Towards Evaluating and Managing Risks Associated with Legacy Wells and Offshore Gas Storage in Scotland

在全球努力实现净零排放的过程中，碳捕获和封存(CCS)将在减少温室气体排放和应对气候变化方面发挥至关重要的作用。海上二氧化碳储存为长期储存提供了一个有前景的解决方案；然而，评估、管理和减轻与海上二氧化碳储存设施失去遏制相关的风险是至关重要的。据估计，英国大陆架的二氧化碳储存量为80-90GT(ETI UKSAP，2011)。苏格兰皇家地产(CES)负责租赁距离苏格兰海岸12至200英里的天然气储存资产，这是一个拥有广泛石油和天然气勘探和生产历史的海底区域，自20世纪60年代末以来已钻探了7,000多口井。CES管理的可用于潜在天然气储存的海底面积约为7500平方公里，横跨苏格兰海岸线。在任何地区选择最佳的天然气储存地点时，都必须考虑可能导致失去安全壳的风险因素，并评估一旦安全壳受损，后果的严重性。这种风险筛选工作对于确定最佳储气区、筛选风险较大的区域以及在基于风险的决策过程中使用至关重要。决定近海储存区总体风险状况的因素包括地质完整性和建筑、遗留基础设施和完整性、海床稳定性以及任何可能因失去安全带而受到影响的环境受体的存在和性质。特别令人担忧的是遗留油井及其完整性，苏格兰近海环境中存在数千口这些油井。在近海地质储存期间，遗留油井是围堵的主要风险，在近海地质储存期间，完整性可能会受到损害，从而使逃逸的天然气向海床和海洋环境迁移。目前，还没有专门针对苏格兰近海环境的传统油井风险筛选工具、方法或战略，可以帮助管理、优化和确定苏格兰近海储气库租赁的优先顺序。同时，监管机构持有的各种数据(如NSTA国家数据存储库)涉及遗留油井、其完整性和相关的地质属性。这些数据可以帮助评估苏格兰海床上遗留油井对天然气储存围堵构成的风险，但迄今尚未在这种情况下利用这些油井。这项博士研究将包括评估现有的遗留油井风险筛选方法和战略，评估与苏格兰近海环境相关的数据可用性，重点是遗留油井，整理所述数据，并开发可用于辅助风险筛选的定制数据库。随后，学生将进行数据分析，以更好地了解与封堵损失和遗留油井相关的关键风险因素，开发风险筛选方法，并将其应用于CES租赁区内的遗留油井，以帮助决策。

Carbon capture and storage (CCS) will play a vital role in mitigating greenhouse gas emissions and combating climate change during global efforts to reach NetZero. Offshore storage of CO2 presents a promising solution for long-term storage; however, it is crucial to assess, manage and mitigate the risks associated with the loss of containment at offshore CO2 storage facilities. The UK Continental Shelf is estimated to have a storage capacity of 80-90GT of CO2 (ETI UKSAP, 2011). Crown Estates Scotland (CES) are responsible for leasing assets for gas storage between 12 to 200 miles from the Scottish coast, an area of seabed that has a history of extensive oil and gas exploration and production, whereby more than 7,000 wells have been drilled since the late 1960s. The seabed available for potential gas storage managed by CES is approximately 7500 km2 in area and spans the Scottish coastline. When selecting optimal sites to lease for gas storage in any region, it is crucial to consider risk factors that may lead to loss of containment and evaluate the severity of consequences were containment to be compromised. Such risk screening exercises are critical to identify optimal areas for gas storage, to screen out areas with greater risk and to be used in the process of risk-based decision-making. Factors that determine the overall risk profile for an offshore storage area include geologic integrity and architecture, legacy infrastructure and integrity, seabed stability and the presence and nature of any environmental receptors that may be impacted by loss of containment. Of particular concern are legacy wells and their integrity for which many thousands exist within the Scottish offshore environment. Legacy wells are a major risk to containment during offshore geological storage, where integrity may become compromised allowing fugitive gas migration towards the seabed and into the marine environment. Currently, no legacy well risk screening tools, methods, or strategies specific to the Scottish offshore environment exist that can help manage, optimize and prioritize leasing of offshore gas storage in Scotland. Meanwhile, various data held by regulatory authorities (e.g., the NSTA National Data Repository) relate to legacy wells, their integrity and associated geological attributes. Such data could aid in assessment of risk posed to gas storage containment by legacy wells across the Scottish seabed, yet to date has not been utilized in such context. This PhD research will involve evaluating existing legacy well risk screening methods and strategies, appraising data availability related to the offshore Scottish environment with focus on legacy wells, collating said data and developing a custom database that can be used to aid in risk screening. Subsequently, the student will perform data analyses to better understand key risk factors associated with loss of containment and legacy wells, develop a risk screening approach, and apply it to legacy wells present within CES lease areas to aid in decision-making.