Time-lapse imaging of CO2 migration within near-surface sediments during a controlled sub-seabed release experiment

• Published in: International journal of greenhouse gas control 2021-07, Vol.109, p.103363, Article 103363
• Main Authors: Roche, Ben, Bull, Jonathan M., Marin-Moreno, Hector, Leighton, Timothy G., Falcon-Suarez, Ismael H., Tholen, Madeleine, White, Paul R., Provenzano, Giuseppe, Lichtschlag, Anna, Li, Jianghui, Faggetter, Michael
• Format: Article
• Language: English
• Subjects: Carbon capture and storage; CO2 injection; Fracture propagation; Gas migration; Time lapse seismic imaging
• ISSN: 1750-5836; 1878-0148
• DOI: 10.1016/j.ijggc.2021.103363

•Time-lapse pseudo-3D seismic reflection imaging of CO2 migration in marine sediment.•CO2 is mapped via enhanced reflectivity, acoustic shadowing, and time-shifts of seismic horizons.•CO2 migration initially occurs via stable fracture propagation, then via dynamic fracture propagation.•CO2 began pooling when the gas injection rate exceeded the rate at which gas could escape the sediment.•Dynamic fracture propagation increases sediment permeability and removed gas pooling. 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.