The ability to detect and monitor any escape of carbon dioxide (CO₂) from sub-seafloor CO₂ storage reservoirs is essential for public acceptance of carbon capture and storage (CCS) as a climate change mitigation strategy. Here, we use repeated high-resolution seismic reflection surveys acquired using a chirp profiler mounted on an autonomous underwater vehicle (AUV), to image CO₂ gas released into shallow sub-surface sediments above a potential CCS storage site at 120 m water depth in the North Sea. Observations of temporal changes in seismic reflectivity, attenuation, unit thickness and the bulk permeability of sediment were used to develop a four-stage model of the evolution of gas migration in shallow marine sediments: Proto-migration, Immature Migration, Mature Migration, and Pathway Closure. Bubble flow was initially enabled through the propagation of stable fractures but, over time, transitioned to dynamic fractures with an associated step change in permeability. Once the gas injection rate exceeded the rate at which gas could escape the coarser sediments overlying the injection point, gas began to pool along a grain size boundary. This enhanced understanding of the migration of free gas in near-surface sediments will help improve methods of detection and quantification of gas in subsurface marine sediments.

检测和监测任何从海底 CO ₂储存库中逸出的二氧化碳 (CO ₂ )的能力对于公众接受碳捕获和储存 (CCS) 作为气候变化缓解策略至关重要。在这里，我们使用安装在自主水下航行器 (AUV) 上的啁啾声剖面仪获得的重复高分辨率地震反射勘测，对 CO ₂进行成像气体释放到北海 120 m 水深的潜在 CCS 储存地点上方的浅表次表层沉积物中。利用地震反射率、衰减、单位厚度和沉积物总体渗透率的时间变化观测，建立了浅海沉积物中气体运移演化的四阶段模型：原始运移、未成熟运移、成熟运移和路径关闭。气泡流最初是通过稳定裂缝的扩展实现的，但随着时间的推移，随着渗透率的相关阶跃变化，转变为动态裂缝。一旦气体注入速度超过气体从注入点上方的较粗沉积物逸出的速度，气体开始沿颗粒尺寸边界聚集。