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

碳捕获和封存(CCS)已成为降低化石燃料燃烧产生的二氧化碳排放量的一种很有前途的手段。然而，对有害二氧化碳泄漏可能性的担忧正在导致该技术的广泛采用缓慢。到目前为止，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的泄漏，或者找出一种可行的方法来确定其所有权。这意味着，在多个操作员注入的储存地点发生泄漏的情况下，无法确定是谁在泄漏二氧化碳。大众媒体和科学出版物经常记录正在进行的关于渗漏以及如何发现渗漏的辩论。这造成了公众的困惑和恐惧，特别是在拟建的储存地点附近，导致几个大型储存项目被取消，例如荷兰的Barendrecht。减少公众对CCS的担忧的方法之一是展示一种简单的方法，能够可靠地检测储存地点的二氧化碳泄漏并确定二氧化碳的所有权。对天然二氧化碳气田中惰性气体(氦、氦、氩、氪和氙气)以及碳和氧的轻、重稳定同位素比率的测量表明，二氧化碳是如何在数百万年后自然储存的。稀有气体还被证明可以有效地识别亚利桑那州二氧化碳储存库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点二氧化碳泄漏的可能性。最近的研究表明，相对于从巴西一家硝酸盐化肥厂捕获的二氧化碳中的氩和氦，氪的含量有所增加。这种浓缩是由于较重的稀有气体具有更大的溶解度，因此它们更容易溶解在用于捕获的溶剂中。这种指纹已被证明是追踪注入巴西和美国油田的二氧化碳以增加石油产量的有效手段。在煤、煤层气和富含有机油气的源岩中，类似的重惰性气体浓缩以及高氦浓度都有很好的记录。由于惰性气体是不反应的，这些浓缩不会受到发电厂燃烧天然气或煤的影响，因此会被传递到烟道气中。从法国Lacq的氧气燃料二氧化碳捕集试点工厂获得的二氧化碳样本证实了这一点，这些二氧化碳样本含有远高于大气值的氦和氪。尽管对这些独特的指纹进行了鉴定，但尚未有研究调查它们是否与不同的二氧化碳捕获技术或正在燃烧的化石燃料之间存在关联。我们建议测量碳和氧稳定同位素和惰性气体指纹从后，前和氧气燃料中试捕集工厂捕获的二氧化碳。我们将找出是使用的捕获技术还是燃烧的燃料产生了独特的指纹。我们将确定这些指纹是否足够独特，一旦二氧化碳被注入地下，就可以追踪它，而不需要增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储存点的多个二氧化碳气流的所有权，以及它们是否能为二氧化碳意外移出储存点提供早期预警。为此，我们将在将其注入加拿大萨斯喀彻温省的Aquistore咸水含水层储存点之前，确定从边界大坝发电厂捕获的二氧化碳指纹。通过将其与Aquistore监测井产生的二氧化碳指纹进行比较，我们将能够看到二氧化碳在穿过盐渍含水层后是否保留了指纹。这将表明这项技术是否可以用于跟踪未来工程储存地点的二氧化碳移动，特别是将用于未来英国大容量二氧化碳储存的离岸咸水含水层。

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.