A comparative seismic study of gas chimney structures from active and dormant seepage sites offshore mid-Norway and west-Svalbard

Abstract

Understanding the fluid flow and the related fluid expulsion from gas chimneys and pipe structures is very important to our environment, since seeping methane has a great influence on our Earth’s climate. Chimneys are found in many places in the world, for instance at the Vestnesa ridge offshore western Svalbard and at the Nyegga region on the mid Norwegian margin. Plumbing systems and chimney structures are different in their characteristics and in their sediments. Since early times activity and dormant periods in these regions were responsible for driving fluids out to the seabed and to the water column. Key structures that act as a gateway for gas and gaseous fluids are called pockmarks which are highly abundant in these areas. Faults, fractures, sedimentation rate, permeability, compaction, overpressure generation, gas hydrates, free gas and source are features that are relevant to the plumbing system and the functioning mode of a chimney. Comparing these two areas is important in order to understand how they differ from each other and to determine their driving force. In the future this might help to predict the occurrence of a new seepage of methane or hazards such as submarine slides. High tectonic activity and heat define the Vestnesa ridge and make it different from Nyegga which shows less of such activities. Sub-seabed features in Vestnesa include more chaotic and wider chimney structures compared to Nyegga. Faults are known as good pathways for fluids helping them migrate vertically and laterally. Truncations of the flanks of continuous layers where chimney and pipe structures pierce through could mark the timing of an active period in all three areas. In this study, chimney models and essential characteristics of chimneys were investigated, and a comparison of seeping systems was conducted.