Processes of hydrogen genesis during seismic cycles in active fault zones (ProHydroGen)

在这个项目中，我们计划使用普林斯顿大学Tullis Onstott教授安装的u管- kasma装置，该装置位于Moab Khotsong金矿地表以下3.4公里的Roodepoort石英岩中，与活动断裂带相连接的约600米钻孔中。该井眼是icdp资助的DSeis项目的一部分，用于监测地震引发的原位地球化学和同位素组成的变化以及微生物活动。我们建议将天然气监测系统与u管- kasma装置相结合，这将提供独特的机会，从深层活动断裂面收集最小变化的地流体和未污染的裂缝气体样本。在断裂带地震活动期间，我们预计会有含H2的地气排出，这可能是深层微生物生命的营养来源。使用直接安装在自动u管- kasms气体分离器上的便携式气体分析系统的特定传感器，将连续检测地气，特别是H2和O3。通过对地震前后流体的化学和同位素表征，我们希望能够阐明氢的来源和生成过程，氢依赖于水的O-H键的裂解。结合断裂带的渗透率和孔隙度数据，该研究将有助于了解流体从源向目标深度的不同运移机制。它将回答低地震事件是否会增加隔离流体的连通性，并为已经存在的H2的迁移提供新的途径，或者为水岩相互作用暴露新的矿物表面，并释放新的机械化学合成的H2。对u型管获得的样品进行直接现场分析，将确定地下气体地球化学在地震事件中发生的变化有多快。识别诱发地气峰的地震矩以及震源距离和方向对断层和钻孔的影响。通过收集气体样本并在实验室进行分析，我们将能够评估H2、CH4以及13CCO2和13CCH4的H/D同位素组成的变化程度，并验证它们是否来自相同的来源，以及这些物种之间的同位素交换是否处于热力学平衡状态。惰性气体同位素测量将允许计算裂缝流体的停留时间，也将有助于回答测量的H2/He比率是否与计算的H2/He放射性裂解/放射性成因产量相匹配的问题。气体化学测量数据是描述流体地球化学行为的物理化学模型的重要输入参数，当与地震图相结合时，将更好地约束断裂带地下气化学生产过程的全球丰度。

In this project, we plan to make use of a U-tube-KASMA device installed by Prof. Tullis Onstott (Princeton University) in a ~600 meter borehole intersecting an active fault zone in the Roodepoort Quartzite located 3.4 km below land surface in the Moab Khotsong gold mine. The borehole is part of the ICDP-funded DSeis project and used to monitor seismically triggered changes in in-situ geochemical and isotopic compositions along with microbial activity. We propose the operation of a gas monitoring system combined with the U-tube-KASMA installation, which will provide the unique opportunity to collect samples of minimal-altered geofluids and uncontaminated fracture gases from a deep active fault plane.During seismic unrest of the fault zone, we anticipate that there will be a geogas discharge including H2 which may serve as a nutrient source for deep microbial life. The geogas and especially H2 and O3 will be detected continuously using specific sensors of a portable gas analytical system directly mounted to the gas separator of the automated U-tube-KASMS. With the chemical and isotopic characterization of the individual fluids before and after seismic activity we hope to clarify the origin and the process generating the H2, which rely on cleavage of O-H bonds from water. In combination with data on the permeability and porosity of the fault zone, this research will help to understand different migration mechanisms of fluids from their source to the target depth. It will answer the question if low seismic events increase connectivity of isolated fluids and provide new pathways for migration of already existing H2 or expose fresh mineral surfaces for water-rock interactions, and release fresh mechano-chemically synthesized H2.Direct on-site analyses of the samples gained by the U-tube will determine just how rapidly changes in subsurface gas geochemistry are occurring in response to seismic events. The identification of seismic moment that provokes geogas peaks and the influence of distance and orientation of the focal point to the fault and the borehole should be identified.By collecting gas samples and analyzing them in the laboratory, we will be able to evaluate to what extent the H/D isotopic compositions of H2, and CH4 as well as 13CCO2 and 13CCH4 change and to verify if they derive from the same sources and if e.g. isotope exchange between these species is in thermodynamic equilibrium. Noble gas isotope measurements will allow for the calculation of residence times of the fracture fluids and will also help to answer the question if measured H2/He ratios match with a calculated H2/He radiolytic/radiogenic production yield. The data derived from gas chemical measurements are important input parameters for physico-chemical models describing the geochemical behavior of fluids, and when combined with seismic maps will better constrain the global abundance of the subsurface gas-chemical production processes in a fault zone.