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

加拿大的页岩气资源是一种新兴的低成本、清洁燃烧能源。然而，页岩气井的产量下降速度比常规井快得多，在短短几年内就下降了95%。这就要求钻井或修复更多的油井以维持生产水平，从而增加了成本，消耗了有限的水资源，并且需要处理水力压裂液。产量下降的原因尚不清楚，但主要归因于储层压力下降和储层渗透率随时间的变化。裂缝渗透率代表了主要的流动路径，随着时间的推移，由于支撑剂的降解、裂缝闭合、碳酸盐的沉淀和未培养的微生物群落的生长，裂缝渗透率会降低。后者是众所周知的生物矿化剂，通过其在地下环境中的生长和代谢活动，已观察到影响地下水流动状况。杀菌剂用于保护水库免受污染；然而，我们的团队最近对水力压裂返排液的测试表明，这些杀菌剂仍然只是部分有效，并且亲压和亲热（喜欢压力和温度）的微生物在水力压裂液中生长并填充到相对较高的细胞密度。

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.