Free gas transport in the subsurface: Analogues and applications

我们知道在浅层地下会发生自由气体的运输，因为人们可以看到它在泉水、湿地、间歇泉中表现为气泡，在挖掘和钻探过程中表现为游离气的“爆发”。然而，我们对“浅层”或非盐分地下水区域的游离气运移知之甚少。在地下水教科书中几乎没有提到自由气体运输，在教科书和出版的文献中几乎都没有概念图。因此，很难设计有效的现场方法来识别、监测和减轻气体流量。从本质上说，我们不知道地下的自由气体运输在概念上是什么样子的，也不知道如何调查或监测它的发生。 关于地下自由气体运输的性质和影响的良好科学信息正在阻碍强有力的政策制定和公众对与能源有关的两个领域的发展的接受程度：碳捕获和储存(CCS)和泄漏油井周围逃逸的甲烷气体迁移(GM) 在CCS中，超临界相二氧化碳被注入深层地质构造中，以遏制人为排放到大气中。虽然一个主要的环境问题是游离气体泄漏到地面，但在这方面还没有进行现场研究。存在15个以上的CCS操作，但没有一个操作被推到“失败”，因此没有观察到游离气泄漏。 非常规石油和天然气开发已经改变了世界的能源供应，但由于公众的反对，在许多司法管辖区受到阻碍。逃逸气体(主要是甲烷)从石油和天然气钻孔的垂直部分向淡水含水层的迁移已被确定为地下水质量的主要关切。天然气运移最常见的证据是“地表套管喷口流动”(在油井套管内)或在套管外的地面可观测到的GM。监管机构目前正在努力定义转基因对提供家庭井水供应的淡水含水层的水质意味着什么，以及如何管理转基因。 这项工作将研究我们知道浅层地下正在发生自由气体运输的天然类似物，以提高我们对如何有效地检测、监测和补救或管理到达淡水地下水供应和/或地面的自由气体的理解。一个广泛的实地项目将得到具体的实验室研究的支持。同时回顾加拿大西部沉积盆地中非烃类气体的分布和异常压力，将提供近代地质历史上游离气运移的区域背景。 这项研究的长期目标是开发一个概念模型，指导地下的自由气体迁移调查，从而促进公众对能源行业活动的了解，适当的政策制定，以及对环境负责的高效能源开发。

We know free gas transport occurs in the shallow subsurface because one can see its expression as bubbles in springs, wetlands, geysers, and as free gas ‘breakouts’ during excavations and drilling. Yet we know little about free gas migration in the ‘shallow’, or non-saline, groundwater zone. There is almost no mention of free gas transport in groundwater textbooks, and virtually no conceptual diagrams in either textbooks or the published literature. It is consequently difficult to design effective field approaches to identify, monitor, and mitigate gas fluxes. In essence we don’t know what free gas transport ‘looks like’ conceptually in the subsurface, nor do we know how to investigate or monitor for its occurrence. Good scientific information on the nature and implications of free gas transport in the subsurface is hindering robust policy-making and public acceptability of development of two energy-related fields: carbon capture and storage (CCS) and fugitive methane gas migration (GM) around leaky petroleum wells In CCS, supercritical phase CO2 is injected into deep geologic formations to curb anthropogenic releases to the atmosphere. Although a major environmental concern is free-phase gas leakage to surface, no field study has been conducted in this regard. More than 15 CCS operations exist, but none have been pushed to ‘failure’, and hence no free gas escape observed. Unconventional oil and gas development has transformed the world’s energy supply, but is impeded in many jurisdictions due to public opposition. Migration of fugitive gases (mainly methane) from the vertical section of oil and gas boreholes and into freshwater aquifers has been identified as the major concern for groundwater quality. The most common evidence for gas migration is either ‘surface casing vent flow’ (inside the well casing) or surface-observable GM outside the casing. Regulators are currently struggling to define what GM means for water quality in freshwater aquifers that provide domestic well water supplies, and how GM be managed. This work will study natural analogues where we know free gas transport in the shallow subsurface is occurring to improve our understanding of how to effectively detect, monitor, and remediate or manage free gases that are reaching fresh groundwater supplies and/or the ground surface. An extensive field program will be supported by specific lab studies. A parallel review of the distribution of non-hydrocarbon gases and abnormal pressuring in the Western Canadian Sedimentary Basin will provide regional context of free gas migration in recent geologic history. The long term goals of this research are to develop a conceptual model that will guide free-gas migration investigations in the subsurface thus facilitating public understanding of energy industry activities, appropriate policy making, and efficient energy development that is environmentally responsible.