Migration of CO2 through North Sea Geological Carbon Storage Sites: Impact of Faults, Geological Heterogeneities and Dissolution

CO2的深部地质封存是减少人为CO2排放的主要技术手段之一。该过程需要在源头（例如燃煤电厂）捕获CO2，将CO2输送到注入地点，并将液化CO2泵入千米深的多孔储层中，这些储层通常最初在盐水或先前包含的石油或天然气中饱和。最初，漂浮的CO2倾向于通过多孔储层上升，直到它被不可渗透的层位捕获，就像石油或天然气被捕获了几千年一样。随后，通过将CO2溶解到水中（碳酸水比非碳酸水更致密并且会下沉），或者通过毛细管力作用以将CO2保持在孔隙空间的小范围内，可以更安全地捕获漂浮的CO2。因此，通过这些捕集过程降低了通过覆盖层迁移的浮力CO2的任何风险。限制实际地质覆盖层中的溶解速率和毛细管捕获速率是量化和减少渗漏风险的战略的关键组成部分。英国在地质上处于实施海上CO2封存的有利位置，北海有许多潜在的储层。该提案将通过量化北海储层覆盖层典型的断层和非均质地层中的捕获率，以及量化我们在覆盖层中地震检测任何CO2的能力，提高我们对覆盖层泄漏风险的理解。二氧化碳的粘性比水小，并且会沿沿着更强的层指状移动。沉积地层在所有尺度上的渗透率都有很大的变化，这将大大增加CO2溶解在地层沃茨中的速率。该分析在范围和所得技术方面具有普遍性，但适用于Goldeneye油田，该油田是CO2储存的目标，也是政府CCS商业化竞争的候选者。我们的方法是从地质学角度研究覆盖层内的相关地质异质性，并绘制该地区断层内流体流动的结构和倾向。岩芯提供岩石样本（5x 20 cm），然后可以在实验室中进行询问。我们将直接成像，在典型的条件下的覆盖层，流体流动，溶解和毛细管捕获的速度都在规模的个别孔隙内的岩石（微米）和整个长度的核心（厘米）。流体的地球化学分析将使我们能够在岩心驱替实验中测量原位溶解和沉淀速率。为了确定如何在储层和覆盖层的尺度上应用流速和圈闭，必须根据通过1-100厘米尺度地质非均质性和沿着断层的流动来解释结果。为了评估非均质性对捕获率的影响，我们将构建简化模型的流量沿着主要分层地层，或沿着横切故障，沿着与实验室模拟实验，我们可以光学评估捕获率，从而为我们的预测提供了一个坚实的基准。最后，在更大的尺度上，我们将在现有的CO2实验（如Sleipner在北海）的烟囱结构的图像流，从而提供定量估计我们的地震解决泄漏途径的存储覆盖层的能力。我们的建议将开发所需的工具，以地质上覆盖层的北海，提供定量估计的捕获率在地质复杂的覆盖层和断层复合体，并证明地震解决流体流动路径的能力。迄今为止，已在相对安全的储存地点证明了CO2的地质储存。这项工作将通过量化与地质情况较为复杂的封存地点的渗漏相关的潜在风险，大大扩大二氧化碳地质封存的潜力。

The storage of CO2 in deep geological formations is one of the chief technological means of reducing anthropogenic emissions of CO2 to the atmosphere. The process requires capturing CO2 at source (e.g. coal-fired power plants), transporting CO2 to the injection site, and pumping liquefied CO2 into kilometre deep, porous reservoirs that are typically initially saturated in saline water or previously contained oil or gas. Initially, buoyant CO2 tends to rise through the porous reservoir until it is trapped by an impermeable horizon, in the same way that oil or gas has been trapped over millennia. Subsequently, buoyant CO2 may be more securely trapped by dissolving CO2 into water (carbonated water is more dense than non-carbonated water and will sink), or by capillary forces acting to hold the CO2 in the small confines of the pore space. Any risk of buoyant CO2 migrating through the overburden is therefore reduced by these trapping processes. Constraining the rates of dissolution and capillary trapping in realistic geological overburden is a key component of strategies to quantify and reduce the risks of leakage. The UK is geologically well placed to implement offshore CO2 storage, with many potential reservoirs in the North Sea.This proposal will improve our understanding of the risks of leakage through the overburden by quantifying trapping rates in faults and heterogeneous strata typical of the overburden of North Sea reservoirs, and by quantifying our ability to seismically detect any CO2 in the overburden. CO2 is less viscous than water and will finger along more permeable layers. Sedimentary strata exhibit large variations in permeability on all scales that will substantially increase the rates at which CO2 dissolves in the formation waters.The analysis, while general in scope and resultant techniques, is applied to the Goldeneye field, a target for CO2 storage and a candidate for the Government's CCS commercialisation competition. Our approach is to geologically characterise the relevant geological heterogeneity within the overburden, and to map the structure and propensity for fluid flow within faults in that locality. Drill core provides samples of rock (5x20 cm) that can then be interrogated in the laboratory. We will directly image, at conditions typical of the overburden, the rates of fluid flow, dissolution, and capillary trapping both at the scale of individual pores within the rock (microns) and over the length of the core (centimetres). Geochemical analysis of the fluids will allow us to measure in situ dissolution and precipitation rates in our core flooding experiments. In order to determine how rates of flow and trapping may be applied at the scale of the reservoir and overburden the results must be interpreted in light of flow through 1-100 centimetre scale geological heterogeneities and along faults. To assess the impact of heterogeneities on the rates of trapping we will construct simplified models of flow along predominantly layered strata, or along cross-cutting faults, along with laboratory analogue experiments in which we can optically assess trapping rates and thereby provide a firm benchmark for our predictions. Finally, at larger scales, we will image flow up chimney structures in existing CO2 experiments (eg Sleipner in the North Sea) and thus provide quantitative estimates of our ability to seismically resolve leakage pathways in the storage overburden. Our proposal will develop tools needed to geologically characterise the North Sea overburden, provide quantitative estimates of trapping rates in geologically complex overburden and fault complexes, and demonstrate the ability to seismically resolve fluid flow pathways. To date geological CO2 storage has been demonstrated at relatively safe storage sites. This work would greatly expand the potential for geological CO2 storage by quantifying the potential risks associated with leakage in more geologically complex storage sites.