Hydraulic fracturing to produce hydrocarbons from shale gas reservoirs involves a water cycle that connects deep geologic formations with water often derived from near-surface sources. The growth of undesirable microbes at various stages of the water cycle often causes facility damage, impacts gas or oil production, and influences the reuse and treatment of fracturing wastewater. Therefore, an improved understanding of the influences of microbial activity, through tracking microbial community dynamics, is key in making the fracturing water cycle more efficient, and ultimately in reducing potential environmental impacts and achieving overall economic benefit. In this study, we tracked the microbial community dynamics of fracturing fluid, flowback wastewater, and produced water from an unconventional well in the Duvernay Formation in Alberta, to establish a temporal, high-resolution profile of microbial dynamics. 16S rRNA gene sequencing and live/dead cell staining were used to assess microbial communities and biomass, and water chemistry was determined to estimate changes in environmental stress and nutrition supply for microbial communities in the water cycle. The results showed that (1) mixing recycled produced water with source water quickly caused a significant reduction of active cells from source water, but microbes which survived this mixing regenerated at later time at surface conditions, and (2) active cells rapidly declined after the initial flowback period, and the total biomass was continuously below the quantification limit in produced water. The results imply that the subsurface environment in the Duvernay Formation may naturally restrict the growth of microbes from surface water, but the reuse of produced water for further fracturing fluids preparation, which contains resilient microbes, may pose a risk of microbial regeneration in the fracturing fluids and biofouling of infrastructure.

Microbial community dynamics in the hydraulic fracturing water cycle of a newly fractured shale gas well in western Canada

253rd National Meeting (2017)

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