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

碳捕获与封存（CCS）已成为降低化石燃料燃烧产生的二氧化碳排放的一种有前景的手段。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二氧化碳的泄漏，也没有一种可行的方法来确定其所有权。这意味着，在多个操作人员注入的储存库发生泄漏的情况下，无法确定是谁的二氧化碳在泄漏。正在进行的关于泄漏和如何检测它的辩论已经经常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，特别是在拟议的储存地点附近，导致几个大型储存项目被取消，如荷兰巴伦德雷支的项目。减少公众对CCS的恐惧的一个方法是展示一种简单的方法，这种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。对稀有气体（氦、氖、氩、氪和氙）的测量，以及在天然二氧化碳场中碳和氧的轻、重稳定同位素的比例，显示了二氧化碳是如何自然储存数百万年的。惰性气体也被证明在识别亚利桑那州的一个二氧化碳储存库和怀俄明州的一个油田上的二氧化碳自然泄漏以及排除加拿大韦伯恩储存库的二氧化碳泄漏方面是有效的。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。这种富集是由于较重的惰性气体的溶解度较大，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烃源岩中，重惰性气体也有类似的富集，氦浓度也很高。由于惰性气体不具有反应性，因此这些富集物不会受到发电厂燃烧气体或煤的影响，因此将被传递到烟道气中。从法国Lacq的一个含氧燃料试点二氧化碳捕集厂获得的二氧化碳样本证实了这一点，其中含有远高于大气值的氦和氪富集物。尽管发现了这些独特的指纹，但目前还没有研究调查它们与不同的二氧化碳捕获技术或燃烧的化石燃料之间是否存在关联。我们建议在捕集后、捕集前和氧燃料中试工厂捕获的二氧化碳中测量碳、氧稳定同位素和稀有气体指纹。我们将查明是否由于使用的捕获技术或燃烧的燃料而产生独特的指纹。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，就可以在不需要增加人工示踪剂的情况下追踪二氧化碳。我们将调查它们是否足以区分注入同一储存地点的多个二氧化碳流的所有权，以及它们是否能够提供储存地点计划外的二氧化碳移动的早期预警。为了做到这一点，我们将确定从边界水坝发电厂捕获的二氧化碳的指纹，然后将其注入加拿大萨斯喀彻温省的aquisstore盐水含水层储存地点。通过将其与aquestore监测井（距注入井约100米）产生的二氧化碳指纹进行比较，我们将能够看到在二氧化碳穿过含盐含水层后指纹是否保留下来。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运动，特别是近海咸水层，这将用于未来英国的大量二氧化碳储存。

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.