The recovery of shale gas is made possible by horizontal drilling and hydraulic fracturing technologies. The process of hydraulic fracturing involves pumping large volumes of water, sand, and chemicals down well to fracture the shale rock and liberate shale gas. This process is believed to make shale rock more hospitable to microorganisms. Recovered shale gas production fluids offer geochemical and microbiological insights into the engineered deep subsurface. However, there is speculation that the microbial colonization of hydraulically fractured shale gas wells could lead to production issues such as souring, corrosion and bioclogging. The prospect of microbially induced corrosion resulting from the action of sulfide-producing bacteria is a key concern, as the generation of hydrogen sulfide may lead to the pitting and cracking of steel pipelines and infrastructure. Despite the concerns surrounding biogenic sulfide production, little is known about the persistence of sulfide-producing bacteria or the role of fracturing chemicals in stimulating sulfidogenesis. There is a study bias towards North American shale gas wells, with just a hand full of wells studied in China, and no reported studies in Europe. This thesis presents the first microbiological insights into two exploratory shale gas wells in the Bowland shale, UK, representing the first study of its type. In this thesis, geochemical analysis tools are paired with cultivation work and 16S rRNA gene sequencing to offer a detailed analysis of how microbiological communities respond to various imposed conditions. This thesis highlights the importance of thiosulfate-reducing bacteria as key drivers in the biological sulfide production observed in shale gas produced water derived microbial enrichments, alongside a potential role for the microbial disproportionation of thiosulfate. This thesis demonstrates the persistence of thiosulfate-reducing bacteria in aged produced water samples obtained from the Marcellus shale, USA. It also characterizes the microbiology and geochemistry of Bowland shale gas production fluids, representing a previously unexplored environment. We demonstrate the potential for the frequently used fracturing chemical, guar gum, a popular choice of gelling agent, to stimulate microbial sulfide production in Bowland shale enrichment cultures at both atmospheric and elevated pressures, the latter being more relevant to conditions encountered down well. Finally, we present evidence of biofilm formation which could result in reduced gas yields during production. The research presented here highlights the potential sulfide-producing capabilities of bacteria present in shale gas production fluids. Improved understanding of such metabolisms could help guide future fracturing operations and inform future subsurface exploitation endeavours.
- Biofouling
- Microbiology
- Hydraulic fracturing
- Bowland shale
- Halanaerobium
- Anaerobic
Microbial Impacts on Shale Gas Exploitation
Cliffe, L. (Author). 31 Dec 2022
Student thesis: Phd