Dedicated : 'Fluids and Fluid Flow' The southwestern Barents Sea is a large hydrocarbon-p... more Dedicated : 'Fluids and Fluid Flow' The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A significant portion of hydrocarbon gases has leaked/migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The leakage of these fluids through marine sediments, due to glacio-tectonics and denudation, may have controlled the evolution of various sedimentary basins of this region. We analyzed 2D seismic data from the southwestern Barents Sea to identify different fluid flow features and study their relationship with the geological setting. Gas chimneys were the most abundant feature observed. Among the various observed fluid flow features were giant gas chimneys covering large areas, associated shallow gas accumulations and fluid leakage along faults. Fluid flow features were located above deep-seated faults in the area suggesting a relation with tectonic processes and glacial cycles.The amount of net erosion in the area showed no direct relation to the distribution of fluid flow features. This suggests fluid flow in the region is caused mainly by repeated glacial cycles and differential geographic uplift, which caused tilting and spilling of various structural traps in the area, although erosion might have had an added effect.
The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A... more The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A significant portion of hydrocarbon gases has leaked/migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The leakage of these fluids through marine sediments,due to glacio-tectonics and denudation, may have controlled the evolution of various sedimentary basins of this region. We analyzed 2D seismic data from the southwestern Barents Sea to identify different fluid-flow features and study their relationship with the geological setting. Gas chimneys were the most abundant feature observed. Among the various observed fluid-flow features were giant gas chimneys covering large areas,associated shallow gas accumulations and fluid leakage along faults. Fluid-flow features were located above deep-seated faults in the area suggesting a relation with tectonic processes and glacial cycles.The proximity of large gas chimneys with major petroleum discoveries suggest a close link between the fluid flow and petroleum systems. The amount of net erosion in the area showed no direct relation to the distribution of fluid-flow features. The strong correlation between major faults and fluid-flow features suggests that extensional tectonics, glaciations and uplift could have played major roles in the timing and activity of fluid leakage.
The Vestnesa Ridge, a gas and gas-hydrate-charged sediment drift on oceanic crust in eastern Fram... more The Vestnesa Ridge, a gas and gas-hydrate-charged sediment drift on oceanic crust in eastern Fram Strait, is the result of the tectonic rifting processes at the North American-Eurasian plate boundary and the initial water mass exchanges between the Nordic Seas and the Arctic Ocean. A revised chronostratigraphic framework with age control based on correlation to ODP Leg 151 holes, constrain the onset of the drift to at least 11 Ma. The drift deposits consist of fine-grained sediments and large quantities of methane stored as marine gas hydrates. The predominant source for the methane is, however, still debated. Potential gas sources may be a mix of biogenic, abiogenic, and thermogenic gas. For the latter, organic-rich Miocene deposits underlying the drift deposits, and leakage of gaseous hydrocarbons from deep-seated reservoirs are debated. The main objective of this study is to carry out a quantitative study on the controlling mechanisms of hydrocarbon migration from potential kitchen areas in the Fram Strait to the leakage points on the Vestnesa Ridge. The study includes the set-up and application of migration modeling techniques by applying the software package Migri to understand potential sources of hydrocarbons, timing of expulsion, and migration pathways towards the seabed. As a baseline for the study, depth converted seismic lines, fault interpretations, borehole data, and other available data are compiled along a 2D line from the central Fram Strait towards the Vestnesa Ridge at a lateral cell resolution of 100 m. Further input to this basin model comprises a siliciclastic lithology set-up at a high vertical resolution that is based on the log-data from ODP Hole 909C. The included Miocene source rock model accounts for lateral and vertical variations of the organic matter quality derived from ODP Hole 909. The results of this modelling study will be a set of gas migration and leakage scenarios that explain the present day gas leakage on the Vestnesa Ridge for either or likely combinations of the three potential gas sources debated and include the Cenozoic basin's history. Besides a best case basin model scenario, most likely (upper 10%) and least likely (lower 10%) estimates on model solution spectrum are derived. These estimates provide information on the sensitivity of the best case solution as they give insight on the range and span of feasible input parameters permitted to explain the present day gas leakage patterns in the study area.
<p>Cold seeps are commonly associated with water column and seabed features. Active... more <p>Cold seeps are commonly associated with water column and seabed features. Active seeps form acoustic flares in the water column and can be detected using data from single or multibeam beam echosounders. They may be associated with pockmarks, but the majority of pockmarks on the Norwegian continental shelf have proven to be inactive. Cold seeps are commonly associated with carbonate crust fields exposed at the seabed. <br>Studies using multibeam echosounder water column data in the Håkjerringdjupet region, underlain by the petroleum province Harstad Basin, have revealed more than 200 active gas flares related to cold seeps. We have studied the seabed around some of these, using the HUGIN HUS AUV equipped with HiSAS 1030 Synthetic Aperture Sonar (SAS) from Kongsberg. The SAS gave a 2 x 150 m wide swath. The primary product is the sonar imagery with a pixel resolution up to c. 3 x 3 cm. For selected areas, bathymetric grids with 20x20 cm grids were produced, giving unrivalled resolution at these water depths. The carbonate crust fields have normally a characteristic appearance, with a low reflectivity and a rugged morphology compared to the surrounding sediments. <br>The interpretation of the acoustic data was verified by visual inspection using the TFish photo system on the AUV, and at a later stage by ROV video footage and physical sampling. The integration of hullborne echosounder data with AUV-mounted acoustic and visual tools provides a very powerful approach for studies of cold seep habitats and related seabed features.<br>An important conclusion from the study is that many pockmarks are not associated with active gas seeps today, and that many of the presently active gas seeps are associated with carbonate crust fields which are readily identifiable from synthetic aperture sonar data.</p>
We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of ... more We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of Vesteralen, northern Norway, to assess (1) hydrocarbon sources, (2) migration pathways and (3) the influence of hydrocarbon seepage on sediment pore water and water column chemistry. The seepage area is characterised by the presence of gas flares in the water column as revealed by hydro acoustic surveys and elevated methane concentrations of up to 42 nM ca. 5 m above the seafloor. Pore water analyses of three gravity cores from the seepage area show varying depths of the sulphate-methane-transition zone (SMTZ) between 80 cm and > 250 cm indicating spatially heterogeneous methane ascent. The isotopic composition of methane (d13C from - 40per mil to - 63per mil and d2H from - 191per mil to - 225per mil) and d13C depth profiles of methane and dissolved inorganic carbon show that the hydrocarbons are predominantly of thermogenic origin, consistent with d13C values of C2 to C4 hydrocarbons...
Dedicated : 'Fluids and Fluid Flow' The southwestern Barents Sea is a large hydrocarbon-p... more Dedicated : 'Fluids and Fluid Flow' The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A significant portion of hydrocarbon gases has leaked/migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The leakage of these fluids through marine sediments, due to glacio-tectonics and denudation, may have controlled the evolution of various sedimentary basins of this region. We analyzed 2D seismic data from the southwestern Barents Sea to identify different fluid flow features and study their relationship with the geological setting. Gas chimneys were the most abundant feature observed. Among the various observed fluid flow features were giant gas chimneys covering large areas, associated shallow gas accumulations and fluid leakage along faults. Fluid flow features were located above deep-seated faults in the area suggesting a relation with tectonic processes and glacial cycles.The amount of net erosion in the area showed no direct relation to the distribution of fluid flow features. This suggests fluid flow in the region is caused mainly by repeated glacial cycles and differential geographic uplift, which caused tilting and spilling of various structural traps in the area, although erosion might have had an added effect.
The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A... more The southwestern Barents Sea is a large hydrocarbon-prone basin of the Norwegian Arctic region. A significant portion of hydrocarbon gases has leaked/migrated into the shallow subsurface and is now trapped in gas hydrate and shallow gas reservoirs. The leakage of these fluids through marine sediments,due to glacio-tectonics and denudation, may have controlled the evolution of various sedimentary basins of this region. We analyzed 2D seismic data from the southwestern Barents Sea to identify different fluid-flow features and study their relationship with the geological setting. Gas chimneys were the most abundant feature observed. Among the various observed fluid-flow features were giant gas chimneys covering large areas,associated shallow gas accumulations and fluid leakage along faults. Fluid-flow features were located above deep-seated faults in the area suggesting a relation with tectonic processes and glacial cycles.The proximity of large gas chimneys with major petroleum discoveries suggest a close link between the fluid flow and petroleum systems. The amount of net erosion in the area showed no direct relation to the distribution of fluid-flow features. The strong correlation between major faults and fluid-flow features suggests that extensional tectonics, glaciations and uplift could have played major roles in the timing and activity of fluid leakage.
The Vestnesa Ridge, a gas and gas-hydrate-charged sediment drift on oceanic crust in eastern Fram... more The Vestnesa Ridge, a gas and gas-hydrate-charged sediment drift on oceanic crust in eastern Fram Strait, is the result of the tectonic rifting processes at the North American-Eurasian plate boundary and the initial water mass exchanges between the Nordic Seas and the Arctic Ocean. A revised chronostratigraphic framework with age control based on correlation to ODP Leg 151 holes, constrain the onset of the drift to at least 11 Ma. The drift deposits consist of fine-grained sediments and large quantities of methane stored as marine gas hydrates. The predominant source for the methane is, however, still debated. Potential gas sources may be a mix of biogenic, abiogenic, and thermogenic gas. For the latter, organic-rich Miocene deposits underlying the drift deposits, and leakage of gaseous hydrocarbons from deep-seated reservoirs are debated. The main objective of this study is to carry out a quantitative study on the controlling mechanisms of hydrocarbon migration from potential kitchen areas in the Fram Strait to the leakage points on the Vestnesa Ridge. The study includes the set-up and application of migration modeling techniques by applying the software package Migri to understand potential sources of hydrocarbons, timing of expulsion, and migration pathways towards the seabed. As a baseline for the study, depth converted seismic lines, fault interpretations, borehole data, and other available data are compiled along a 2D line from the central Fram Strait towards the Vestnesa Ridge at a lateral cell resolution of 100 m. Further input to this basin model comprises a siliciclastic lithology set-up at a high vertical resolution that is based on the log-data from ODP Hole 909C. The included Miocene source rock model accounts for lateral and vertical variations of the organic matter quality derived from ODP Hole 909. The results of this modelling study will be a set of gas migration and leakage scenarios that explain the present day gas leakage on the Vestnesa Ridge for either or likely combinations of the three potential gas sources debated and include the Cenozoic basin's history. Besides a best case basin model scenario, most likely (upper 10%) and least likely (lower 10%) estimates on model solution spectrum are derived. These estimates provide information on the sensitivity of the best case solution as they give insight on the range and span of feasible input parameters permitted to explain the present day gas leakage patterns in the study area.
<p>Cold seeps are commonly associated with water column and seabed features. Active... more <p>Cold seeps are commonly associated with water column and seabed features. Active seeps form acoustic flares in the water column and can be detected using data from single or multibeam beam echosounders. They may be associated with pockmarks, but the majority of pockmarks on the Norwegian continental shelf have proven to be inactive. Cold seeps are commonly associated with carbonate crust fields exposed at the seabed. <br>Studies using multibeam echosounder water column data in the Håkjerringdjupet region, underlain by the petroleum province Harstad Basin, have revealed more than 200 active gas flares related to cold seeps. We have studied the seabed around some of these, using the HUGIN HUS AUV equipped with HiSAS 1030 Synthetic Aperture Sonar (SAS) from Kongsberg. The SAS gave a 2 x 150 m wide swath. The primary product is the sonar imagery with a pixel resolution up to c. 3 x 3 cm. For selected areas, bathymetric grids with 20x20 cm grids were produced, giving unrivalled resolution at these water depths. The carbonate crust fields have normally a characteristic appearance, with a low reflectivity and a rugged morphology compared to the surrounding sediments. <br>The interpretation of the acoustic data was verified by visual inspection using the TFish photo system on the AUV, and at a later stage by ROV video footage and physical sampling. The integration of hullborne echosounder data with AUV-mounted acoustic and visual tools provides a very powerful approach for studies of cold seep habitats and related seabed features.<br>An important conclusion from the study is that many pockmarks are not associated with active gas seeps today, and that many of the presently active gas seeps are associated with carbonate crust fields which are readily identifiable from synthetic aperture sonar data.</p>
We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of ... more We investigated active methane seeps in a water depth of 200 m in the Hola area off the coast of Vesteralen, northern Norway, to assess (1) hydrocarbon sources, (2) migration pathways and (3) the influence of hydrocarbon seepage on sediment pore water and water column chemistry. The seepage area is characterised by the presence of gas flares in the water column as revealed by hydro acoustic surveys and elevated methane concentrations of up to 42 nM ca. 5 m above the seafloor. Pore water analyses of three gravity cores from the seepage area show varying depths of the sulphate-methane-transition zone (SMTZ) between 80 cm and > 250 cm indicating spatially heterogeneous methane ascent. The isotopic composition of methane (d13C from - 40per mil to - 63per mil and d2H from - 191per mil to - 225per mil) and d13C depth profiles of methane and dissolved inorganic carbon show that the hydrocarbons are predominantly of thermogenic origin, consistent with d13C values of C2 to C4 hydrocarbons...
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