Free gas transport in the subsurface: Analogues and applications

我们知道自由气体的传输发生在浅层地下，因为人们可以看到它的表达作为气泡在泉，湿地，间歇泉，并作为自由气体的'突破'在挖掘和钻井。然而，我们对“浅”或非盐水区的游离气运移知之甚少。在地下水教科书中几乎没有提到游离气体输运，在教科书或出版的文献中几乎没有概念图。因此，很难设计有效的现场方法来识别，监测和减轻气体通量。从本质上讲，我们不知道地下自由气体输运在概念上是什么样子的，也不知道如何调查或监测其发生。 关于地下游离气体运输的性质和影响的良好科学信息阻碍了两个能源相关领域发展的有力决策和公众接受度：碳捕获和储存（CCS）和泄漏石油威尔斯周围的逃逸甲烷气体迁移（GM 在CCS中，超临界CO2被注入深层地质层，以遏制人为排放到大气中。尽管一个主要的环境问题是自由相气体泄漏到地面，但尚未进行这方面的现场研究。存在超过15个CCS操作，但没有一个被推到“失败”，因此没有观察到游离气体逸出。 非常规油气开发改变了世界能源供应，但由于公众的反对，在许多司法管辖区受到阻碍。挥发性气体（主要是甲烷）从石油和天然气钻井的垂直部分迁移到淡水含水层，已被确定为地下水质量的主要问题。气体运移的最常见证据是“表层套管排气流”（在井套管内）或套管外的表面可观察到的GM。监管机构目前正在努力界定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。 这项工作将研究天然类似物，我们知道在浅层地下的自由气体运输正在发生，以提高我们对如何有效地检测，监测和修复或管理到达新鲜地下水供应和/或地表的自由气体的理解。一个广泛的实地项目将得到特定实验室研究的支持。对加拿大西部沉积盆地非烃类气体分布和异常压力的平行审查将提供近期地质历史中游离气体运移的区域背景。 这项研究的长期目标是开发一个概念模型，指导地下游离气体迁移调查，从而促进公众对能源工业活动的理解，制定适当的政策，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.