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

包括化石燃料发电在内的工业二氧化碳排放被认为是全球气候变化和海洋酸化的可能因素，但大多数经济体在未来几十年仍将依赖这些技术。二氧化碳捕获和储存（CCS）已被确定为减少大气中二氧化碳排放量的重要途径。CCS被认为是到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上升控制在2摄氏度以下的关键贡献，正如欧盟委员会政策所概述的那样。此外，CCS被认为是减少继续使用化石燃料的缓解措施成本的一个重要途径。在枯竭的油气藏和盐水层中离岸储存二氧化碳是大多数欧洲国家的选择，目前有一个运作中的储存综合体（挪威Sleipner），其他几个商业规模的示范项目正处于开发的后期阶段（例如ROAD-荷兰、彼得黑德和白色玫瑰-英国），预计到2020年将全面运作。海上CCS的一个关键要素是，有信心了解任何泄漏的风险。海底任何可能的CO2泄漏的位置和潜在强度在很大程度上取决于储存CO2的储层上覆岩石中流体（溶解和气态CO2）通道的分布情况，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洋沉积岩结构的研究表明，类似烟囱或管道的近垂直结构横切沉积序列。这些结构可以是用于流体流动的路径。在地质时期的某个时候，来自更深岩层的天然流体已经通过这些结构迁移。如果从海底下储存库泄漏的二氧化碳到达这些结构的底部，并且如果它们的渗透性足够高，它们可能成为二氧化碳泄漏到海底和上覆水柱的通道。为了提供一个可靠的预测潜在的海底渗漏的网站，这些途径的连续性，特别是他们的渗透性需要更好地理解。在这个项目（CHIMNEY）中，我们将收集新的数据，在北海烟囱结构，使用一艘船，使新的和不寻常的测量声波。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，并记录海底仪器（称为海底地震仪）的声音到达。通过从一系列方向和频率观察通过地下的声音传播路径，我们将获得有关烟囱以及周围岩石中的裂缝/流体路径的信息。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。通过了解声音通过具有已知流体路径的合成岩石的传播，我们可以理解海洋实验的结果。我们还将钻入烟囱，收集岩心样本，进行岩心地质和流体化学分析。地下烟囱的计算机模型将结合地震实验，岩石物理和化学的结果。我们将与参与CCS的公司合作，建立现实的流体流动计算机模型，告诉我们通常在北海范围内与二氧化碳捕获和储存相关的烟囱结构泄漏的风险。

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 risk of leakage from chimney structures generally within the North Sea that are relevant to Carbon Dioxide Capture and Storage.