Geological controls on shallow gas distribution and seafloor seepage in an Arctic fjord of Spitsbergen, Norway

Roy, Srikumar; Senger, Kim; Hovland, Martin; Römer, Miriam; Braathen, Alvar

doi:10.1016/j.marpetgeo.2019.05.021

Cited by 23 publications

(22 citation statements)

References 71 publications

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“…Past gas leakage indicated by pockmarks throughout Isfjorden has been relatively common (Roy et al, 2015) and a baseline study was conducted for Adventfjorden (Roy et al, 2014). Recently, thermogenic gas seepage was documented in Isfjorden and Storfjorden (Liira et al, 2019), and active gas seepage through the water column in Nordfjorden (Roy et al, 2019).…”

Section: Bathonian To Albian Outcrops Adventdalen Group Lower Cretaceous Volcanicsmentioning

confidence: 99%

You learn as long as you drill; research synthesis from the Longyearbyen CO2 Laboratory, Svalbard, Norway

Olaussen¹,

Senger²,

Braathen³

et al. 2020

NJG

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From 2007 to 2015, eight wells were drilled and fully cored to test the feasibility of storing CO 2 emitted from the coal-fueled power plant in Longyearbyen, Svalbard. The drilling campaign identified three water-bearing sandstone aquifers; i) a lower aquifer in Upper Triassic strata; ii) a middle aquifer in Upper Triassic to Middle Jurassic; and iii) an upper aquifer in Lower Cretaceous strata. Only the two former are regarded as potential CO 2 storage units. Both units are unconventional reservoirs (storage units) consisting of fractured, low-porosity and low-permeability sandstones. The storage units are capped by a c. 400 m-thick Middle Jurassic to Lower Cretaceous mudstone-dominated succession, which acts as an efficient top seal. In addition, a c. 120 m-thick zone of permafrost provides an additional seal. Apart from characterising the CO 2 storage and cap-rock system, the drilling resulted in several unexpected results. These include: (a) the detection of severe underpressure of approximately 50 bar in the two storage units, (b) the discovery of gravity-flow deposits attributed to a hitherto unknown Hauterivian clastic wedge, and (c) the detection of producible thermogenic shale gas at a depth of 640 to 700 m. Moreover, core and wireline data from the wells combined with correlation to equivalent strata in nearby outcrops provide new insights into the age and depositional evolution of the succession. Thus, the data obtained from this project contributes to the regional stratigraphic understanding of the Mesozoic succession in Svalbard and the northern Barents Shelf. Until now, nearly 70 papers have been published in international peer-reviewed journals using data from or part of the Longyearbyen CO 2 Laboratory. In addition, 13 PhD candidates and 27 master students, linked to the project or using obtained data from the project, have graduated. The main achievement of our studies is that we have shown that unconventional fractured reservoirs are suitable for storing CO 2 .

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Section: Bathonian To Albian Outcrops Adventdalen Group Lower Cretaceous Volcanicsmentioning

confidence: 99%

You learn as long as you drill; research synthesis from the Longyearbyen CO2 Laboratory, Svalbard, Norway

Olaussen¹,

Senger²,

Braathen³

et al. 2020

NJG

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“…The fluids escaping from these pockmarks could either be biogenic-or 488 thermogenic-sourced or of mixed origin. We further suggest that pore-water escape from the shallow 489 glacimarine deposits could have also led to the formation of pockmarks, as suggested in other 490 glacimarine settings Roy et al, 2019), however, pore-water escape would not support 491 the formation of mounds within pockmarks. 492 493 Low-relief seabed mounds are found in Queenie Corner in the eastern part of the WISMB, which is 494 characterised by sandy-mud seafloor sediments (Fig.…”

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confidence: 76%

Geological settings and controls of fluid migration and associated seafloor seepage features in the north Irish Sea

Coughlan

Roy

O’Sullivan

et al. 2021

Marine and Petroleum Geology

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Shallow gas accumulation in unconsolidated Quaternary sediments, and associated seepage at the seafloor, is widespread in the north Irish Sea. This study integrates high-resolution seafloor bathymetry and sub-surface geophysical data to investigate shallow gas accumulations and possible fluid (gas and/or liquids) migration pathways to the seafloor in the northern part of the Irish Sea. Shallow gas occurs broadly in two geological settings: the Codling Fault Zone and the Western Irish Sea Mud Belt. The gas has been recognised to accumulate in both sandy and muddy Quaternary marine near-surface sediments and is characterised by three characteristic sub-bottom acoustic features: i) enhanced reflections, ii) acoustic turbid zones, and iii) acoustic blanking. The seepage of shallow gas at the seafloor has resulted in the formation of morphological features including methane-derived authigenic carbonates, seabed mounds and pockmarks. In many instances, the evidence for this gas as biogenic or thermogenic in origin is inconclusive. Two distinct types of pockmarks are recorded in the Western Irish Mud Belt: pockmarks with a relatively flat centre, and pockmarks with a central mound. Based on our observation and existing models, we infer that the formation of a carbonate crust at the seabed surface, is needed as a precursor for the creation of such mounds within pockmarks. The formation processes are interpreted to be different for sandy versus muddy sediments, due to variability in erodibility and sealing capacities of the substrate. We suggest that the origin of these features is linked to the presence of deeper hydrocarbon source rocks with existing and reactivated faults forming fluid migration pathways to the surface. This in turn could indicate a mixed thermogenic-biogenic origin for seeprelated structures in the study area. These features have significant implications for the future development of offshore infrastructure including marine renewable energy as well as for seabed ecology and conservation efforts in the Irish Sea.

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“…Rising pressures from the accumulating fluids produce an upward force, which causes sediment doming (Roy et al, 2019). On the other hand, not all the chimneys extend to the seafloor, forming seafloor expressions, which may indicate that the venting is gradual and focused (Hillman et al, 2018).…”

Section: Relationships Between Observed Geophysical Anomalies and Met...mentioning

confidence: 99%

Geophysical evidence for submarine methane seepage on the Western slope of Okinawa Trough

Luo

Cai

et al. 2022

Front. Earth Sci.

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Identifying seafloor methane seepage efficiently has important implications for assessing environmental impact, reducing the uncertainty of top seal integrity, understanding the petroleum system, and mitigating the drilling hazards due to shallow gas influx. Pore water geochemistry analyses suggest that the study area has an extremely high methane seepage flux and active methane anaerobic oxidation processes. However, geochemical data cannot provide details about the internal seepages. The geophysical dataset from the Western slope of Okinawa Trough, including 2D high-resolution seismic, sub-bottom profiles, and bathymetry, gives us a good opportunity to understand the detailed characteristics of methane seepages in this study. Geophysical data have revealed numerous methane seepage-related features such as seismic chimneys, pockmarks, submarine domes, and amplitude anomalies, including bright spots and enhanced reflections. Pockmarks and domes are often associated with seismic chimneys, indicating that fluid migration is important in their formation. The various geophysical expressions may represent different stages of methane seepage. Fluid quickly drains, causing severe sediment deformation and forming pockmarks, whereas domes may indicate the early stages of fluid discharge. Chimneys that do not extend to the seafloor may indicate that the venting is gradual and focused. Flares linked to domes or pockmarks may indicate that the fluid migration is active. Several factors triggered the existence of methane seepages on the Western slope of the Okinawa Trough, including tectonic setting, overpressure and rapid sedimentation.

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Geological controls on shallow gas distribution and seafloor seepage in an Arctic fjord of Spitsbergen, Norway

Cited by 23 publications

References 71 publications

You learn as long as you drill; research synthesis from the Longyearbyen CO2 Laboratory, Svalbard, Norway

You learn as long as you drill; research synthesis from the Longyearbyen CO2 Laboratory, Svalbard, Norway

Geological settings and controls of fluid migration and associated seafloor seepage features in the north Irish Sea

Geophysical evidence for submarine methane seepage on the Western slope of Okinawa Trough

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