Measurement of impact of microbial processes on fracture permeability and fluid flow in hydraulic fracture systems

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Canada’s shale gas resources represent an emerging low-cost, clean burning energy source. However, production output from shale gas wells has been seen to decline much more rapidly than conventional wells, dropping up to 95% after only a few years. This requires that ever more wells need to be drilled or reconditioned to maintain production levels, thereby increasing costs, use of limited water resources, and need for disposal of hydraulic fracturing fluids. Reasons for these production declines are poorly understood, but are ascribed to loss of reservoir pressure and changes in reservoir permeability over time. Fracture permeability represents the predominant flow path and can decrease over time due to degradation of proppants, fracture closure, precipitation of carbonates, and growth of uncultivated microbial communities. The latter are well known agents of biomineralization and through their growth and metabolic activities in subsurface environments have been observed to influence groundwater flow regimes. Bactericides are used to protect the reservoir from contamination; however, recent testing of hydraulic fracturing flowback fluids by our team have shown that these biocides remain only partly effective and that piezophillic and thermophillic (pressure and temperature loving) microbes grow in and populate hydraulic fracturing fluids to relatively high cell densities.