Sequestration of carbon dioxide in deep-sea sediments has been proposed for the long-term storage of anthropogenic CO₂ that can take advantage of the current offshore infrastructure. It benefits from the negative buoyancy effect and hydrate formation under conditions of high pressure and low temperature. However, the multiphysics process of injection and postinjection fate of CO₂ and the feasibility of subseabed disposal of CO₂ under different geological and operational conditions have not been well studied. With a detailed study of the coupled processes, we investigate whether storing CO₂ into deep-sea sediments is viable, efficient, and secure over the long term. We also study the evolution of multiphase and multicomponent flow and the impact of hydrate formation on storage efficiency. The results show that low buoyancy and high viscosity slow down the ascending plume and the forming of the hydrate cap effectively reduces permeability and finally becomes an impermeable seal, thus limiting the movement of CO₂ toward the seafloor. We identify different flow patterns at varied time scales by analyzing the mass distribution of CO₂ in different phases over time. We observe the formation of a fluid inclusion, which mainly consists of liquid CO₂ and is encapsulated by an impermeable hydrate film in the diffusion-dominated stage. The trapped liquid CO₂ and CO₂ hydrate finally dissolve into the pore water through diffusion of the CO₂ component, resulting in permanent storage. We perform sensitivity analyses on storage efficiency under variable geological and operational conditions. We find that under a deep-sea setting, CO₂ sequestration in intact marine sediments is generally safe and permanent.

中文翻译：

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深海沉积物中碳固存的长期可行性。

已提出将深海沉积物中的二氧化碳隔离以长期储存人为CO ₂，从而可以利用当前的海上基础设施。在高压和低温条件下，它具有负浮力作用和水合物形成的优点。然而，对CO ₂注入和注入后命运的多物理场过程以及在不同地质和操作条件下对CO ₂进行海底处置的可行性尚未得到很好的研究。通过对耦合过程的详细研究，我们研究了是否储存CO ₂从长远来看，进入深海沉积物是可行，有效和安全的。我们还研究了多相和多组分流动的演变以及水合物形成对储存效率的影响。结果表明，低浮力和高粘度减缓了上升羽流，水合物顶盖的形成有效地降低了渗透性，最终成为不可渗透的密封，从而限制了CO ₂向海底的运动。通过分析随时间变化的不同阶段中CO ₂的质量分布，我们可以确定在不同时间尺度上的不同流动模式。我们观察到流体夹杂物的形成，其主要由液态CO _2组成并在扩散主导阶段被不可渗透的水合物薄膜包裹。被捕集的液态CO ₂和CO ₂水合物最终通过CO ₂组分的扩散而溶解在孔隙水中，导致永久存储。我们在可变的地质和运营条件下对存储效率进行敏感性分析。我们发现，在深海环境中，完整海洋沉积物中的CO ₂固存通常是安全和永久的。