†National Energy Technology Laboratory, United States Department of Energy, 3610 Collins Ferry Road, Post Office Box 880, Morgantown, West Virginia 26505, United States.
‡Division of Plant and Soil Sciences, West Virginia University, Morgantown, West Virginia 26505, United States.
Environ Sci Technol. 2015 Jun 2;49(11):7048-55. doi: 10.1021/acs.est.5b00765. Epub 2015 May 15.
Marcellus Shale occurs at depths of 1.5-2.5 km (5000 to 8000 feet) where most geologists generally assume that thermogenic processes are the only source of natural gas. However, methanogens in produced fluids and isotopic signatures of biogenic methane in this deep shale have recently been discovered. This study explores whether those methanogens are indigenous to the shale or are introduced during drilling and hydraulic fracturing. DNA was extracted from Marcellus Shale core samples, preinjected fluids, and produced fluids and was analyzed using Miseq sequencing of 16s rRNA genes. Methanogens present in shale cores were similar to methanogens in produced fluids. No methanogens were detected in injected fluids, suggesting that this is an unlikely source and that they may be native to the shale itself. Bench-top methane production tests of shale core and produced fluids suggest that these organisms are alive and active under simulated reservoir conditions. Growth conditions designed to simulate the hydrofracture processes indicated somewhat increased methane production; however, fluids alone produced relatively little methane. Together, these results suggest that some biogenic methane may be produced in these wells and that hydrofracture fluids currently used to stimulate gas recovery could stimulate methanogens and their rate of producing methane.
马塞勒斯页岩层的深度为 1.5-2.5 公里（5000 至 8000 英尺），大多数地质学家普遍认为，热成因过程是天然气的唯一来源。然而，最近在该深层页岩中发现了产物流体中的产甲烷菌和生物成因甲烷的同位素特征。本研究探讨了这些产甲烷菌是源自页岩本身，还是在钻井和水力压裂过程中引入的。从马塞勒斯页岩岩心样品、预注入流体和产出流体中提取 DNA，并使用 16s rRNA 基因的 Miseq 测序进行分析。页岩岩心中存在的产甲烷菌与产物流体中的产甲烷菌相似。在注入流体中未检测到产甲烷菌，这表明这不是一个可能的来源，它们可能是页岩本身的固有微生物。页岩岩心和产出流体的台式甲烷生产测试表明，这些生物在模拟储层条件下仍然存活并活跃。为模拟水力压裂过程而设计的生长条件表明，甲烷产量略有增加；然而，仅流体本身产生的甲烷相对较少。这些结果表明，这些井中可能产生了一些生物成因的甲烷，并且目前用于刺激天然气回收的水力压裂液可能会刺激产甲烷菌及其产甲烷的速度。
