Geochemical tracers for monitoring offshore CO2 stores
Geochemical tracers for monitoring offshore CO2 stores
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DOI：
10.1016/j.ijggc.2017.07.021
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发表时间：
2017-10
影响因子：
3.9
通讯作者：
J. Roberts;S. Gilfillan;L. Stalker;M. Naylor
中科院分区：
文献类型：
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作者：
J. Roberts;S. Gilfillan;L. Stalker;M. Naylor
化学示踪剂被认为是检测、归因和量化从地质二氧化碳封存地点泄漏到地表的任何二氧化碳的有效手段，而地质二氧化碳封存地点是碳捕获和封存（CCS）技术的关键组成部分。全球二氧化碳封存能力的很大一部分位于海上，世界上一些地区没有陆上存储。为了向监管机构和公众保证二氧化碳封存的完整性，必须证明强大的海上监测系统已经到位。一系列泄漏化学示踪剂已在全球陆上 CCS 试点项目中进行了测试，但迄今为止，尚未在海上注入项目或二氧化碳释放实验中进行过试验。在此，我们首次批判性地回顾了围绕海上 CCS 项目示踪剂商业规模使用的当前问题，并研究了海洋环境带来的限制和成本影响。这些限制包括海上示踪剂采样的物流、示踪剂在海洋环境中的命运、示踪剂背景水平、海洋毒性和立法障碍——特别关注欧洲和英国。显然，形成二氧化碳流天然成分的化学品是优选的示踪剂，因为易于许可并避免采购和人为添加示踪剂的成本和风险。然而，添加的示踪剂因其独特的成分以及控制和调节浓度的能力而提供了更高的可靠性。我们确定氦和氙同位素（特别是 124,129Xe）以及人工示踪剂（例如 PFC 和氘化甲烷）作为最合适的添加示踪剂。这是由于它们的行为保守、对环境影响较小且相对便宜。重要的是，我们还发现，由于环境问题，SF6 和 C14 并不是 CCS 的可行示踪剂，并且可以基于成本排除许多其他潜在的示踪剂。此外，我们还确定了使用示踪剂进行海上监测所特有的关键挑战，并强调了未来工作应解决的关键不确定性。这些包括示踪剂化合物在上覆层上升过程中可能的吸附或扩散、示踪剂在 CCS 监测相关时间范围内的寿命、示踪剂泄漏对环境的允许影响以及示踪剂在海底 CO2 气泡流和溶解的 CO2 中的行为。这些不确定性直接影响适当示踪剂的选择、可靠检测所需的注射程序和浓度以及适当的采样方法。因此，海上示踪剂的选择和相关费用目前受到很大限制。此外，在海洋环境中进行示踪剂采样的经验有限；目前的方法成本高昂，必须加以简化，以实现负担得起的监测战略。有必要开展进一步的工作来解决这些未知问题，以便评估用于二氧化碳泄漏定量的潜在示踪剂的性能，并为有效的海上示踪剂监测计划提供更准确的成本计算。
Chemical tracers are proposed as an effective means of detecting, attributing and quantifying any CO2leaks to surface from geological CO2storage sites, a key component of Carbon Capture and Storage (CCS) technology. A significant proportion of global CO2storage capacity is located offshore, with some regions of the world having no onshore stores. To assure regulatory bodies and the public of CO2storage integrity it is important to demonstrate that robust offshore monitoring systems are in place. A range of chemical tracers for leakage have been tested at onshore pilot CCS projects worldwide, but to date they have not been trialled at injection projects or CO2release experiments located offshore. Here, for the first time, we critically review the current issues surrounding commercial scale use of tracers for offshore CCS projects, and examine the constraints and cost implications posed by the marine environment. These constraints include the logistics of sampling for tracers offshore, the fate of tracers in marine environments, tracer background levels, marine toxicity and legislative barriers – with particular focus on the Europe and the UK. It is clear that chemicals that form a natural component of the CO2stream are preferable tracers for ease of permitting and avoiding cost and risks of procuring and artificially adding a tracer. However, added tracers offer more reliability in terms of their unique composition and the ability to control and regulate concentrations. We identify helium and xenon isotopes (particularly124,129Xe), and artificial tracers such as PFCs and deuterated methane as the most suitable added tracers. This is due to their conservative behaviour, low environmental impact and relative inexpense. Importantly, we also find that SF6and C14are not viable tracers for CCS due to environmental concerns, and many other potential tracers can be ruled out on the basis of cost. Further, we identify key challenges that are unique to using tracers for offshore monitoring, and highlight critical uncertainties that future work should address. These include possible adsorption or dispersion of tracer compounds during ascent through the overburden, longevity of tracers over the timeframes relevant for CCS monitoring, the permissible environmental effects of tracer leakage, and tracer behaviour in seabed CO2bubble streams and in dissolved CO2. These uncertainties directly affect the selection of appropriate tracers, the injection program and concentrations necessary for their reliable detection, and appropriate sampling approaches. Hence offshore tracer selection and associated expense are currently poorly constrained. Further, there is limited experience of sampling for tracers in the marine environment; current approaches are expensive and must be streamlined to enable affordable monitoring strategies. Further work is necessary to address these unknowns so as to evaluate the performance of potential tracers for CO2leak quantitation and provide more accurate costings for effective offshore tracer monitoring programs.