Impacts of stray gas migration on shallow groundwater: insights from laboratory experiments and numerical modelling

水平钻井和多级水力压裂的结合为全球能源生产带来了重大变化，通过新技术，可以从以前难以进入的地层中提取天然气，从而增加了天然气的使用量和可用性。非常规天然气（页岩气）资源遍布加拿大，但随着对水资源潜在威胁的担忧不断扩大。关于这些潜在威胁的研究没有跟上发展的步伐，公众的关注，以及我们对控制过程和相关风险的理解的差距，是加拿大进一步发展的重大障碍。一个潜在的风险是天然气（主要是甲烷）从较深的区域泄漏到较浅的含水层，因为气体在密封不充分或损坏的井筒的表面套管外流动。这种游离气体可以溶解到周围的地下水中，导致化学和生物反应，降低地下水质量。需要进行重点研究，以更好地了解影响杂散气体迁移和溶解气体输送的因素，从而制定风险管理和监测对地下水质量潜在影响的最佳做法。本研究将采用高分辨率实验室实验和先进的数值模型相结合的方法来研究杂散气体运移对浅层地下水的影响。一维和二维实验将使用视觉技术跟踪气体流动和溶解，以及分析气体和水样。分析将包括稳定同位素，以评估在饱和区和不饱和区发生的反应。使用两种不同方法的数值模拟将与实验结果进行比较，并相互比较，以评估模型能力并开发新技术。额外的模拟将调查更大规模、更长期的现场情景，以制定监测战略，并建立不同地质和水文地球化学条件下的风险评估框架

The combination of horizontal drilling and multi-stage hydraulic fracturing has created a significant shift in global energy production, increasing the use and availability of natural gas through new technologies that allow the extraction of gas from previously inaccessible formations. Unconventional natural gas (shale gas) resources exist across Canada, but expansion has been accompanied by concern over potential threats to water resources. Research concerning these potential threats has not kept pace with the surge in development, and public concern, along with gaps in our understanding of controlling processes and the associated risks, is a significant impediment to further development in Canada. One potential risk is the leakage of gas (mostly methane) from deeper zones to shallow aquifers by gas flow outside the surface casing of an inadequately sealed or damaged wellbore. This free gas can dissolve into the surrounding groundwater leading to chemical and biological reactions that reduce groundwater quality. Focused research is needed to better understand factors influencing stray gas migration and dissolved gas transport to develop best practices for risk management and monitoring for potential effects on groundwater quality. This study will use a combination of high-resolution laboratory experiments and advanced numerical models to investigate the effects of stray gas migration on shallow groundwater. One-dimensional and two-dimensional experiments will track gas flow and dissolution using visual techniques as well as the analysis of gas and water samples. Analysis will include stable isotopes to assess reactions occurring in both the saturated and unsaturated zones. Numerical simulations using two different approaches will be compared to the experimental results and to each other, to assess model capabilities and develop new techniques. Additional simulations will investigate larger-scale, longer-term field scenarios to develop monitoring strategies and establish a framework for risk assessment under different geological and hydrogeochemical conditions.**