scholarly journals Methane emission and consumption at a North Sea gas seep (Tommeliten area)

2005 ◽  
Vol 2 (4) ◽  
pp. 1197-1241 ◽  
Author(s):  
H. Niemann ◽  
M. Elvert ◽  
M. Hovland ◽  
B. Orcutt ◽  
A. Judd ◽  
...  
Keyword(s):  
North Sea ◽  
Oil And Gas ◽  
Salt Diapir ◽  
Anaerobic Oxidation Of Methane ◽  
Cold Seeps ◽  
The North ◽  
Oxidation Of Methane ◽  
Phylogenetic Cluster ◽  
Carbonate Formation ◽  
Gas Seepage

Abstract. The North Sea hosts large coal, oil and gas reservoirs of commercial value. Natural leakage pathways of subsurface gas to the hydrosphere have been recognized during geological surveys (Hovland and Judd, 1988). The Tommeliten seepage area is part of the Greater Ekofisk area, which is situated above the Tommeliten Delta salt diapir in the central North Sea. In this study, we report of an active seep site (56°29.90'N, 2°59.80'E) located in the Tommeliten area, Norwegian Block 1/9, at 75 m water depth. Here, cracks in a buried marl horizon allow methane to migrate into overlying clay-silt and sandy sediments. Hydroacoustic sediment echosounding showed several venting spots coinciding with the apex of marl domes where methane is released into the water column and potentially to the atmosphere during deep mixing situations. In the vicinity of the gas seeps, sea floor observations showed small mats of giant sulphide-oxidizing bacteria above patches of black sediments and carbonate crusts, which are exposed 10 to 50 cm above seafloor forming small reefs. These Methane-Derived Authigenic Carbonates (MDACs) contain 13C-depleted, archaeal lipids indicating previous gas seepage and AOM activity. High amounts of sn2-hydroxyarchaeol relative to archaeol and low abundances of biphytanes in the crusts give evidence that ANaerobic MEthane-oxidising archaea (ANME) of the phylogenetic cluster ANME-2 were the potential mediators of Anaerobic Oxidation of Methane (AOM) at the time of carbonate formation. Small pieces of MDACs were also found subsurface at about 1.7 m sediment depth, associated with the Sulphate-Methane Transition Zone (SMTZ). The SMTZ of Tommeliten is characterized by elevated AOM and Sulphate Reduction (SR) rates, increased concentrations of 13C-depleted tetraether derived biphytanes, and specific bacterial Fatty Acids (FA). Further biomarker and 16S rDNA based analyses give evidence that AOM at the Tommeliten SMTZ is mediated by archaea belonging to the ANME-1b group and Sulphate Reducing Bacteria (SRB) most likely belonging to the Seep-SRB1 cluster. The zone of active methane consumption was restricted to a distinct horizon of about 20 cm. Concentrations of 13C-depleted lipid biomarkers (e.g. 500 ng g-dw-1 biphythanes, 140 ng g-dw-1 fatty acid ai-C15:0), cell numbers (1.5x108 cells cm-3), AOM and SR rates (3 nmol cm-3 d-1 in the SMTZ are 2-3 orders of magnitude lower compared to AOM zones of highly active cold seeps such as Hydrate Ridge or the Gulf of Mexico.

scholarly journals Methane emission and consumption at a North Sea gas seep (Tommeliten area)

2005 ◽  
Vol 2 (4) ◽  
pp. 335-351 ◽  
Author(s):  
H. Niemann ◽  
M. Elvert ◽  
M. Hovland ◽  
B. Orcutt ◽  
A. Judd ◽  
...  
Keyword(s):  
North Sea ◽  
Salt Diapir ◽  
Anaerobic Oxidation Of Methane ◽  
Cold Seeps ◽  
Oxidation Of Methane ◽  
Phylogenetic Cluster ◽  
Highly Active ◽  
Carbonate Formation ◽  
Gas Seepage ◽  
Archaeal Lipids

Abstract. The Tommeliten seepage area is part of the Greater Ekofisk area, which is situated above the Tommeliten Delta salt diapir in the central North Sea (56°29.90' N, 2°59.80' E, Norwegian Block 1/9, 75 m water depth). Here, cracks in a buried marl horizon allow methane to migrate into overlying clay-silt and sandy sediments. Hydroacoustic sediment echosounding showed several venting spots coinciding with the apex of marl domes where methane is released into the water column and potentially to the atmosphere. In the vicinity of the gas seeps, sea floor observations showed small mats of giant sulphide-oxidizing bacteria above patches of black sediments as well as carbonate crusts, which are exposed 10 to 50 cm above seafloor forming small reefs. These Methane-Derived Authigenic Carbonates (MDACs) contain 13C-depleted, archaeal lipids indicating previous gas seepage and AOM activity. High amounts of sn2-hydroxyarchaeol relative to archaeol and low abundances of biphytanes in the crusts give evidence that ANaerobic MEthane-oxidising archaea (ANME) of the phylogenetic cluster ANME-2 were the potential mediators of Anaerobic Oxidation of Methane (AOM) at the time of carbonate formation. Small pieces of MDACs were also found subsurface at about 1.7 m sediment depth, associated with the AOM zone. This zone is characterized by elevated AOM and Sulphate Reduction (SR) rates, increased concentrations of 13C-depleted tetraether derived biphytanes, and specific bacterial Fatty Acids (FA). Further biomarker and 16S rDNA based analyses of this horizon give evidence that AOM is mediated by archaea belonging to the ANME-1b group and Sulphate Reducing Bacteria (SRB) most likely belonging to the Seep-SRB1 cluster. The zone of active methane consumption was restricted to a distinct horizon of about 20 cm. Concentrations of 13C-depleted lipid biomarkers (e.g. 500 ng g-dw−1 biphythanes, 140 ng g-dw−1 fatty acid ai-C15:0), cell numbers (1.5×108 cells cm−3), AOM and SR rates (3 nmol cm−3 d−1) in the Tommeliten AOM zone are 2–3 orders of magnitude lower compared to AOM zones of highly active deep water cold seeps such as Hydrate Ridge or the Gulf of Mexico.

scholarly journals Phosphorus Species in Deep-Sea Carbonate Deposits: Implications for Phosphorus Cycling in Cold Seep Environments

Minerals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 645
Author(s):  
Junlie Zhou ◽  
Mengran Du ◽  
Jiwei Li ◽  
Hengchao Xu ◽  
Kaiwen Ta ◽  
...  
Keyword(s):  
Deep Sea ◽  
Cold Seep ◽  
Anaerobic Oxidation Of Methane ◽  
Cold Seeps ◽  
Organic P ◽  
Anaerobic Oxidation ◽  
Phosphorus Species ◽  
China Sea ◽  
Oxidation Of Methane ◽  
Deep Sediments

Phosphorus (P) is an important nutrient for biological communities in cold seeps. However, our knowledge on the source, species, and cycling of P in cold seep environments is limited. In this study, the concentration, species, and micro to nanometer scale distribution of P in seep carbonates were examined at three deep-sea cold seeps in the South China Sea and East China Sea. The Ca-P accounts for the largest proportion of P—followed by detrital-P, Fe-P, organic-P, and exchangeable-P. The distribution patterns of Ca-P, detrital-P, and organic-P in the seep carbonates differ from one another, as shown by elemental mapping with NanoSIMS and scanning electron microscopy. The covariation of P with Ca and C reveals that Ca-P co-precipitates with Ca-carbonate, which is linked to the process of sulfate-driven anaerobic oxidation of methane. Organic-P is also observed within biofilm-like organic carbon aggregates, revealing the microbial enrichment of P by fluids in the process of anaerobic oxidation of methane. P with a granulated morphology was identified as detrital-P derived from deep sediments. Most importantly, it is evident that Ca-P is positively correlated to the Fe content in all the seep carbonates. This indicates the likelihood that the dissolved P in cold-seep fluids is released primarily from Fe oxides through Fe-driven anaerobic oxidation of methane in deep sediments. These processes associated with different species of P may have significant implications for P geochemical cycling and anaerobic oxidation of methane impelled by Fe and sulfate reduction in cold seep environments.

scholarly journals A prospective observational study of why people are medically evacuated from offshore installations in the North Sea

BMJ Open ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. e037558
Author(s):  
Anne Waje-Andreassen ◽  
Øyvind Østerås ◽  
Guttorm Brattebø
Keyword(s):  
Observational Study ◽  
North Sea ◽  
Prospective Observational Study ◽  
Oil And Gas ◽  
Record System ◽  
The North ◽  
Transport Services ◽  
Offshore Installations ◽  
Severity Scores ◽  
The North Sea

ObjectivesFew studies have described evacuations due to medical emergencies from the offshore installations in the North Sea, though efficient medical service is essential for the industrial activities in this area. The major oil- and gas-producing companies’ search and rescue (SAR) service is responsible for medical evacuations. Using a prospective approach, we describe the characteristics of patients evacuated by SAR.Design and settingA prospective observational study of the offshore primary care provided by SAR in the North Sea.MethodsPatients were identified by linking flight information from air transport services in 2015/2016 and the company’s medical record system. Standardised forms filled out by SAR nurses during the evacuation were also analysed. In-hospital information was obtained retrospectively from Haukeland University Hospital’s information system.ResultsA total of 381 persons (88% men) were evacuated during the study period. Twenty-seven per cent of missions were due to chest pain and 18% due to trauma. The mean age was 46.0 years. Severity scores were higher for cases due to medical conditions compared with trauma, but the scores were relatively low compared with onshore emergency missions. The busiest months were May, July and December. Weekends were the busiest days.ConclusionThree times as many evacuations from offshore installations are performed due to acute illness than trauma, and cardiac problems are the most common. Although most patients are not severely physiologically deranged, the study documents a need for competent SAR services 24 hours a day year-round. Training and certification should be tailored for the SAR service, as the offshore health service structure and geography differs from the structure onshore.

scholarly journals The Formation of Authigenic Carbonates at a Methane Seep Site in the Northern Part of the Laptev Sea

Minerals ◽  
2020 ◽  
Vol 10 (11) ◽  
pp. 948
Author(s):  
Alexey Ruban ◽  
Maxim Rudmin ◽  
Oleg Dudarev ◽  
Alexey Mazurov
Keyword(s):  
Seawater Temperature ◽  
Cold Seep ◽  
Anaerobic Oxidation Of Methane ◽  
Laptev Sea ◽  
Cold Seeps ◽  
Authigenic Carbonates ◽  
Oxidation Of Methane ◽  
Major Oxide ◽  
Mg Content ◽  
The Laptev Sea

Authigenic carbonates from cold seeps are unique archives for studying environmental conditions, including biogeochemical processes associated with methane-rich fluid migration through the sediment column. The aim of this research was to study major oxide, mineralogical, and stable isotopic compositions of cold-seep authigenic carbonates collected in the northern part of the Laptev Sea. These carbonates are represented by Mg-calcite with an Mg content of 2% to 8%. The δ13C values range from −27.5‰ to −28.2‰ Vienna Peedee belemnite (VPDB) and indicate that carbonates formed due to anaerobic oxidation of methane, most likely thermogenic in origin. The authigenic pyrite in Mg-calcite is evidence of sulfate reduction during carbonate precipitation. The δ18O values of carbonates vary from 3.5‰ to 3.8‰ VPDB. The calculated δ18Ofluid values show that pore water temperature for precipitated Mg-calcite was comparable to bottom seawater temperature. The presence of authigenic carbonate in the upper horizons of sediments suggests that the sulfate–methane transition zone is shallowly below the sediment–water interface.

Development of semi-submersible production vessels and its application to Australian waters

2008 ◽  
Vol 48 (1) ◽  
pp. 241
Author(s):  
Hilde Engelsen ◽  
Henrik Hannus
Keyword(s):  
North Sea ◽  
Environmental Conditions ◽  
Oil And Gas ◽  
Gas Production ◽  
Oil And Gas Production ◽  
The North ◽  
Hull Design ◽  
Steel Catenary Risers ◽  
Drilling Rigs ◽  
In The Beginning

Semi-submersible platforms have a long history in the North Sea. In the beginning they were used mainly as mobile offshore drilling units, but in the last two decades the permanently moored semi-submersible production vessels have become widely used both as gas processing units and combination oil and gas production vessels. The design of production semi-submersibles evolved from that of drilling rigs, but there have since been significant improvements to the design of the hull and the topside configuration in relation to operational requirements and construction processes. The design methods have also been successfully adapted to areas with different environmental conditions, in combination with steel catenary risers and polyester mooring systems. On recent designs, simplifications of the hull systems are being implemented, which ease operation and enhance the passive safety. Finally, the semi-submersible production vessel’s application to Australian waters is discussed with focus on topside layout, hull design and mooring system design. Environmental conditions offshore northwest Australia are compared to North Sea and Gulf of Mexico conditions, along with vessel class and regulatory requirements.

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