Dynamic response of gas hydrates to lithological changes: evidence from the Mid-Norwegian continental margin Nicolas Waldmann, Haflidi Haflidason, Christine Zühlsdorff and Berit Oline Hjelstuen Department of Earth Science, University of Bergen, Allègaten 41, N-5007 Bergen, Norway nicolas.waldmann@geo.uib.no SEABED III (Norwegian Deepwater Programme) Geophysical signatures of gas hydrates A second, deeper BSR is also occasionally recog- nized on the Vøring Plateau and has been inter- preted as a fossil base of the GHSZ caused by hydrate dissociation during postglacial sea level rise and increase bottom water temperature (Berndt et al., 2004). Yet, its occurrence is patchy and discontinuous. Gas hydrate bearing sediments are commonly detected in seismic profiles by the presence of cross-cutting bottom simulating reflectors (BSR’s) (profiles below), which commonly corresponds to the base of the GHSZ. Yet, gas hydrates have been retrieved as well in regions where BSR’s were acoustically not identified. The GANS project (Gas hydrates on the Norway-Barents Sea -Svalbard margin) is an initiative leaded by the Department of Earth Science, University of Bergen and in collaboration with five research institutions and the Norwegian Deepwater Program SEABED III. The contract number is 175969/S30. Thermodynamic changes at depth might have triggered gas hydrate to become unstable. This situation probably generated overpressure in the sedimentary column and eventually release of from Hovland and Svendsen, 2006 Storegga wall Nyegga pockmark area Fig. B A 150m 150m B On the Vøring Plateau, BSR’s are recognized cross cutting different seismic facies: whether deep hemipelagic marine deposits (in the Nyegga region, profile above) or shallower strata consist- ing of mixed glacial and redeposited material with decrease permeability (in the Trænadjupet slide area, figure below). The mid-Norwegian continental margin (figure on the right) presents a unique situation where thick glacigenic units were deposited during past glacial intervals covering older, highly faulted, fine- grained hemipelagic siliceous ooze se- quences (figure below). These strati- graphic circumstances, combined with features indicating large amount of biogenic methane and probably deep thermogenic methane reservoirs, provide a natu- ral laboratory where to study the development and dynamics of methane hydrates and other diagenesis processes in relation to different sedimentary facies. x1000 Milliseconds 6 4 2 0 20 40 60 80 100 120 140 160 180 200 220 240 260 28 300 320 340 360 380 400 420 440 460 480 km A’ A NW ESE Vøring Basin Trøndelag Platform Vøring Marginal High Opal A/CT Helland-Hansen Arch Vøring Escarpment ? 1 : 500.000 40°E 0° 60°N 80°N 70°N 20°E 20°W 40°W 1000 km Vøring basin The Mid-Norwegian continental margin A A’ Møre basin Upper Jurassic Triassic Paleozoic Cenomanian Aptian Top Paleocene Upper Pliocene Upper Eocene Sills and dikes GS08-155-47GC Ca/Fe 3 2 1 0 Grain size fractions (%) 125-63µm 150-125 µm 1000-150 µm >1000 µm 13.96 ka 14.51 ka 15.09 ka 14 C (uncorrected) II III IV I 0 20 40 Ti/K 1.0 0.6 0.8 0.1 0.2 0.3 Mag. Susc. (10 -5 SI) 0 40 80 120 Depth (m) The depositional environment in Nyegga since the last deglaciation is typified by different sedi- mentary facies reflecting climatic changes (figure below). The Ca/Fe record mainly indicates biopro- ductivity and IRD supply of detrital carbonates. The Ti/K serves to indicate sediment sources and thus transport processes. While K is related to clay minerals supplied by the ice sheets, Ti originates from alterated basalts of the Faeroe-Shetland ridge and is transported by ocean currents. Bulk geochemical records are applicative for correlating the various sediment cores retrieved from Nyegga. Being particularly suitable for this purpose, proved the Ca, Ti, Fe, K and Si element records. Sedimentary environments of the Vøring Plateau Solid gas hydrates are a potentially huge re- source of natural gas. In marine sediments along continental margins, methane hydrate formation is bound by temperature and pres- sure (figure on the right). The depth of the gas hydrate stability zone (GHSZ) is limited by these factors and by sufficient methane con- centration to precipitate hydrate. Additionally, the richness of gas hydrate sys- tems appear to be closely related to the nature of the host sediment, including grain and pore sizes as well as mineralogy. BSR Free gas zone Gas Hydrate Stability Zone (GHSZ) Gas Hydrate Phase boundary Geotherm Free gas Gas Hydrate Sonic velocity - + Temperature Depth / Hydrostatic pressure Seafloor Gas hydrates on continental margins The Norwegian margin was strongly influenced by the Fennoscandian ice sheet during the Pleistocene resulting in increase contribution of fine sediments with average sand content of 5% (figure on the right). Recent studies show that the favorable host sedimentary environment for gas hydrate development is coarse grained deposits due to greater permeability. Yet, the Vøring Plateau mainly consists of fine grained hemipelagic deposits. Environmental conditions Core location and units 150-1000 µm fraction Inflow of warm Atlantic water Glacial processes & cold water conditions Strongly influence of deglaciation (e.g., IRD & melt water plume sedimentation) IV III II I Units W E 1 m Vast technically recoverable gas hydrates resources exist in conti- nental margins, yet most are currently too expensive to produce. This category includes hydrates developing within marine litholo- gies with different permeabilities (figure on the left) representing an enormous future potential, estimated at 5,6 trillion m 3 . Because of the high pressure and relative low temperatures, gas trapped in hydrate cages is highly concentrated with an energy density of ~42% when compared to liquefied natural gas. If captured, these hydrate formations could be abundant reser- voirs of fuel. But while researchers have had some success recov- ering hydrates from permafrost regions in the Arctic, marine sites remain a challenge. Nodules 1cm Nodules 1cm Fractures 1cm Fractures 1cm Gas hydrates on the Nyegga area (the southern margins of the Vøring Plateau) were retrieved as both nodule concentrations and filling fractures (figures on the right) within muddy hemipelagic deposits. Deep water sandstones Non-sandstone with permeability Shales with limited permeability ~3.000.000 ton 3 Increased breakeven price required Increased technology requirements Surficial & shallow hydrate SE Several submarine slides confine the spatial distribution of present day gas hydrates (seismic profile and location map above). This indicates the possible link between methane dissociation and migration with ocean floor destabilization at different temporal scales. Sand fractions (wt. %) Silt (wt. %) Ca/Fe 0 20 40 0 20 40 60 80 0 0.4 0.8 2-4 6 5 1 Mag. susc. (10 -5 SI) Clay (wt. %) Ti/K 0 50 100 150 ) a k ( e g A Depth (m) core MD99-2289/88 40 30 20 10 60 70 80 90 120 130 140 110 MIS 0 100 200 0 40 80 0 0.8 1.2 0 25 20 15 10 5 30 gas from the seafloor to the ocean leaving behind pockmarks as fingerprints of the process (figures above). Trænadjupet slide Sklinnadjupet slide Storegga slide Norway BSR’s Upper profile Lower profile Vøring Plateau Storegga slide Norway BSR’ Nyegga area BSR Base Pleistocene Base Miocene Base Eocene Trænadjupet slide 10 km 400 m NW BSR Opal A/CT Base Pleistocene Chimneys Double BSR 1000 200 meters W E MD99-2289/88 GS08-155-47GC