion. − …”

Guar Gum Stimulates Biogenic Sulfide Production in Microbial Communities Derived from UK Fractured Shale Production Fluids

“…1a ). Some species of Shewanella are capable of thiosulfate reduction ( 45 ), and Shewanella were reported as the predominant taxa in production fluids from the Sichuan basin, China ( 46 , 47 ).…”

New microbiological insights from the Bowland shale highlight heterogeneity of the hydraulically fractured shale microbiome

“…The exception is the work of Zhang et al . [ 15 , 16 ] in the Sichuan Basin, China. Interestingly, these studies revealed a lack of organisms that were previously considered ubiquitous (and often dominant) in fractured shale environments, such as Halanaerobium species [ 5 ].…”

“…Interestingly, these studies revealed a lack of organisms that were previously considered ubiquitous (and often dominant) in fractured shale environments, such as Halanaerobium species [ 5 ]. Instead, members of the genus Shewanella were found to dominate [ 15 , 16 ] . Thus, characterizing unexplored fractured shales can aid identifying the processes underpinning the differential distribution of these industry-relevant taxa .…”