Passive acoustic quantification of gas fluxes during controlled gas release experiments

Bergès, Benoît; Leighton, Timothy G.; White, P.R.

doi:10.1016/j.ijggc.2015.02.008

Cited by 65 publications

(41 citation statements)

References 57 publications

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“…The interpretation of multiple mechanisms supports also the analysis of ocean tides on the SDE occurrence. Tidal modulation of gas discharge from gas reservoirs is well documented in a variety of environments (e.g., Algar et al, ; Bergès et al, ; Boles et al, ; Torres et al, ) where intensified gas release was observed during periods of low tide. Thus, missing clear effect of tides on the SDEs occurrence at the MASOX site (Figures b and c) indicate that besides gas seepage‐related source mechanism of the SDEs another mechanism that is weakly influenced by tides is involved and perhaps more efficient in generating SDEs.…”

Section: Discussionmentioning

confidence: 99%

Microseismicity Linked to Gas Migration and Leakage on the Western Svalbard Shelf

Franek

Plaza‐Faverola

Mienert

et al. 2017

Geochem Geophys Geosyst

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The continental margin off Prins Karls Forland, western Svalbard, is characterized by widespread natural gas seepage into the water column at and upslope of the gas hydrate stability zone. We deployed an ocean bottom seismometer integrated into the MASOX (Monitoring Arctic Seafloor‐Ocean Exchange) automated seabed observatory at the pinch‐out of this zone at 389 m water depth to investigate passive seismicity over a continuous 297 day period from 13 October 2010. An automated triggering algorithm was applied to detect over 220,000 short duration events (SDEs) defined as having a duration of less than 1 s. The analysis reveals two different types of SDEs, each with a distinctive characteristic seismic signature. We infer that the first type consists of vocal signals generated by moving mammals, likely finback whales. The second type corresponds to signals with a source within a few hundred meters of the seismometer, either due east or west, that vary on short (∼tens of days) and seasonal time scales. Based on evidence of prevalent seafloor seepage and subseafloor gas accumulations, we hypothesize that the second type of SDEs is related to subseafloor fluid migration and gas seepage. Furthermore, we postulate that the observed temporal variations in microseismicity are driven by transient fluid release and due to the dynamics of thermally forced, seasonal gas hydrate decomposition. Our analysis presents a novel technique for monitoring the duration, intensity, and periodicity of fluid migration and seepage at the seabed and can help elucidate the environmental controls on gas hydrate decomposition and release.

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Section: Discussionmentioning

confidence: 99%

Microseismicity Linked to Gas Migration and Leakage on the Western Svalbard Shelf

Franek

Plaza‐Faverola

Mienert

et al. 2017

Geochem Geophys Geosyst

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“…Timescales for emissions vary widely from observational, through daily, to seasonal (Bergès, Leighton, and White 2015, Kretschmer et al 2015, Leifer and Judd 2015. Timescales for emissions vary widely from observational, through daily, to seasonal (Bergès, Leighton, and White 2015, Kretschmer et al 2015, Leifer and Judd 2015.…”

Section: Trap Integrity and Leaksmentioning

confidence: 99%

A New Look at Seafloor Venting: Natural Gas Hydrate Derivatives

Barnard

Sager

Snow

et al. 2016

Day 3 Wed, May 04, 2016

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Natural leaks of multiphase hydrocarbons from the seafloor are widespread. Characterizing the temporal and spatial variability of these emissions provides baselines for comparison to the magnitude of anthropogenic leaks. Determining leakage rates will be important to our understanding the sustainable implementation of subsea infrastructure and the relative contribution of natural sources to global budgets. Multibeam echo soundings from cruise AT21-02 were used to define a region with several~600 to 900 m tall gas plumes in the water column directly above cratered hummocky regions of the sea floor with high backscatter in water depths of~1500 m over the Barbados Accretionary Complex. The relationship of seafloor morphologic features such as faults, craters, and mud volcanoes with vent-gas plumes in the water column is indicative of substantial emissions from this region. Disappearance of the acoustic plumes at~600 m is coincident with the top of CH 4 gas hydrate stability in the water column. In the plumes, natural gas hydrate shells that form at the gas-water interface and armor the gas from dissolution during ascent likely encapsulate bubbles. Ascent-driven pressure change in the bubbles causes shattering of shells forming gas hydrate shards that rise with the ascending plume and add to its acoustic reflection strength. The multiphase fluid consisting of gas, shelled bubbles, shards, and water changes character at the top of gas hydrate stability where the hydrate dissociates and dissolves. Differentiating sources and further characterizing emissions will provide baselines and also contribute to understanding the relative importance of the different emissions sources.

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“…A key issue with CCS is ensuring that sequestered gas remains in the sub-surface, and that any significant leakage is detectable. In the marine environment there has been experimentation to determine the limits for this detection, as well as localization and quantification of CO 2 leakage from controlled subseabed gas release experiments [8,9,10,11,12,13]. With regard to quantifying gas leakage using acoustic techniques, ambient noise is an essential factor that needs to be considered [14].…”

Section: Introductionmentioning

confidence: 99%

A noise impact assessment model for passive acoustic measurements of seabed gas fluxes

White

Bull

et al. 2019

Ocean Engineering

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Accurate determination of seabed gas flux is important for understanding natural processes as well as giving confidence that the size of any leaks from marine infrastructure can be properly assessed. Acoustic methods for flux determination require a relatively quiet underwater environment, and can fail when there is too much noise from other natural or anthropogenic sources. This study applies an acoustic monitoring example of seabed gas leakage in terms of sound level intensity, to statistically assess and minimize the impact from oceanic noise on seabed acoustic experiments which require relative quiet environment. It addresses the question: how far from a source of radiated ambient noise does a recording hydrophone and location of seabed gas need to be so that acoustic methods for remotely determining gas flux are successful. We develop a model to assess impacts of ambient noise under various conditions, incorporating sound/noise sources (seabed gas leaks, sea surface agitation and shipping) and underwater acoustic propagation. The reliability of the model is tested by comparing measured seabed ambient noise in the central North Sea, and the robustness of it is verified by presenting statistical outliers and a receiver operating characteristic (ROC) curve. A range of scenarios are presented for several gas flow rates, which show the threshold of detection when the recording hydrophone is at different distances from the location of seabed gas escape, and competing noise sources (including shipping and surface waves).

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Passive acoustic quantification of gas fluxes during controlled gas release experiments

Abstract: 10The detection and quantification of an underwater gas release is becoming increasingly

Cited by 65 publications

References 57 publications

Microseismicity Linked to Gas Migration and Leakage on the Western Svalbard Shelf

Microseismicity Linked to Gas Migration and Leakage on the Western Svalbard Shelf

A New Look at Seafloor Venting: Natural Gas Hydrate Derivatives

A noise impact assessment model for passive acoustic measurements of seabed gas fluxes

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