Gas domes in soft cohesive sediments

Barry, Mark A.; Boudreau, Bernard P.; Johnson, Bruce D.

doi:10.1130/g32686.1

Cited by 35 publications

(40 citation statements)

References 25 publications

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“…years BP (Sejrup et al, ). Furthermore, we observe a gentle shoaling of the Witch Ground Formation toward the class 1 pockmarks while S4.1 slightly dips down (Figure a), which may indicate sediment doming prior to pockmark formation (Barry et al, ; Koch et al, ). We therefore conclude that class 1 pockmarks formation initiated between 13,165 ± 55 and 26,595 ± 387 cal.…”

Section: Discussionmentioning

confidence: 62%

Pockmarks in the Witch Ground Basin, Central North Sea

Böttner

Berndt

Reinardy

et al. 2019

Geochem Geophys Geosyst

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Marine sediments host large amounts of methane (CH4), which is a potent greenhouse gas. Quantitative estimates for methane release from marine sediments are scarce, and a poorly constrained temporal variability leads to large uncertainties in methane emission scenarios. Here, we use 2‐D and 3‐D seismic reflection, multibeam bathymetric, geochemical, and sedimentological data to (I) map and describe pockmarks in the Witch Ground Basin (central North Sea), (II) characterize associated sedimentological and fluid migration structures, and (III) analyze the related methane release. More than 1,500 pockmarks of two distinct morphological classes spread over an area of 225 km2. The two classes form independently from another and are corresponding to at least two different sources of fluids. Class 1 pockmarks are large in size (>6 m deep, >250 m long, and >75 m wide), show active venting, and are located above vertical fluid conduits that hydraulically connect the seafloor with deep methane sources. Class 2 pockmarks, which comprise 99.5% of all pockmarks, are smaller (0.9–3.1 m deep, 26–140 m long, and 14–57 m wide) and are limited to the soft, fine‐grained sediments of the Witch Ground Formation and possibly sourced by compaction‐related dewatering. Buried pockmarks within the Witch Ground Formation document distinct phases of pockmark formation, likely triggered by external forces related to environmental changes after deglaciation. Thus, greenhouse gas emissions from pockmark fields cannot be based on pockmark numbers and present‐day fluxes but require an analysis of the pockmark forming processes through geological time.

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Section: Discussionmentioning

confidence: 62%

Pockmarks in the Witch Ground Basin, Central North Sea

Böttner

Berndt

Reinardy

et al. 2019

Geochem Geophys Geosyst

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“…Figure 18 illustrates the ratio of the predicted overpressure from Equation (25) and the overpressure measured in the domes created by Barry et al (2012b) as a function of the ratio of the dome radius, a, to the thickness of the overlying sediment, h. There is excellent agreement for thin eccentric domes. Equation (25) is based on the assumption that h << a (i.e., a thin plate) and when that is violated, one would expect some deviations, and that is what is seen in Figure 18 for a/h < 5.…”

Section: Large Accumulationsmentioning

confidence: 69%

“…There are unfortunately no data on the internal pressure within such domes, which is crucial in answering this question. However, Barry et al (2012b) devised an experimental and modeling study to shed some light on the problem. They created small-scale domes in the laboratory from a gas flow below a layer of sediment.…”

Section: Large Accumulationsmentioning

confidence: 99%

The physics of bubbles in surficial, soft, cohesive sediments

Boudreau

2012

Marine and Petroleum Geology

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133

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“…Surface slicks and seafloor fluid flow features represent the location and intensity of present‐day seepage associated with distinct fluid migration processes. Widespread pockmarks within mini‐basins are interpreted as the result of pore‐water and biogenic gas migration derived from early sediment compaction and near‐surface diagenesis of organic rich sediments (Bjørlykke, ; Horsfield & Rullkotter, ; Barry et al ., ). In contrast, pockmarks linked with deeper plumbing systems are often isolated and characterized by systematic distributions in relation to fluid migration paths (Ligtenberg, ; Gay et al ., ; Judd & Hovland, ; Andresen et al ., ).…”

Section: Discussionmentioning

confidence: 97%

Subsurface fluid flow in the deep‐water Kwanza Basin, offshore Angola

et al. 2016

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Integrated analysis of high-quality three-dimensional (3D) seismic, seabed geochemistry, and satellite-based surface slick data from the deep-water Kwanza Basin documents the widespread occurrence of past and present fluid flow associated with dewatering processes and hydrocarbon migration. Seismic scale fluid flow phenomena are defined by seep-related seafloor features including pockmarks, mud or asphalt volcanoes, gas hydrate pingoes, as well as shallow subsurface features such as palaeo-pockmarks, direct hydrocarbon indicators (DHIs), pipes and bottomsimulating reflections (BSRs). BSR-derived shallow geothermal gradients show elevated temperatures attributed to fluid advection along inclined stratigraphic carrier beds around salt structures in addition to elevated shallow thermal anomalies above highly conductive salt bodies. Seabed evidences of migrated thermogenic hydrocarbons and surface slicks are used to differentiate thermogenic hydrocarbon migration from fluid flow processes such as dewatering and biogenic gas migration. The analysis constrains the fluid plumbing system defined by the three-dimensional distribution of stratigraphic carriers and seal bypass systems through time. Detailed integration and iterative interpretation have confirmed the presence of mature source rock and effective migration pathways with significant implications for petroleum prospectivity in the post-salt interval. Integration of seismic, seabed geochemistry and satellite data represents a robust method to document and interpret fluid flow phenomena along continental margins, and highlights the importance of integrated fluid flow studies with regard to petroleum exploration, submarine geohazards, marine ecosystems and climate change.

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Gas domes in soft cohesive sediments

Cited by 35 publications

References 25 publications

Pockmarks in the Witch Ground Basin, Central North Sea

Pockmarks in the Witch Ground Basin, Central North Sea

The physics of bubbles in surficial, soft, cohesive sediments

Subsurface fluid flow in the deep‐water Kwanza Basin, offshore Angola

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