Microanalysis of natural and engineered CO2 mineralisation at CarbFix2 site, Iceland

二氧化碳捕获和封存(CCS)是唯一一种可以直接减少化石燃料燃烧或工业过程排放所产生的二氧化碳排放的工业规模技术。考虑到全球能源和工业制造需求对化石燃料的依赖，CCS是全球实现二氧化碳净零排放的关键技术4。地质二氧化碳储存的成功与否，关键取决于储存点的长期安全。沉积储集层中储存的浮力气相CO2需要长时间的储存监测。或者，可以通过将注入的二氧化碳永久转化为储存点内的新的碳酸盐矿物来保证安全的储存。最近对二氧化碳注入反应性玄武岩时发生的封存进行了几次测试，特别是位于冰岛Hellisheidi地热田的CarbFix1项目[1]。对溶解的无机碳和注入二氧化碳的示踪剂的测量表明，注入的二氧化碳的95%(175吨)在两年内实现了矿化1。然而，该方法在工业规模上的可行性仍然不确定，因为关键问题是可行的注入性能保持多久是未知的。为了解决这个问题，CarbFix2实验于2014年启动，目前每年有10,000吨二氧化碳和5,000吨硫化氢被注入地热领域[2]关键研究问题：-根据钻井期间的观察和雷克雅未克能源公司的示踪测试，确定注入之前油田中发生了自然二氧化碳矿化的地方。-使用世界级的微束分析和地球化学建模解决单个晶体生长过程中自然二氧化碳沉淀发生的条件。-在工程注入二氧化碳和硫化氢之前建立基线地球化学指纹-从井下样品中识别CarbFix1碳酸盐的同位素特征。-进行实地考察，以暴露天然类似物的表面。在意大利利古里亚，经过充分研究的侏罗纪蛇绿岩杂岩含有碳酸盐矿化海底的黑云母，它们提供了空间信息，并制约了矿化路径和地球化学指纹随时间的保存。-通过实验再现了井下切割样品的矿化过程，并用同步加速器X射线显微照相术对其进行了成像。通过这些实验，矿物的溶解和再沉淀将被绘制并量化。-改变温度和盐度的4D显微断层成像实验将评估是否可以通过有目的地将策略注入到改变了盐水盐度的水库的较热或较冷部分来增强二氧化碳的矿化作用。方法和时间表：该项目将利用地球科学学院内的世界级离子微探针(SIMS)仪器(Cameca 1270和新Cameca IMS7f-Geo)。你将从钻孔岩屑和矿化玄武岩岩心样本中进行微观分析遍历单个晶体。每个晶体内的微米生长区，就像树上的年轮一样，记录了晶体生长过程中孔隙水的同位素和微量元素特征。将重建天然碳酸盐的生长持续时间、温度、二氧化碳和水来源。这些分析将得到一种新型x射线透明反应池中的矿化实验的补充，该反应池允许使用时间分辨同步x射线显微断层成像来监测流体-岩石相互作用。这将使用井下岩屑样本来直接测绘和量化矿物质在储层条件下的溶解和再沉淀[3]。所产生的知识将被用来确定如何通过不同的注入策略来增强二氧化碳矿化，并告知如何将这种控制准确地纳入该储层的二氧化碳矿化预测模型中。

CO2 capture and storage (CCS) is the only industrial scale technology that can directly reduce the CO2 emissions produced by the combustion of fossil fuels or industrial process emissions. Given global reliance on fossil fuels for energy and industrial manufacturing needs, CCS is an essential technology for the global drive to reach net zero CO2 emissions to the atmosphere4. The success of geologic CO2 storage critically depends on the long-term security of the storage site. Buoyant gas phase CO2 stored in sedimentary reservoirs requires long duration monitoring of storage. Alternatively, secure storage can be guaranteed through the permanent conversion of injected CO2 into new carbonate minerals within the storage site.Several tests of the sequestration that occurs when CO2 is injected into reactive basalts have recently been undertaken, notably the CarbFix1 project, located at the Hellisheidi geothermal field in Iceland[1]. Measurements of dissolved inorganic carbon and tracers injected with the CO2 indicate that mineralisation of >95 % of the injected CO2 (175 tonnes) was achieved within two years1. However, feasibility of the method at an industrial scale is still uncertain, as the key question of how long viable injectivity can be maintained is unknown. To address this question, the CarbFix2 experiment was launched in 2014, and currently 10,000 tonnes of CO2 and 5,000 tonnes of H2S are being injected per year into the geothermal field[2]Key research questions:-Identify where natural CO2 mineralisation has occurred in the field prior to injection based on observations made during drilling and tracer tests by Reykjavik Energy.-Resolve the conditions under which natural CO2 precipitation took place during growth of individual crystals using world-class microbeam analysis and geochemical modelling.-Establish baseline geochemical fingerprints prior to engineered injection of CO2 and H2S-Identify isotopic signatures of CarbFix1 carbonates from downhole samples.-Undertake field visit to surface exposures of natural analogues. Well-studied Jurassic ophiolite complexes in Liguria (Italy) host ophicalcites of carbonate mineralised ocean floor, which provide spatial information and constraints on the preservation of mineralisation pathways and geochemical fingerprints over time.-Reproduce the mineralization process on downhole cutting samples experimentally and image it with synchrotron-based X-ray microtomograph. From these experiments, dissolution and re-precipitation of minerals will be mapped and quantified.-4D microtomography experiments, varying temperature and salinity, will assess if CO2 mineralisation can be enhanced through purposeful injection strategies into hotter or colder parts of the reservoir with changed brine salinity.Methodology and timetable:This project will utilise the world-class ion microprobe (SIMS) instruments within the School of GeoSciences (Cameca 1270 and new Cameca IMS 7f-geo). You will make micro-analytical traverses across individual crystals from borehole cuttings and from mineralised basalt core samples. The micrometre growth zones within each crystal, like the rings on a tree, record the isotope and trace element signatures of porewater during the crystal growth. The growth duration, temperature, CO2 and water origins of natural carbonates will be reconstructed.These analyses will be complemented by mineralisation experiments in a novel x-ray transparent reaction cell that allows monitoring fluid-rock interaction with time-resolved synchrotron x-ray microtomography. These will use downhole cuttings samples to directly map and quantify dissolution and re-precipitation of minerals at reservoir conditions[3]. The knowledge generated will be used to ascertain how CO2 mineralisation can be enhanced through varied injection strategies and inform how to accurately incorporate such controls into predictive models of CO2 mineralisation in this reservoir.