Continuous inline mapping of a dissolved methane plume at a blowout site in the Central North Sea UK using a membrane inlet mass spectrometer – Water column stratification impedes immediate methane release into the atmosphere

Abstract. Hydroacoustic data document the occurrence of 5 flare clusters and several single flares from which bubbles rise through the entire water column from an active seep site at 40 m water depth in the central North Sea. We investigated the difference in dissolved methane distributions along a 6 km transect crossing this seep site during a period of seasonal summer stratification (July 2013) and a period of well mixed winter water column (January 2014). Dissolved methane accumulated below the seasonal thermocline in summer with a median concentration of 390 nM, whereas during winter, methane concentrations were much lower (median concentration of 22 nM) and punctually elevated due to bubble transport. High resolution methane analysis by an underwater mass-spectrometer confirmed our summer results and were used to document prevailing stratification over the tidal cycle. Although sufficient methane was available, microbial methane oxidation was limited during both seasons. Measured and averaged rate constants (k') using Michaelis Menten kinetics were on the order of 0.01 days-1, equivalent to a turnover time of 100 days. Time series measurements indicated an uptake of only 5–6% of the gas after 4 days, and no known methanotrophs and pmoA-genes were detected. Estimated methane fluxes indicate that horizontal eddy transport rapidly disperses dissolved methane, vertical transport becomes dominant during phases of high wind speeds, and relative to these processes, microbial methane oxidation appears to be comparably low. To bridge the discrete field data we developed a 1-D seasonal model using available year-long records of wind speed, surface temperature and thermocline depth. The model simulations show a peak release of methane at the beginning of fall when the water column becomes mixed. Consistent with our field data, inclusion of microbial methane oxidation does not change the model results significantly, thus microbial oxidation appears to be not sufficient to notably reduce methane during summer stratification before the peak release in fall.

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Methane emissions from abandoned offshore wells– First data from a 2019 research cruise to the Dogger Bank, German North Sea

10.5194/egusphere-egu2020-6792 ◽

2020 ◽

Author(s):

Martin Blumenberg ◽

Stefan Schlömer ◽

Miriam Römer ◽

Katja Heeschen ◽

Hendrik Müller ◽

...

Keyword(s):

Water Column ◽

North Sea ◽

Water Depth ◽

Deep Water ◽

Carbon Dioxide Emissions ◽

Oil And Gas ◽

Methane Emissions ◽

Shallow Gas ◽

Dogger Bank ◽

Central North Sea

Methane is the second most important greenhouse gas and, considering a period of 100 years, has a more than 30 times higher &#8220;global warming potential&#8221; than carbon dioxide. Emissions from the production, storage, distribution and use of fossil energy resources in recent years sum up to about 15 % of global methane emissions with numbers still being under discussion and topic of numerous research programs.Abandoned oil and gas wells are one of the sources of methane from the oil and gas sector. Recent studies found escaping methane at selected abandoned drill holes in the central North Sea. Assuming this would hold for one third of the ~11.000 wells in the region, the process would introduce significant amounts of methane at shallow water depth. Interestingly, the collected methane was of biogenic rather than thermogenic origin, potentially escaping from shallow gas pockets. Likely, this methane was mobilized by mechanical disturbance of the sediments through the drilling operation and the well section has served as a pathway thereafter. However, little is known about the number of wells affected and the relevance for the amounts of methane realeased.During a research cruise with the German research vessel Heincke in July, 2019, we studied seafloor characteristics, water column anomalies and sediment methane geochemistry and further inspected visually nine abandoned well sites at ~40 m water depth in the German sector of the central North Sea (Dogger Bank). The cruise targeted different situations, including known seeps in the Dutch part of the Dogger Bank, well sites of different ages and an area where abandoned wells penetrate shallow gas pockets. First data demonstrate that at none of the studied sites concentrations of dissolved methane were enriched in the upper water column. For most sites, sediment and deep water methane data demonstrate concentrations in the range known as background for that area (i.e., deep water methane close to ~ 10 nM). At one site with high indications for the presence of shallow gas pockets, we observed methane abundances several times enriched compared to background. However, the enrichments also occurred 500 m away from the drill site and did not increase towards the center. Based on our data we argue for an active natural seep situation rather than a leaking well and underline that natural seeps may challenge the identification of potentially leaking wells.

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Seasonal methane accumulation and release from a gas emission site in the central North Sea

Biogeosciences ◽

10.5194/bg-12-5261-2015 ◽

2015 ◽

Vol 12 (18) ◽

pp. 5261-5276 ◽

Cited By ~ 21

Author(s):

S. Mau ◽

T. Gentz ◽

J.-H. Körber ◽

M. E. Torres ◽

M. Römer ◽

...

Keyword(s):

North Sea ◽

Traditional Approach ◽

Turnover Time ◽

Minor Importance ◽

Microbial Oxidation ◽

Dissolved Methane ◽

Oxidation Rates ◽

Median Concentration ◽

Central North Sea ◽

Methane Concentrations

Abstract. We investigated dissolved methane distributions along a 6 km transect crossing active seep sites at 40 m water depth in the central North Sea. These investigations were done under conditions of thermal stratification in summer (July 2013) and homogenous water column in winter (January 2014). Dissolved methane accumulated below the seasonal thermocline in summer with a median concentration of 390 nM, whereas during winter, methane concentrations were typically much lower (median concentration of 22 nM). High-resolution methane analysis using an underwater mass-spectrometer confirmed our summer results and was used to document prevailing stratification over the tidal cycle. We contrast estimates of methane oxidation rates (from 0.1 to 4.0 nM day−1) using the traditional approach scaled to methane concentrations with microbial turnover time values and suggest that the scaling to concentration may obscure the ecosystem microbial activity when comparing systems with different methane concentrations. Our measured and averaged rate constants (k') were on the order of 0.01 day−1, equivalent to a turnover time of 100 days, even when summer stratification led to enhanced methane concentrations in the bottom water. Consistent with these observations, we could not detect known methanotrophs and pmoA genes in water samples collected during both seasons. Estimated methane fluxes indicate that horizontal transport is the dominant process dispersing the methane plume. During periods of high wind speed (winter), more methane is lost to the atmosphere than oxidized in the water. Microbial oxidation seems of minor importance throughout the year.

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THE INFLUENCE OF WATER COLUMN STRATIFICATION ON DISSOLVED OXYGEN LEVELS IN COASTAL AND SHELF WATERS AROUND IRELAND

Biology & Environment Proceedings of the Royal Irish Academy ◽

10.3318/bioe.2010.110.3.195 ◽

2011 ◽

Vol 110 (3) ◽

pp. 195-209 ◽

Cited By ~ 3

Author(s):

Shane O’Boyle ◽

Glenn Nolan

Keyword(s):

Dissolved Oxygen ◽

Water Column ◽

Oxygen Levels ◽

Water Column Stratification ◽

Influence Of Water

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A new parameter set for anisotropic multiparameter full-waveform inversion and application to a North Sea data set

Geophysics ◽

10.1190/geo2015-0349.1 ◽

2016 ◽

Vol 81 (4) ◽

pp. U25-U38 ◽

Cited By ~ 32

Author(s):

Nuno V. da Silva ◽

Andrew Ratcliffe ◽

Vetle Vinje ◽

Graham Conroy

Keyword(s):

North Sea ◽

Waveform Inversion ◽

Real Data ◽

Model Parameters ◽

Full Waveform Inversion ◽

Radiation Patterns ◽

Data Set ◽

Full Waveform ◽

Seismic Image ◽

Central North Sea

Parameterization lies at the center of anisotropic full-waveform inversion (FWI) with multiparameter updates. This is because FWI aims to update the long and short wavelengths of the perturbations. Thus, it is important that the parameterization accommodates this. Recently, there has been an intensive effort to determine the optimal parameterization, centering the fundamental discussion mainly on the analysis of radiation patterns for each one of these parameterizations, and aiming to determine which is best suited for multiparameter inversion. We have developed a new parameterization in the scope of FWI, based on the concept of kinematically equivalent media, as originally proposed in other areas of seismic data analysis. Our analysis is also based on radiation patterns, as well as the relation between the perturbation of this set of parameters and perturbation in traveltime. The radiation pattern reveals that this parameterization combines some of the characteristics of parameterizations with one velocity and two Thomsen’s parameters and parameterizations using two velocities and one Thomsen’s parameter. The study of perturbation of traveltime with perturbation of model parameters shows that the new parameterization is less ambiguous when relating these quantities in comparison with other more commonly used parameterizations. We have concluded that our new parameterization is well-suited for inverting diving waves, which are of paramount importance to carry out practical FWI successfully. We have demonstrated that the new parameterization produces good inversion results with synthetic and real data examples. In the latter case of the real data example from the Central North Sea, the inverted models show good agreement with the geologic structures, leading to an improvement of the seismic image and flatness of the common image gathers.

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Triassic-age salt tectonics of the Central North Sea

Interpretation ◽

10.1190/int-2014-0032.1 ◽

2014 ◽

Vol 2 (4) ◽

pp. SM19-SM28 ◽

Cited By ~ 19

Author(s):

John F. Karlo ◽

Frans S. P. van Buchem ◽

Jan Moen ◽

Katie Milroy

Keyword(s):

North Sea ◽

Lateral Displacement ◽

Salt Tectonics ◽

Structural Relief ◽

Tectonic Style ◽

Thermal Doming ◽

Central North Sea ◽

Extensional Structures

The framework of salt tectonics in the Central North Sea was set early in the Triassic. We defined and illustrated five major domains of differing salt tectonic style. The differing structural styles were all interpreted as having evolved under a component of lateral displacement pairing extensional and contractional structures, produced by some combination of decoupled rift extension and gravity sliding. However, the extensional structures are located toward the basin center and the contractional structures near the original updip limits of salt. This suggests a framework driven by gravity sliding of the sediments overlying the Zechstein away from the Central Graben. Possible mechanisms for structural relief away from the Central Graben are the Triassic focus of rifting lying further east at the Norwegian-Danish basin, footwall uplift of a Triassic Central Graben precursor and significant thermal doming occurring much earlier than had previously been thought. The mechanisms are not mutually exclusive and may have acted in concert.

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Disseminated ‘jigsaw piece’ dolomite in Upper Jurassic shelf sandstones, Central North Sea: an example of cement growth during bioturbation?

Sedimentology ◽

10.1046/j.1365-3091.2000.00319.x ◽

2000 ◽

Vol 47 (3) ◽

pp. 631-644 ◽

Cited By ~ 19

Author(s):

James P. Hendry ◽

Mark Wilkinson ◽

Anthony E. Fallick ◽

Nigel H. Trewin

Keyword(s):

North Sea ◽

Upper Jurassic ◽

Central North Sea

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Q estimation from vertical seismic profile data and anomalous variations in the central North Sea

Geophysics ◽

10.1190/1.1441937 ◽

1985 ◽

Vol 50 (4) ◽

pp. 615-626 ◽

Cited By ~ 54

Author(s):

S. D. Stainsby ◽

M. H. Worthington

Keyword(s):

North Sea ◽

Pulse Width ◽

Spectral Ratio ◽

Seismic Profile ◽

Seismic Attenuation ◽

Recording Equipment ◽

Vertical Seismic Profile ◽

High Attenuation ◽

Vsp Data ◽

Central North Sea

Four different methods of estimating Q from vertical seismic profile (VSP) data based on measurements of spectral ratios, pulse amplitude, pulse width, and zeroth lag autocorrelation of the attenuated impulse are described. The last procedure is referred to as the pulse‐power method. Practical problems concerning nonlinearity in the estimating procedures, uncertainties in the gain setting of the recording equipment, and the influence of structure are considered in detail. VSP data recorded in a well in the central North Sea were processed to obtain estimates of seismic attenuation. These data revealed a zone of high attenuation from approximately 4 900 ft to [Formula: see text] ft with a value of [Formula: see text] Results of the spectral‐ratio analysis show that the data conform to a linear constant Q model. In addition, since the pulse‐width measurement is dependent upon the dispersive model adopted, it is shown that a nondispersive model cannot possibly provide a match to the real data. No unambiguous evidence is presented that explains the cause of this low Q zone. However, it is tentatively concluded that the seismic attenuation may be associated with the degree of compaction of the sediments and the presence of deabsorbed gases.

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