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Riko Noormet; lowering valuable monitoring equipment over board.
Riko Noormets and his team from UNIS study the distribution of pockmarks and
their likely formation mechanisms linked to potential fluid migration pathways.
The area enclosed by the dashed lines in the north-
west of the fjord has c. 25–30 unit-pockmarks
High-resolution multibeam bathymetric data from SA1 (Adventfjorden); show-
ing the distribution of pockmarks.
Top insert; magnified unit-pockmarks on bathymet-
ric data).
Bottom inset illustrates the acoustic turbidity zone
beneath a pockmark on the sub-bottom profile.
Fluid migration pathways to seafloor seepage
Figure b
y: Srik
umar
, R. et al 2014
Marine baseline study for the Longyearbyen CO2 Lab
-
Roy et al. 2014
The target saline aquifer dips 1–3° 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-in-
jection 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 ba-
thymetric 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 acous-
tic blankings interpreted on subbottom acoustic profiles suggest possible gas accumulation and migration linked to
various fault systems reaching the seafloor. This research discusses fluid migration in a fold-and-thrust belt setting,
broadened by secondary sealing mechanisms in Arctic conditions.
Based on the integrated analysis of the high-resolution geophysical datasets along with the structural mapping of
the fold-thrust belt complex in the aquifer and caprock succession, the work conclude that:
• 398 pockmarks mapped on the multibeam bathymetric data provide evidence of past seepage of natural fluids
to the seafloor.
• The occurrence of unit-pockmark clusters suggests a possible ongoing seepage of fluids. The combined pres-
ence of turbidity zones and enhanced reflectors in the marine sediments beneath the densely pockmarked sea-
floor suggests the presence of suspected gas in the shallow stratigraphy of the two study areas.
• Vertical acoustic blankings (gas chimneys) detected in shallow sediments and low backscatter anomalies
from pockmarks suggest possible gas migration through marine sediments and the presence of trapped gas
within the surface sediments of the pockmarks, respectively.
• The spatial linkage and alignment of pockmarks with the ridges, which are interpreted as seafloor expres-
sions of the fold-and-thrust complex, suggest a focused fluid migration along thrust faults in inner Isfjorden.
• The presence of deep faults in the reservoir and caprock succession possibly plays a vital role in the vertical
ascent of fluids and hence generation of pockmarks in Adventfjorden.
• The evidence of focused fluid seeps on the seafloor, suspected shallow gas occurrences located above shal-
low- and deep-rooted sub-horizontal to vertical faults spreading from the décollement layers and fractured
bedrock affected by the fold-and-thrust belt suggests that fluids possibly follow(ed): sub-horizontal to verti-
cal permeable pathways.
• The mapped thrust faults sub-cropping on the seafloor and seep locations identified on bathymetric and si-
descan sonar data could be potential sites for future monitoring of possible CO2 migration.
Geochemical analyses of the pore fluids are needed for linking the seabed seeps to potential sources and for a
better understanding of their migration processes.