| 1. |
- Lorenz, Henning, Dr. 1972-, et al.
(författare)
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COSC-2 – drilling the basal décollement and underlying margin of palaeocontinent Baltica in the Paleozoic Caledonide Orogen of Scandinavia
- 2022
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Ingår i: Scientific Drilling. - Göttingen : Copernicus Publications. - 1816-8957 .- 1816-3459. ; 30, s. 43-57
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Tidskriftsartikel (refereegranskat)abstract
- Abstract.The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project aims to characterise the structure and orogenic processes involved in a major collisional mountain belt by multidisciplinary geoscientific research. Located in western central Sweden, the project has drilled two fully cored deep boreholes into the bedrock of the deeply eroded Early Paleozoic Caledonide Orogen. COSC-1 (2014) drilled a subduction-related allochthon and the associated thrust zone. COSC-2 (2020, this paper) extends this section deeper through the underlying nappes (Lower Allochthon), the main Caledonian décollement, and the upper kilometre of basement rocks. COSC-2 targets include the characterisation of orogen-scale detachments, the impact of orogenesis on the basement below the detachment, and the Early Paleozoic palaeoenvironment on the outer margin of palaeocontinent Baltica. This is complemented by research on heat flow, groundwater flow, and the characterisation of the microbial community in the present hard rock environment of the relict mountain belt. COSC-2 successfully, and within budget, recovered a continuous drill core to 2276 m depth. The retrieved geological section is partially different from the expected geological section with respect to the depth to the main décollement and the expected rock types. Although the intensity of synsedimentary deformation in the rocks in the upper part of the drill core might impede the analysis of the Early Paleozoic palaeoenvironment, the superb quality of the drill core and the borehole will facilitate research on the remaining targets and beyond. Protocols for sampling in the hard rock environment and subsequent sample preservation were established for geomicrobiological research and rock mechanical testing. For the former, a sparse sample series along the entire drill core was taken, while the target of the latter was the décollement. COSC-2 was surveyed by a comprehensive post-drilling downhole logging campaign and a combined borehole/land seismic survey in autumn 2021. This paper provides an overview of the COSC-2 (International Continental Scientific Drilling Project – ICDP 5054_2_A and 5054_2_B boreholes) operations and preliminary results. It will be complemented by a detailed operational report and data publication.
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| 2. |
- Salas Romero, Silvia
(författare)
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Multidisciplinary Near-Surface Investigation of a Quick-Clay Landslide Prone Area in Southwest Sweden
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quick-clay landslides are considered one of the most important geohazards in Sweden, Norway, and Canada. The deposits involved are glacial and postglacial clays and silty clays, which are very sensitive to increased stress that may collapse their structure and cause liquefaction.A multidisciplinary approach was adopted in this study of quick clays in an area of southwest Sweden that is prone to landslides. It was mainly based on geophysical methods, but was complemented and validated with geotechnical, geological, and hydrological data. Downhole geophysics, land and river reflection seismics, radio magnetotellurics, P-wave refraction tomography, magnetics, and multichannel analysis of surface waves comprised the main geophysical methods used in this research. Laboratory measurements of core samples, such as grain size analysis, mineral magnetic properties, fossil content, X-ray fluorescence, cation exchange capacity, X-ray powder diffraction, electrical conductivity, and pH were also taken. Hydrological modelling was used to obtain information on the properties of groundwater within a coarse-grained layer, given the importance of this information in the formation of quick clays.The evaluation of the physico-chemical properties of the coarse-grained layer revealed high values of magnetic susceptibility, probably as a result of fluvial sorting, which tends to accumulate denser minerals such as magnetite. Potential quick clays were visually observed above this layer, and their presence was also confirmed by geotechnical data acquired in previous studies. Marine fossils identified within the coarse-grained layer confirmed the glaciomarine origin of the clays. Geophysical results revealed the presence of large-scale structures, an undulating fractured bedrock and a coarse-grained layer sandwiched between clay deposits, with leached sediments on top and unleached sediments below. This layer, important for the development of quick clays in the area, was 3D modelled in a regional context. Magnetic data also revealed that the coarse-grained layer together with quick clays, have the potential to act as a sliding prone layer. Multichannel analysis of surface waves helped to geotechnically characterize the area. Although the results could not reach the deeper layers, it did yield information about the shallower layers of clay, silt and sand. The VS30 values indicated the presence of soft soils, as well as soft clays/silts with high plasticity index and high water content.This PhD is expected to improve the current knowledge of quick-clay landslides and how they are preconditioned. Climate change will probably affect the study area in the near future, most likely increasing landslide risk, therefore, research should continue and advance to new levels. Application of other geophysical methods such as borehole or geophysical monitoring, and induced polarization, could provide more information about the formation of quick clays and associated landslides.
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| 3. |
- Sopher, Daniel
(författare)
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Characterization of the structure, stratigraphy and CO2 storage potential of the Swedish sector of the Baltic and Hanö Bay basins using seismic reflection methods
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An extensive multi-channel seismic dataset acquired between 1970 and 1990 by Oljeprospektering AB (OPAB) has recently been made available by the Geological Survey of Sweden (SGU). This thesis summarizes four papers, which utilize this largely unpublished dataset to improve our understanding of the geology and CO2 storage capacity of the Baltic and Hanö Bay basins in southern Sweden.A range of new processing workflows were developed, which typically provide an improvement in the final stacked seismic image, when compared to the result obtained with the original processing. A method was developed to convert scanned images of seismic sections into SEGY files, which allows large amounts of the OPAB dataset to be imported and interpreted using modern software. A new method for joint imaging of multiples and primaries was developed, which is shown to provide an improvement in signal to noise for some of the seismic lines within the OPAB dataset. For the first time, five interpreted regional seismic profiles detailing the entire sedimentary sequence within these basins, are presented. Depth structure maps detailing the Outer Hanö Bay area and the deeper parts of the Baltic Basin were also generated. Although the overall structure and stratigraphy of the basins inferred from the reprocessed OPAB dataset are consistent with previous studies, some new observations have been made, which improve the understanding of the tectonic history of these basins and provide insight into how the depositional environments have changed throughout time. The effective CO2 storage potential within structural and stratigraphic traps is assessed for the Cambrian Viklau, När and Faludden sandstone reservoirs. A probabilistic methodology is utilized, which allows a robust assessment of the storage capacity as well as the associated uncertainty. The most favourable storage option in the Swedish sector of the Baltic Basin is assessed to be the Faludden stratigraphic trap, which is estimated to have a mid case (P50) storage capacity of 3390 Mt in the deeper part of the basin, where CO2 can be stored in a supercritical phase.
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| 4. |
- Sopher, Daniel, et al.
(författare)
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Evaluation of the subsurface compressed air energy storage (CAES) potential on Gotland, Sweden
- 2019
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 78:6
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Tidskriftsartikel (refereegranskat)abstract
- Wind energy is an important field of development for the island of Gotland, Sweden, especially since the island has set targets to generate 100% of its energy from renewable sources by 2025. Due to the variability of wind conditions, energy storage will be an important technology to facilitate the continued development of wind energy on Gotland and ensure a stable and secure supply of electricity. In this study, the feasibility of utilizing the Middle Cambrian Faludden sandstone reservoir on Gotland for Compressed Air Energy Storage (CAES) is assessed. Firstly, a characterization of the sandstone beneath Gotland is presented, which includes detailed maps of reservoir thickness and top reservoir structure. Analysis of this information shows that the properties of the Faludden sandstone and associated cap rock appear favorable for the application of CAES. Seven structural closures are identified below the eastern and southern parts of Gotland, which could potentially be utilized for CAES. Scoping estimates of the energy storage capacity and flow rate for these closures within the Faludden sandstone show that industrial scale CAES could be possible on Gotland.
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| 5. |
- Dehghannejad, Mahdieh, et al.
(författare)
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Reflection seismic imaging of the upper crust in the Kristineberg mining area, northern Sweden
- 2010
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Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 71:4, s. 125-136
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Tidskriftsartikel (refereegranskat)abstract
- The Kristineberg mining area is located in the western part of the Palaeoproterozoic Skellefte Ore District, one of the most important mining districts in Europe. As a part of a 3D geologic modeling project, two new reflection seismic profiles were acquired with a total length of about 20 km. One profile (HR), parallel to previous seismic profiles, was acquired using a 10 m receiver and source interval and crosses the steeply dipping structures of the Kristineberg mine. The other profile (Profile 2) runs perpendicular to all existing profiles in the area. Although the structural geology is complex, the processed seismic data reveal a series of steeply dipping to sub-horizontal reflections, some of which reach the surface and allow correlation with surface geology. Our general interpretation of the seismic images is that the Kristineberg mine and associated mineral horizon are located in the northern part of a series of steeply south dipping structures. Overall, main structures plunge to the west at about 30 degrees-40 degrees. Cross-dip analysis and reflection modeling were carried out to obtain the 3D orientation of the main reflections and to provide insight into the possible contribution of out-of-the-plane reflections. This helped, for example, to obtain the 3D geometry of a deep reflection that was previously interpreted as structural basement to volcanic rocks. The new reflection seismic profiles have improved our understanding of shallow geological structures in the area and in conjunction with recently acquired potential field data, magnetotelluric data and geological observations will help to refine previous 3D geologic modeling interpretations that were aimed at larger scale structures.
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| 6. |
- Tryggvason, Ari, et al.
(författare)
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Reflection seismic investigations in the western part of the paleoproterozoic VHMS-bearing Skellefte district, northern Sweden
- 2006
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 101:5, s. 1039-1054
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Tidskriftsartikel (refereegranskat)abstract
- The Skellefte district forms part of the Svecofennian ca. 1.90 to 1.80 Ga, snpracrustal sequence and associated intrusive rocks in the northern part of Sweden. The western part of the Skellefte district, which is the most important metallogenic province in northern Sweden today, hosts major volcanic-hosted massive Sulfide (VHMS) deposits (e.g., the 23 million metric tons (Mt) Kristineberg Cu-Zn-Pb-Ag-Au deposit). In order to obtain a better understanding of the VHMS ore potential at depth, new seismic reflection data were acquired along two parallel and 25-km-long profiles in the Kristineberg area in 2003. The data were collected with the purpose of obtaining high-resolution images of the top 10 kin of the crust and are presented here for the first time. Although the structural setting is very complex, the stacked sections reveal numerous reflections that can be correlated with surface geology. Visible on both profiles is a pronounced north-dipping hand of reflections marking a boundary between relatively transparent crust above and significantly more reflective crust beneath it. We interpret this reflective crust to represent a structural basement to the ore-bearing Skellefte Group, possibly constituting Bothnian basin metasedimentary rocks bordering the Skellefte district to the south. This new interpretation is important for the understanding of the tectonic evolution of the Skellefte district and for defining exploration strategies in the area. The seismic results suggest that the Kristineberg and Ravliden deposits occur on the northern limb of a kilometer-scale local second-order syncline within the hinge zone of a major antiform. Results from a profile located approximately 8 kin to the west of the Kristineberg mine indicate that the Revsund granitoid has a thickness of about 3 to 3.5 km. Ultramafic rocks are also imaged clearly Diffraction patterns and bright-spot reflectivity is interpreted as originating from either mafic to ultramafic intrusions ora mineralization zone at 3- to 5-km depth. These results help to identify new prospective areas and mineral potential, both downplunge from known ores and on the same stratigraphic horizon on the southern limb of the ore-bearing syncline. The seismic reflection profiling has been effective in imaging the major structures around the Kristineberg orebody, demonstrating that this technique can be used for delineating complex structures significant for mineral exploration.
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| 7. |
- Sopher, Daniel, et al.
(författare)
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The structure and stratigraphy of the sedimentary succession in the Swedish sector of the Baltic Basin : new insights from vintage 2D marine seismic data
- 2016
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 676, s. 90-111
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Tidskriftsartikel (refereegranskat)abstract
- We present five interpreted regional seismic profiles, describing the full sedimentary sequence across the Swedish sector of the Baltic Sea. The data for the study are part of an extensive and largely unpublished 2D seismic dataset acquired between 1970 and 1990 by the Swedish Oil Prospecting Company (OPAB). The Baltic Basin is an intracratonic basin located in northern Europe. Most of the Swedish sector of the basin constitutes the NW flank of a broad synclinal depression, the Baltic Basin. In the SW of the Swedish sector lies the Hand Bay Basin, formed by subsidence associated with inversion of the Tornquist Zone during the Late Cretaceous. The geological history presented here is broadly consistent with previously published works. We observe an area between the Hand Bay and the Baltic Basin where the Palaeozoic strata has been affected by transpression and subsequent inversion, associated with the Tornquist Zone during the late Carboniferous-Early Permian and Late Cretaceous, respectively. We propose that the Christianso High was a structural low during the Late Jurassic, which was later inverted in the Late Cretaceous. We suggest that a fan shaped feature in the seismic data, adjacent to the Christianso, Fault within the Hand Bay Basin, represents rapidly deposited, coarse-grained sediments eroded from the inverted Christianso High during the Late Cretaceous. We identify a number of faults within the deeper part of the Baltic Basin, which we also interpret to be transpressional in nature, formed during the Caledonian Orogeny in the Late Silurian-Early Devonian. East of Gotland a number of sedimentary structures consisting of Silurian carbonate reefs and Ordovician carbonate mounds, as well as a large Quaternary glacial feature are observed. Finally, we use the seismic interpretation to infer the structural and stratigraphic history of the Baltic and Hand Bay basins within the Swedish sector.
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| 8. |
- Juhlin, Christopher, et al.
(författare)
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3D baseline seismics at Ketzin, Germany : The CO2SINK project
- 2007
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Ingår i: Geophysics. - Tulsa, United States : Society of Exploration Geophysicists. - 0016-8033 .- 1942-2156. ; 72:5, s. B121-B132
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Tidskriftsartikel (refereegranskat)abstract
- A 3D 25-fold seismic survey with a bin size of 12 by 12 m and about 12 km(2) of subsurface coverage was acquired in 2005 near a former natural gas storage site west of Berlin, as part of the five-year EU funded CO2SINK project. Main objectives of the seismic survey were to verify earlier geologic interpretations of structure based on vintage 2D seismic and borehole data and to map, if possible, the reservoir pathways in which the CO2 Will be injected at 650 m depth, as well as providing a baseline for future seismic surveys and planning of drilling operations. The uppermost 1000 m are well imaged and show an anticlinal structure with an east-west striking central graben on its top that extendsdown to the target horizon. About 30 m of throw is seen on the bounding faults. No faults are imaged near the planned drill sites. Remnant gas, cushion and residual gas, is present near the top of the anticline in the depth interval of about 250-400 m and has a clear seismic signature; both higher amplitudes in the reservoir horizons and velocity pulldown are observed. Amplitude mapping of these remnant gas horizons shows that they do not extend as far south as the injection site, which is located on the southern flank of the anticline. Amplitude anomalies, gas chimneys along an east-west striking fault, show that the stored or remnant gas either has been or is presently migrating out of the reservoir formations. Summed amplitude mapping of the planned injection horizon indicates that this lithologically heterogeneous formation may be more porous at the injection site.
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| 9. |
- Zhang, Fengjiao, 1981-, et al.
(författare)
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Fracture zones or mafic sills? : Seismic waveform tomography at the Forsmark spent nuclear fuel repository, eastern central Sweden
- 2012
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Ingår i: Society of Exploration Geophysicists. Expanded Abstracts with Biographies. - : Society of Exploration Geophysicists. - 1052-3812. ; , s. 1-5
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish Nuclear Fuel and Waste Management Company (SKB) has been carrying out extensive studies at the Forsmark nuclear waste repository site in the eastern part of central Sweden since 2002. An important component of the studies has been reflection seismic surveys which are useful for locating and characterizing sites for storage of spent nuclear fuel in the crystalline bedrock. Identification of sub-horizontal to gently dipping seismic reflections is especially important since these may represent transport routes for radionuclides. Studies have shown that such reflections can be generated by water filled fracture zones that have a lower velocity than the surrounding bedrock. However, lithological changes, I.e. mafic sills, may also be responsible for reflections in some cases. At the Forsmark site, it is difficult to distinguish fracture zones from mafic sills in the standard reflection seismic processed sections. However, since mafic sills usually have a positive velocity contrast with the background velocity field while fractures zones have a negative one, the two possibilities could be differentiated if we could reconstruct the underground velocity field. Waveform tomography has the potential to perform this reconstruction, and allowing us to discriminate between fractures zones and mafic sills. In this study we test this potential of seismic waveform tomography and conclude that the reflections investigated most likely are generated at low velocity fracture zones.
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| 10. |
- Tsang, Chin-Fu, et al.
(författare)
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Hydrologic testing during drilling : application of the flowing fluid electrical conductivity (FFEC) logging method to drilling of a deep borehole
- 2016
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 24:6, s. 1333-1341
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Tidskriftsartikel (refereegranskat)abstract
- Drilling of a deep borehole does not normally allow for hydrologic testing during the drilling period. It is only done when drilling experiences a large loss (or high return) of drilling fluid due to penetration of a large-transmissivity zone. The paper proposes the possibility of conducting flowing fluid electrical conductivity (FFEC) logging during the drilling period, with negligible impact on the drilling schedule, yet providing important information on depth locations of both high- and low-transmissivity zones and their hydraulic properties. The information can be used to guide downhole fluid sampling and post-drilling detailed testing of the borehole. The method has been applied to the drilling of a 2,500-m borehole at Åre, central Sweden, firstly when the drilling reached 1,600 m, and then when the drilling reached the target depth of 2,500 m. Results unveil eight hydraulically active zones from 300 m down to borehole bottom, with depths determined to within the order of a meter. Further, the first set of data allows the estimation of hydraulic transmissivity values of the six hydraulically conductive zones found from 300 to 1,600 m, which are very low and range over one order of magnitude.
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