ALBERT

Description: The sequestration of CO2 in the deep geosphere is one potential method for reducing anthropogenic emissions to the atmosphere without necessarily incurring a significant change in our energy-producing technologies. Containment of CO2 as a liquid and an associated hydrate phase, under cool conditions, offers an alternative underground storage approach compared with conventional supercritical CO2 storage at higher temperatures. We briefly describe conventional approaches to underground storage, review possible approaches for using CO2 hydrate in CO2 storage generally, and comment on the important role CO2 hydrate could play in underground storage. Cool underground storage appears to offer certain advantages in terms of physical, chemical and mineralogical processes, which may usefully enhance trapping of the stored CO2. This approach also appears to be potentially applicable to large areas of sub-seabed sediments offshore Western Europe.

Description: In the public's imagination, hydrates are seen as either a potential new source of energy to be exploited as the world uses up its reserves of oil and gas or as a major environmental hazard. Scientists, however, have expressed great uncertainty as to the global volume of hydrates and have reached little agreement on how they might be exploited. Both of these uncertainties can be reduced by a better understanding of how hydrates are held within sediments. There are conflicting ideas as to whether hydrates are disseminated within selected lithologies or trapped within fractures comparable to mineral lodes. To resolve this, hydrates have to be examined at all scales ranging from using seismics to microscopic studies. Their position within sediments also influences the stability of methane hydrate in responding to pressure and temperature and how the released gas might transfer to the ocean, atmosphere, or to a transport mechanism for recovery. These results also run parallel with the studies of carbon dioxide hydrate, which is being considered as a potential sequestion medium.

Description: The Selin Co basin in the northern Lhasa terrane includes more than 3000 m of upward coarsening Lower Cretaceous strata, and the sedimentary sequence from the flysch to the molasse indicates the evolution of a foreland basin. Petrographic analysis shows that sandstones are rich in volcanic and sedimentary lithics and most of them fall into recycled orogen and magmatic arc.Uranium–lead (U–Pb) ages were determined for 435 detrital zircons from the Lower Cretaceous strata in the Selin Co basin. Relative probability of detrital zircon ages shows the Eshaerbu Formation was rich in zircon grains with the age of 125–140 and 160–180 Ma, and the Duoni Formation was dominated by one main age cluster of 125–150 Ma. Analysis of the potential provenances suggests the Early Cretaceous zircon grains were primarily derived from the Gangdese magmatic arc to the south. The youngest zircon ages in the lowermost exposure of the Eshaerbru Formation are c. 130 Ma, providing a maximum depositional age of sediments in the Selin Co basin.Collectively, our studies, together with previously documented Cretaceous thrusting in the Lhasa terrane, suggest the Lower Cretaceous Selin Co basin was deposited in a retroarc foreland basin. From 145–90 Ma, a retroarc foreland basin was presumed to develop in the Lhasa terrane, migrating from the south to the north. Crustal thickening, likely associated with the evolution of the retroarc foreland basin, was speculated to start in the Early Cretaceous in the Lhasa terrane.

Description: Lateglacial-Holocene fjord sediments in Little Loch Broom preserve evidence of extensive slope instability. The major area of reworking is in the outer loch and mid-loch sill region where ice-contact/ice-proximal deposits of the Lateglacial Assynt Glaciogenic Formation have been disrupted by sliding and mass-flow processes linked to the Little Loch Broom Slide Complex and the adjacent Badcaul Slide. Mass failure was instigated about 14-13 ka BP, and is probably the response of the landscape to deglaciation immediately following the removal of ice support during glacial retreat. An initial phase of translational sliding was followed by rotational sliding, as revealed by the superimposition of scallop-shaped slumps on a larger-scale rectilinear pattern of failure. Paraglacial landscape readjustment may also have been enhanced by episodic seismic activity linked to glacio-isostatic unloading. In the inner fjord, evidence of Holocene mass failure includes the Ardessie debris lobe and a discrete intact slide block preserved within the postglacial basinal deposits. The former is a localized accumulation linked to a fluvial catchment on the adjacent An Teallach massif. These mass-transport deposits may represent an ongoing response to paraglacial processes, albeit much reduced (relative to the major slides) in terms of sediment supply to the fjord.

Description: The Song Hong-Yinggehai (SH-Y) and Qiongdongnan (Qi) basins together form one of the largest Cenozoic sedimentary basins in SE Asia. Here we present new records based on the analysis of seismic data, which we compare to geochemical data derived from cores from Ocean Drilling Program (ODP) Site 1148 in order to derive proxies for continental weathering and thus constrain summer monsoon intensity. The SH-Y Basin started opening during the Late Paleocene-Eocene. Two inversion phases are recognized to have occurred at c. 34 Ma and c. 15 Ma. The Qi Basin developed on the northern, rifted margin of South China Sea, within which a large canyon developed in a NE-SW direction. Geochemical and mineralogical data show that chemical weathering has gradually decreased in SE Asia after c. 25 Ma, whereas physical erosion became stronger, especially after c. 12 Ma. Summer monsoon intensification drove periods of faster erosion after 3-4 Ma and from 10-15 Ma, although the initial pulse of eroded sediment at 29.5-21 Ma was probably triggered by tectonic uplift because this precedes monsoon intensification at c. 22 Ma. Clay mineralogy indicates more physical erosion together with high sedimentation rates after c. 12 Ma suggesting a period of strong summer monsoon in the Mid-Miocene.

Description: One practical method to reduce environmentally damaging greenhouse gas emissions is through the geological storage of carbon dioxide. Deep, warm storage of carbon dioxide is currently taking place at Sleipner, North Sea and Weyburn, Canada. It is, however, also possible to store carbon dioxide as a liquid and hydrate in cool, sub-seabed sediments. Offshore north and west of Scotland seafloor pressures and temperatures are suitable for hydrate formation. In addition to the possibility of natural methane hydrate being present in this region, conditions may also be favourable for carbon dioxide storage as a liquid and hydrate. A computer program has been developed to calculate the depth to the base of the carbon dioxide and methane hydrate stability zones in two offshore regions: the Faeroe-Shetland Channel and the northern Rockall Trough. Results predict that methane hydrate remains stable to a maximum depth of 650 m below the seabed in the Faeroe-Shetland Channel, and 600 m below the seabed in the northern Rockall Trough; the carbon dioxide hydrate stability zone extends below the seabed to a depth of 345 and 280 m, respectively. No physical evidence for the existence of natural hydrate in these regions has been confirmed. Suitable conditions for carbon dioxide storage as a liquid and hydrate exist, and should this storage method be developed further, a more refined program and greater offshore investigations to improve data sets would be necessary to scope the full potential.

Description: The Kish Bank Basin lies in the western Irish Sea c. 20 km east of Dublin. It is one of a number of remnants of a larger Permo-Triassic basin system that may have extended across the whole of the Irish Sea. It has a geological history similar to that of the East Irish Sea Basin, initially developing by the reactivation of Caledonian faults that controlled subsequent deposition during Dinantian and Namurian time, with Westphalian deposition in a sag-basin that overstepped the adjacent basement highs. Variscan dextral transpression resulted in the formation of the Codling and Bray faults, and Permian to Jurassic extension formed a set of north-south-trending faults. Liassic outliers are preserved in the hanging walls of the basin margin faults. Early Cretaceous uplift was followed by chalk deposition. Tertiary movements reactivated older faults, isolating the Kish Bank Basin, and producing 9 km of dextral strike-slip along the Codling Fault Zone. The main reservoir in the hydrocarbon play is provided by the Sherwood Sandstone Group, as successfully exploited in the East Irish Sea. Three wells have been drilled to test this reservoir. These encountered high-quality Sherwood Sandstone reservoirs beneath the good potential seal of the Mercia Mudstone Group (which included thick halites). Source rock potential is from either the Westphalian Coal Measures, as penetrated in well 33/22-1, or from inferred Dinantian to Namurian basinal shales. There is good evidence of an active source system, with oil shows in wells 33/17-1 and 33/22-1, data from geochemical analysis of sea-bed cores, a Seepfinder' survey, sea-bed mounds and seismic evidence of shallow gas. The main risks of the play are the migration pathway and the timing of trap formation with respect to migration. Migration favours the eastern side of the basin, and many of the tilted fault blocks that formed during Permian to Jurassic time have been modified by Early Cretaceous inversion and by Tertiary strike-slip compression. All of the structures that have been drilled to date have been either formed or modified after the time of peak hydrocarbon generation and migration.