Simulating seismic chimney structures as potential vertical migration pathways for CO2 in the Snøhvit area, SW Barents Sea: model challenges and outcomes

Abstract

Carbon capture and storage (CCS) activities at the Snohvit field, Barents Sea, will involve carrying out an analysis to determine which parameters affect the migration process of CO2 from the gas reservoir, to what degree they do so and how sensitive these parameters are to any changes. This analysis will aim to evaluate the effects of applying a broad but realistic range of reservoir, fault and gas chimney properties on potential CO2 leakage at various depths throughout the subsurface. Fluid flow might take place through parts of or the entire extent of the overburden. One of the aims of the analysis is assessing the potential of CO2 reaching the seabed. Using the Snohvit gas reservoir and overburden in the Barents Sea, a series of geological models were built using seismic and well-log data. We then performed numerical simulations of CO2 migration in focused fluid flow structures. Identification of potential migration pathways and their extent, such as gas chimneys and faults, and their incorporation into these models and simulations will provide a realistic insight into the migration potential of CO2. In the simulations the CO2 is injected over a 20 year period at a rate of 0.7 Mt/year and migration is allowed to take place over a 2000 year time frame for domains of approximately 21 km2 for the caprock fault models, 24 km2 for the realistic gas chimney models and 35 km2 for the generic gas chimney models, in a layered sedimentary succession. The total mass of CO2 injected in the reservoir during the 20-year injection period is 14 Mt. There is a strong interaction between the various parameters but the parameter that had the most influence on the CO2 migration process was probably the permeability of the reservoirs, especially the average permeability (k). Also, for the faulted caprock scenarios, it should be noted that at near surface depths the permeability of 765 mD is already adequate for a good CO2 flow. At the chimney top level (600 m) however, a further increase in permeability has an additional effect on improving CO2 flow. Overall, considering the slow upward migration velocity of the plume, this geological setup can be regarded as a suitable storage site.