Fingerprinting captured CO2 using natural tracers: Determining CO2 fate and proving ownership

碳捕获与封存（CCS）已成为减少化石燃料燃烧二氧化碳排放的一种有前景的方法。然而，对有害二氧化碳泄漏可能性的担忧导致该技术的广泛采用缓慢。迄今为止的研究未能找到一种廉价而有效的方法来明确识别注入的二氧化碳泄漏，也未能找到一种可行的方法来识别其所有权。这意味着，如果多个运营商注入的储存地点发生泄漏，则无法确定谁的二氧化碳泄漏。关于泄漏以及如何检测泄漏的持续争论已频繁地记录在大众媒体和科学出版物中。这引起了公众的困惑和恐惧，特别是在拟定封存地点附近，导致多个大型封存项目被取消，例如荷兰巴伦德雷赫特的封存项目。减少公众对 CCS 恐惧的一种方法是展示一种简单的方法，能够可靠地检测封存地点二氧化碳的泄漏并确定二氧化碳的所有权。对天然二氧化碳气田中稀有气体（氦、氖、氩、氪和氙）以及碳和氧的轻稳定同位素和重稳定同位素的比率的测量显示了二氧化碳是如何自然储存数百万年的。事实证明，稀有气体还可以有效识别亚利桑那州二氧化碳储层和怀俄明州油田上方二氧化碳的自然泄漏，并排除加拿大韦伯恩储存地点所谓的二氧化碳泄漏。最近的研究表明，巴西硝酸盐化肥厂捕获的二氧化碳中，氪的含量相对于氩和氦的含量有所增加。这种富集是由于较重的惰性气体的溶解度更大，因此它们更容易溶解到用于捕获的溶剂中。该指纹已被证明是跟踪注入巴西和美国油田以增加石油产量的二氧化碳的有效手段。煤炭、煤层气和富含有机物的油气源岩中也有类似的重惰性气体富集以及高氦浓度的记录。由于稀有气体不发生反应，因此这些富集不会受到发电厂中燃烧天然气或煤炭的影响，因此将被传递到烟道气中。从法国拉克的富氧燃料试点二氧化碳捕集工厂获得的二氧化碳样本证实了这一点，其中氦和氪的浓度远高于大气值。尽管识别了这些独特的指纹，但尚未研究它们与不同的二氧化碳捕集技术或燃烧的化石燃料之间是否存在相关性。我们建议测量从后、前和富氧燃料中试捕集工厂捕集的二氧化碳中的碳和氧稳定同位素和稀有气体指纹。我们将查明独特的指纹是否来自所使用的捕获技术或燃烧的燃料。我们将确定这些指纹是否足够独特，可以在二氧化碳注入地下后追踪二氧化碳，而无需添加昂贵的人工示踪剂。我们将调查它们是否足以区分注入同一封存地点的多个二氧化碳流的所有权，以及它们是否能够对二氧化碳从封存地点意外移出的早期预警。为此，我们将确定从边界大坝发电厂捕获的二氧化碳在注入加拿大萨斯喀彻温省 Aquistore 咸水层封存地点之前的指纹。通过将其与距注入井约 100m 的 Aquistore 监测井产生的 CO2 指纹进行比较，我们将能够了解 CO2 穿过咸水层后是否保留了指纹。这将表明该技术是否可用于跟踪未来工程封存地点中二氧化碳的移动，特别是海上咸水含水层，该含水层将用于未来英国的大量二氧化碳封存。

Carbon capture and storage (CCS) has emerged as a promising means of lowering CO2 emissions from fossil fuel combustion. However, concerns about the possibility of harmful CO2 leakage are contributing to slow widespread adoption of the technology. Research to date has failed to identify a cheap and effective means of unambiguously identifying leakage of CO2 injected, or a viable means of identifying ownership of it. This means that in the event of a leak from a storage site that multiple operators have injected into, it is impossible to determine whose CO2 is leaking. The on-going debate regarding leakage and how to detect it has been frequently documented in the popular press and scientific publications. This has contributed to public confusion and fear, particularly close to proposed storage sites, causing the cancellation of several large storage projects such as that at Barendrecht in the Netherlands.One means to reduce public fears over CCS is to demonstrate a simple method which is able to reliably detect the leakage of CO2 from a storage site and determine the ownership of that CO2. Measurements of noble gases (helium, neon, argon, krypton and xenon) and the ratios of light and heavy stable isotopes of carbon and oxygen in natural CO2 fields have shown how CO2 is naturally stored over millions of years. Noble gases have also proved to be effective at identifying the natural leakage of CO2 above a CO2 reservoir in Arizona and an oil field in Wyoming and in ruling out the alleged leakage of CO2 from the Weyburn storage site in Canada.Recent research has shown amounts of krypton are enhanced relative to those of argon and helium in CO2 captured from a nitrate fertiliser plant in Brazil. This enrichment is due to the greater solubility of the heavier noble gases, so they are more readily dissolved into the solvent used for capture. This fingerprint has been shown to act as an effective means of tracking CO2 injected into Brazilian and USA oil fields to increase oil production. Similar enrichments in heavy noble gases, along with high helium concentrations are well documented in coals, coal-bed methane and in organic rich oil and gas source rocks. As noble gases are unreactive, these enrichments will not be affected by burning the gas or coal in a power station and hence will be passed onto the flue gases. Samples of CO2 obtained from an oxyfuel pilot CO2 capture plant at Lacq in France which contain helium and krypton enrichments well above atmospheric values confirm this.Despite identification of these distinctive fingerprints, no study has yet investigated if there is a correlation between them and different CO2 capture technologies or the fossil fuel being burnt. We propose to measure the carbon and oxygen stable isotope and noble gas fingerprint in captured CO2 from post, pre and oxyfuel pilot capture plants. We will find out if unique fingerprints arise from the capture technology used or fuel being burnt. We will determine if these fingerprints are distinctive enough to track the CO2 once it is injected underground without the need of adding expense artificial tracers. We will investigate if they are sufficient to distinguish ownership of multiple CO2 streams injected into the same storage site and if they can provide an early warning of unplanned CO2 movement out of the storage site.To do this we will determine the fingerprint of CO2 captured from the Boundary Dam Power Plant prior to its injection into the Aquistore saline aquifer storage site in Saskatechwan, Canada. By comparing this to the fingerprint of the CO2 produced from the Aquistore monitoring well, some 100m from the injection well, we will be able to see if the fingerprint is retained after the CO2 has moved through the saline aquifer. This will show if this technique can be used to track the movement of CO2 in future engineered storage sites, particularly offshore saline aquifers which will be used for future UK large volume CO2 storage.