Fluid migration pathways to seafloor seepage in inner Isfjorden and Adventfjorden, Svalbard

This study represents a marine baseline study for the Longyearbyen CO2 Lab, in which CO2 may be injected in the Upper Triassic-Middle Jurassic Kapp Toscana Group, which comprises several permeable beds. The target saline aquifer dips 1-3 degrees southwest and thus crops out 14-16 km northeast from the proposed injection site in both offshore and onshore settings. Since the aquifer is exposed at the surface, a carefully documented pre-injection baseline study is required prior to any injection. The seafloor and its subsurface conditions are analysed and interpreted, where the targeted aquifer and organic-rich top-seal shales sub-crop. High-resolution multibeam bathymetric and backscatter imaging, sub-bottom acoustic profiles, sidescan sonar data and multichannel 2D seismic data were used to analyse seepage-related features on the seafloor and their link to subsurface tectonic structures. In total, 398 pockmarks have been identified on the seafloor, suggesting significant past and/or present natural fluid seepage. Beneath the pockmarks, acoustic features such as enhanced reflections, acoustic turbid zones and acoustic blankings interpreted on sub-bottom acoustic profiles suggest possible gas accumulation and migration linked to various fault systems reaching the seafloor. This paper discusses fluid migration in a fold-and-thrust belt setting, broadened by secondary sealing mechanisms in Arctic conditions. We conclude by illustrating the various types of reported fluid seepage, particularly along permeable fault planes and at the rims of igneous intrusions.