Solubility trapping of CO2 in deep saline aquifers

碳捕获和封存是全球面临的主要挑战之一。将二氧化碳（CO2）长期储存在地下深处的含盐含水层中是一个关键的机会，它提供了在减少排放的同时持续获取加拿大油砂等化石燃料的可能性。然而，在实施之前，需要解决二氧化碳泄漏的相关风险，以确保储存的安全性。这就需要开发工具来评估所涉及的所有因素。二氧化碳的储存有几种机制。这些作用包括溶解在盐水中，以残余物的形式或通过矿化被困在储集岩中。然而，在这些机制如何促成和影响二氧化碳的长期（世纪到千年的时间尺度）命运方面，还存在知识缺口。此外，这些地下水库的储水量是不确定的。***研究表明，假设所有孔隙水都被二氧化碳饱和，阿尔伯塔盆地非常适合二氧化碳储存，其溶解能力为4000亿吨，这是不可能的。我们最近的研究表明，在短期内（~30年），只有8%的二氧化碳可以被捕获在盐水中。其余的可能留在自由相，这是容易泄漏的。然而，诸如对流溶解之类的长期机制可能会增加这一极限并降低泄漏的风险。***注入深层含盐含水层的二氧化碳密度低于常驻盐水。在密度对比的驱动下，它会以自由相的形式在密封岩石下扩散，同时存在泄漏的危险。然而，二氧化碳会慢慢溶解到下面的盐水中。由此产生的二氧化碳饱和盐水的密度略高于原有的盐水，使它们下沉到含水层的底部。通过不断下沉饱和CO2的卤水以及新鲜卤水自下而上的向上流动来增强CO2的溶解，减少了自由相CO2的体积，从而降低了泄漏的风险。主要的一点是，一旦二氧化碳沉降到含水层底部，它就不能轻易向上迁移，它可能会以最小的泄漏风险被保留下来。因此，溶解度捕获可以实现安全存储。***该研究计划扩展了我们的知识，并通过执行有助于确保和安全实施地理存储的研究提供了所需的方法。目前，利用油藏模型对溶蚀圈闭进行大规模建模是一个巨大的挑战，并且需要昂贵的计算资源和时间。因此，需要能够在地质尺度上准确模拟这一过程的高效模型。特别是，尺度定律，可以纳入油藏模拟，是非常重要的，将是一个关键的和新颖的贡献。拟议的研究将为将新公式纳入数值油藏模拟器提供一个场所，从而实现计算成本更低、效率更高的现场规模模拟

Carbon capture and storage is one of the major global challenges. Long-term storage of carbon dioxide (CO2) in deep underground saline aquifers is a key opportunity that offers the possibility of sustaining access to fossil fuels such as oil sands in Canada while reducing emissions. However, prior to implementation, associated risks of CO2 leakage need to be addressed to ensure safety of storage. This requires development of tools in order to assess all the factors involved.***CO2 storage takes place by several mechanisms. These include dissolution in brines, trapping in the reservoir rocks in form of residual or through mineralization. However, there is a knowledge gap in how these mechanisms contribute to and affect the long-term (century-to-millennium time scales) fate of CO2. Also, the storage capacity of these underground reservoirs is uncertain.***Studies have shown that the Alberta basin is well suited for CO2 storage with a dissolution capacity of 4000 gigatons assuming that all the pore water could become saturated with CO2, which is not likely. Our recent studies have shown that in the short-term (~30 years) only 8% of CO2 can be trapped in brines. The rest may remain in the free phase, which is prone to leakage. However, long-term mechanisms such as convective dissolution may increase this limit and reduce the risk of leakage.***The injected CO2 in deep saline aquifers is less dense than the resident brines. Driven by density contrast, it will spread under a sealing rock as a free phase while there is risk of leakage. However, CO2 slowly dissolves into the underlying brines. The resulting CO2-saturated brines are slightly denser than resident ones, making them sink to the bottom of the aquifer. Enhanced dissolution of CO2 by continuous sinking of CO2-saturated brines as well as upward flow of fresh brine from bottom to the top reduces the volume of the free phase CO2 and thus reduces the risk of leakage. The main point is that once CO2 sinks to the bottom of the aquifer, it cannot migrate upwards easily and it may be retained with minimal risk of leakage. Therefore, dissolution trapping could enable secure storage.***This research program expands our knowledge and provides required methodologies by performing studies that help secure and safe implementation of geostorage. Currently, large-scale modeling of dissolution trapping using reservoir models poses a great challenge and requires prohibitively expensive computational resources and time. Therefore, efficient models that can accurately simulate the process at geological scale are required. In particular, scaling laws, which can be incorporated into reservoir simulators, are of great importance and will be a key and novel contribution of this proposal. The proposed research will provide a venue for incorporation of new formulations into numerical reservoir simulators leading to a computationally less expensive and efficient field scale simulations.**