Characterization of major overburden leakage pathways above sub-seafloor CO2 storage reservoirs in the North Sea (CHIMNEY)

工业排放的二氧化碳（CO2），包括化石燃料发电，被认为是全球气候变化和海洋酸化的一个可能因素，但大多数经济体在未来几十年仍将依赖这些技术。二氧化碳捕集与封存（CCS）已被确定为减少大气中二氧化碳排放量的重要途径。正如欧盟委员会的政策所概述的那样，CCS被视为到2050年将人类温室气体排放量减少80-95%，并将气候变化导致的温度升高控制在2摄氏度以下的关键贡献。此外，CCS被认为是降低围绕继续使用化石燃料的缓解措施成本的重要途径。在枯竭的油气储层和含盐含水层中进行二氧化碳的海上储存是大多数欧洲国家的选择，目前有一个正在运行的储存综合设施（挪威的Sleipner），还有几个其他商业规模的示范项目处于开发的后期阶段（例如ROAD-Netherlands， Peterhead和White Rose-UK），预计到2020年将全面投入运营。海上CCS的一个关键因素是，人们有信心了解任何泄漏的风险。海底任何可能的二氧化碳泄漏的位置和潜在强度，在很大程度上取决于储存二氧化碳的储层上的岩石中流体（溶解和气态二氧化碳）通道的分布，以及这些通道传输流体的能力（称为渗透率）。最近对北海和挪威海海相沉积岩结构的研究表明，近乎垂直的结构，类似于烟囱或管道，横切了沉积序列。这些结构可能是流体流动的途径。在地质年代的某个时间点，来自较深岩层的天然流体通过这些构造迁移。如果从海底储层泄漏的二氧化碳到达这些结构的底部，如果它们的渗透性足够高，它们就可以作为二氧化碳泄漏到海底和上面的水柱的途径。为了对潜在的海底渗漏点提供可靠的预测，需要更好地了解这些途径的连续性程度，特别是它们的渗透性。在这个项目（烟囱）中，我们将通过一艘船收集北海烟囱结构上的新数据，用声波进行新的和不寻常的测量。我们将使用几种不同的海洋声源来制作烟囱的图像，使用海面上的接收器，并将声音记录在海底仪器上，即海底地震仪。通过观察从不同方向和频率穿过地下的声音传播路径，我们将获得有关烟囱中裂缝/流体路径以及周围岩石的信息。我们将使用模拟地下岩石的材料（合成岩石）的实验室研究来校准和理解我们的海洋地震结果。通过理解声音在具有已知流体路径的合成岩石中的传播，我们可以理解海洋实验的结果。我们还将钻入烟囱并收集岩心样本，我们将对岩心地质学和流体化学进行分析。结合地震实验、岩石物理和化学的结果，建立了地下烟囱的计算机模型。我们将与参与CCS的公司合作，建立流体流动的真实计算机模型，告诉我们北海烟囱结构泄漏的可能性，这与二氧化碳捕获和储存有关。

Industrial emissions of carbon dioxide (CO2), including fossil fuel power generation, are recognised as a likely agent of global climate change and acidification of the oceans, but most economies will remain dependent on these technologies for the next few decades. Carbon dioxide Capture and Storage (CCS) has been identified as an important way of reducing the amount of CO2 added to the atmosphere. CCS is seen as making a key contribution to reducing mankind's greenhouse gas emissions by 80-95% by 2050 and keeping climate change derived temperature increases below 2 degrees C, as outlined in European Commission policy. In addition, CCS is considered an important way of reducing the cost of mitigation measures around the continued use of fossil fuels. Offshore storage of CO2 in depleted oil and gas reservoirs and saline aquifers is the option of choice for most European nations, and there is currently one operational storage complex (Sleipner, Norway), and several other commercial scale demonstration projects are in late stages of development (e.g. ROAD-Netherlands, Peterhead and White Rose-UK), and expected to be in full operation by 2020. A key element of CCS offshore is that there is confidence that the risks of any leakage are understood. The location and potential intensity of any possible CO2 leakage at the seafloor are critically dependent on the distribution of fluid (dissolved and gaseous CO2) pathways in the rocks overlying the reservoirs in which the CO2 is stored, and on the ability of these pathways to transmit fluid (termed permeability). Recent studies of the structure of marine sedimentary rocks in the North and Norwegian Seas have revealed that near-vertical structures, which resemble chimneys or pipes, cross-cut the sedimentary sequence. These structures may be pathways for fluid flow. Natural fluids from deeper rock layers have migrated through these structures at some point in geological time. If CO2 leaking from sub-seafloor storage reservoirs reaches the base of these structures, and if their permeability is sufficiently high, they could act as CO2 leakage pathways towards the seafloor and overlying water column. To provide a reliable prediction of potential seafloor seep sites, the degree to which these pathways are continuous and especially their permeability needs to be better understood.In this project (CHIMNEY) we will collect new data over a chimney structure within the North Sea by using a ship to make new and unusual measurements with sound waves. We will use several different marine sound sources to make images of the chimney, using receivers at the sea surface, and also record the sound arrivals on sea bed instruments known as ocean bottom seismometers. By looking at the sound travel paths through the sub-surface from a range of directions and frequencies we will obtain information about fractures/fluid pathways in the chimney as well as the surrounding rocks. We will calibrate and understand our marine seismic results using laboratory studies of materials (synthetic rocks) that mimic the sub-surface rocks. By understanding the propagation of sound through synthetic rocks with known fluid pathways we can understand the results of the marine experiment. We will also drill into the chimney and collect core samples which we will analyse for core geology and fluid chemistry. A computer model of the sub-surface chimney will be constructed combining the results of the seismic experiment, rock physics, and chemistry. We will work with companies involved in CCS to build realistic computer models of fluid flow that tell us about the potential of leakage from chimney structures generally within the North Sea that are relevant to Carbon Dioxide Capture and Storage.