Prediction of the distribution Of CO2 injected in the Sleipner area (North Sea) is a major topic of the international research project SACS. We report here a summary of detailed geological interpretations of the depository (the Mio-Pliocene Utsira Sands), based on seismic, wireline-log and sample data. We expect that CO2 will ultimately migrate to the top of the Utsira Sands which is formed by the base of a Pliocene shale unit, or into an eastward thickening sand wedge closely above the base of the Pliocene shales. Therefore, and since CO2 migration is primarily buoyancy driven, we consider the topography of the tops of these two alternative reservoirs to be of utmost importance for the medium-term migration pattern.The two barrier surfaces were mapped at 3D seismic resolution and were used in various representations (different interpreters, time domain, depth domain etc.) as input for migration simulations employing the secondary migration simulator SEMI. Migration below the top Utsira Sands is predicted to take place in a north-westward direction and will probably be not more than ca. 12 km for a total injected quantity of 20 Mill. metric tons CO2. Migration below the top sand wedge will take place in a north-eastward direction with the consequence that CO2 will leave the studied area when up to 25% of the planned injection volume will have been trapped. Our simulation results highlight the importance of subtle topography differences (0.3degrees difference in regional dip between the two barrier horizons) on the migration pattern. The large migration distances and the necessary high topography resolution for storage sites in (shallow) aquifers demand modelling capacities not yet available with standard simulation tools.

The East Irish Sea Basin is a simple petroleum system with a complex geological history. The petroleum play comprises a Namurian source with a Sherwood Sandstone Group carrier and reservoir sequence, sealed by shales and salts of the Mercia Mudstone Group. The source underwent rapid burial during the Triassic and Jurassic, reaching a maximum burial depth of 5 km by the end-Cretaceous. Uplift by as much as 2 km took place between 60 and 20 Ma across the basin. One-dimensional modelling predicts that oil generation took place over a temperature range of 70–120°C. Primary gas generation began contemporaneously with oil generation but continued to temperatures >180°C. Pseudo-3D ray tracing modelling of the volume and distribution of hydrocarbons in the Sherwood Sandstone Group, matched to known hydrocarbon discoveries in the East Irish Sea Basin, indicates that before 180 Ma, traps were mainly gas filled. Continuous burial to 144 Ma resulted in an oil leg developing in most traps, with significant oil accumulations present in the south of the basin. Thermogenic gas generation in the Keys Basin displaced oil in the northern traps during the period leading to maximum burial at 65 Ma, by which time the basin was characterized by a distinct northern gas province and a southern oil province. Subsequent uplift from 60 Ma caused trapped gas to expand and further displace oil from most of the remaining traps in the southern part of the basin. Hydrocarbon flow rates were greatest between 65–60 Ma during maximum burial. Subsequently, hydrocarbon flow rates decreased dramatically, although gas generation continued until 20 Ma.

Abstract Recent improvements in the techniques for modelling the flow of oil and gas through carrier systems allow us to compute the column heights of migrating oil and gas stringers. The calculations are performed throughout the history of the basin and suggest that secondary migration occurs at low saturation, and very often with velocities in excess of 100 km/Ma. The migrating hydrocarbon stringer columns are modelled to be very thin, i.e. in the centimetre range, over large areas. This paper discusses the lateral and vertical distribution of the above properties in order to elucidate and quantify the extreme focusing that hydrocarbons can experience during secondary migration. A result of these very efficient migration mechanisms is that we can successfully explore for hydrocarbons, even in traps that require lateral migration distances in excess of 1000 km from source to trap.

A Quick Look secondary migration analysis based on the SEMI program (Sylta 1993) is performed on the hydrocarbon potential of the frontier Voring area on the Norwegian continental margin. The method uses simplified subsidence history, constant geothermal gradients, and hydrocarbons are generated by kinetic reactions applied to grids. The Quick Look feature gives, in a matter of hours, an opportunity to make a secondary migration evaluation of an area. The work is based on the assumption that a flatspot (DHI) in the area is caused by a gas/water contact, and this gas trap is used as the calibration point for the simulations. The results of the simulations will be more reliable if more DHIs are taken into account. This work focused on four announced blocks in the Nyk High-Verna Dome area (se figure) and the respective kitchen areas.

A threefold subdivision of the syn-rift infill of extensional half-grabens, relating distinct lithologies and stratigraphic signatures to the temporal rift development was proposed by Prosser (1993). Subsequently Ravnás and co-workers (1994) have argued that a bipartite subdivision is developed more commonly in underfilled and sediment starved rift-basins. The Jack of late syn-rift sandstone cappings is attributed to low sediment supply despite low rates of tectonic subsidence and rotation. These two models can be seen as end-members in a series of syn-rift architectural patterns present in the middle Jurassic-lowermost Cretaceous of the northern North Sea.

Stratigraphic studies in western Norway during the last decade have revealed that the Weichselian glaciation was more complex than previously assumed (Andersen et al. 1981; Mangerud 1981; Mangerud et al. 1981a, b; Andersen et al. 1983; Miller et al. 1983; Landvik & Mangerud 1985; Larsen et al. 1987; Sejrup 1987). The Alesund Interstadial was originally defined by Mangerud et al. (1981a, b) based on radio­ car bon dates of mollusc shells in basal tills in the Sunnmore region. Based on stratigraphic evi­ dence, this interstadial was correlated with the last ice-free period prior to the Late Weichselian glacial maximum (Larsen et al. 1987 ) bracketed between 33 and 28 ka. The shell-bearing till, formally named the Rogne Till, was assumed to overlie sediments of Alesund Interstadial age (Mangerud et al. 1981b ). It has become clear, however, that the Alesund Interstadial, as it was first defined, includes sev­ eral ice-free periods (Mangerud et al. 1981b; Miller et al. 1983). The discovery of interstadial sediments covered by at !east two till beds (Hen­ ningsen & Hovden 1984; Landvik & Mangerud 1985) and the identification of three Weichselian glacial episodes in the Skjonghelleren record (Larsen et al. 1987) reveal that the glacial record in the area includes more than the Rogne Till. Sediment sequences 100 to 150 m thick are found on the islands west of Alesund (Flaten 1980; Hamborg & Lien 1984). To follow up the stratigraphical investigations at Godoya (Landvik 1982; Landvik & Mangerud 1985) and the map­ ping of the Quaternary sediments of Vigra and adjacent areas (Hamborg 1983; Hamborg & Lien 1984; Greve 1984), a program was initiated to study the Weichselian glacial stratigraphy on the island of Vigra. The distance from the coast between Nordfjord and Romsdalsfjorden (Fig. l) to the continental shelf edge is on! y 65 km. A well-developed strand­ flat is found as a bedrock rim around several of the outer islands, and 4 00 to 50 0 m high plateaus dose to the present coast represent remnants of the paleic surface, today dissected by 300 to 600 m deep fjords. Further inland, alpine summits reach 1500 m a.s.l.