Microbial control within the reservoir of unconventional shale gas plays with anaerobic oil and gas systems containing iron sulfide

Microorganisms cause problems within the oil and gas industry; resulting in significant losses related to unconventional shale gas plays, where the predominant problems are loss of conductivity and reservoir souring.  Introduction of microorganisms typically occurs during drilling, hydraulic fracturing, and other processes, due to the poor quality of water used and inadequate microbiological mitigation practices.  Biocide application during hydraulic fracing operations is typically the norm but some of the biocides used are not compatible with the geology of the shale. Iron pyrite has been identified to some level within all the significant shale gas plays within the US; therefore, identifying a biocide that is compatible with the completed geology and demonstrates long term preservation against microorganisms is paramount to maintaining production and reducing the risk for reservoir souring, as well as other microbiological problems downstream. The study described herein is specifically focused on biocidal efficacy in the presence of iron pyrite and identifies a biocide that may provide the necessary control of sulfate reducing bacteria and facultative bacterial growth. The results provided here demonstrate that Kemira’s 24% dazomet (EPA Registration No. 9386-3) is effective at controlling the microbial growth and activity of sulfate reducing bacteria and facultative bacteria to undetectable numbers, as compared to the controls at over 1 x 10⁵ bacteria per mL, for one year in an anaerobic system; potentially providing relief to downstream systems usually affected by microorganisms at the source.