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García Juanatey, M. d., Hübert, J., Tryggvason, A., Juhlin, C., Pedersen, L. B., Bauer, T. E. & Dehghannejad, M. (2019). 2D and 3D MT in the central Skellefte Ore District, northern Sweden. Tectonophysics, 764, 124-138
Open this publication in new window or tab >>2D and 3D MT in the central Skellefte Ore District, northern Sweden
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2019 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 764, p. 124-138Article in journal (Refereed) Published
Abstract [en]

New broadband magnetotelluric (MT) data have been acquired along two parallel profiles in the central part of the metallogenic Skellefte district in northern Sweden. The data were recorded as part of the Swedish 4D modelling of mineral belts project and cover an area with several economical and sub-economical deposits. The dimensionality and quality of the data were carefully analyzed and new error floors were systematically determined prior to inverse modelling in 2D and 3D. The algorithms used were EMILIA and WSINV3DMT. For the 2D inversion, only the determinant of the impedance tensor was used, while for the 3D inversion all elements were considered. The obtained models fit the inverted data, and image the main regional features. A detailed comparison reveals the superiority of the 3D model, both in model structures and data fit. After assessing the main features in the model, an interpretation is proposed and refined with the support of previous geophysical studies. The most interesting features are large and medium-sized conductors associated with crustal-scale shear zones and faults within the Skellefte Group rocks. These may be depicting a network of fossil pathways for hydrothermal fluid transport and as such, provide new insight into past processes in the area.

Keywords
Magnetotellurics, 3D inversion, Deep exploration, Brownfield, Shear zones, Mineral systems
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
urn:nbn:se:uu:diva-178057 (URN)10.1016/j.tecto.2019.04.003 (DOI)000472697900008 ()
Projects
VINNOVA 4D modeling of mineral belts
Funder
Vinnova
Available from: 2012-07-26 Created: 2012-07-26 Last updated: 2019-08-16Bibliographically approved
Buntin, S., Malehmir, A., Koyi, H., Högdahl, K., Malinowski, M., Larsson, S. A., . . . Gorszczyk, A. (2019). Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield. Scientific Reports, 9, Article ID 10498.
Open this publication in new window or tab >>Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 10498Article in journal (Refereed) Published
Abstract [en]

Saucer-shaped intrusions of tens of meters to tens of kilometres across have been observed both from surface geological mapping and geophysical observations. However, there is only one location where they have been reported to extend c. 100 km laterally, and emplaced both in a sedimentary basin and the crystalline basement down to 12 km depth. The legacy BABEL offshore seismic data, acquired over the central Fennoscandian Shield in 1989, have been recovered and reprocessed with the main goal of focusing on this series of globally unique crustal-scale saucer-shaped intrusions present onshore and offshore below the Bothnian Sea. The intrusions (c. 1.25 Ga), emplaced in an extensional setting, are observed within both sedimentary rocks (<1.5 Ga) and in the crystalline basement (>1.5 Ga). They have oval shapes with diameters ranging 30-100 km. The reprocessed seismic data provide evidence of up-doming of the lower crust (representing the melt reservoir) below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels. We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses (c. 100-300 m). Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-391379 (URN)10.1038/s41598-019-46837-x (DOI)000476468700026 ()31324841 (PubMedID)
Funder
Swedish Research Council, 2015-05177
Available from: 2019-09-03 Created: 2019-09-03 Last updated: 2019-09-03Bibliographically approved
Sopher, D., Juhlin, C., Levendal, T., Erlstrom, M., Nilsson, K. & Da Silva Soares, J. P. (2019). Evaluation of the subsurface compressed air energy storage (CAES) potential on Gotland, Sweden. Environmental Earth Sciences, 78(6), Article ID 197.
Open this publication in new window or tab >>Evaluation of the subsurface compressed air energy storage (CAES) potential on Gotland, Sweden
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2019 (English)In: Environmental Earth Sciences, ISSN 1866-6280, E-ISSN 1866-6299, Vol. 78, no 6, article id 197Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Faludden reservoir, OPAB data set, Gas storage, Baltic Basin, Baltic Sea, Wind power
National Category
Other Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-380480 (URN)10.1007/s12665-019-8196-1 (DOI)000460829600006 ()
Funder
Swedish Research Council, 2010-3657
Available from: 2019-04-15 Created: 2019-04-15 Last updated: 2019-04-15Bibliographically approved
Levendal, T., Sopher, D., Juhlin, C. & Lehnert, O. (2019). Investigation of an Ordovician carbonate mound beneath Gotland, Sweden, using 3D seismic and well data. Journal of Applied Geophysics, 162, 22-34
Open this publication in new window or tab >>Investigation of an Ordovician carbonate mound beneath Gotland, Sweden, using 3D seismic and well data
2019 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 162, p. 22-34Article in journal (Refereed) Published
Abstract [en]

The Swedish island of Gotland is located within the Baltic Basin. During the Late Ordovician the region around Gotland was part of a shallow epicratonic basin in the southern subtropics. In these warm-water environments algae flourished, diverse reefs developed close to the coastline and further outboard carbonate mounds developed. These mounds formed rigid high relief structures surrounded by fine-grained siliciclastics and marls and can be detected on seismic images as isolated concave upwards features. The sedimentary succession beneath Gotland was intensely investigated in the 1970s and 1980s for its hydrocarbon potential, and subsequently, oil was commercially produced from reservoirs within Ordovician mounds. In 1981, a 3D seismic survey was conducted by Horizon Exploration Ltd. over the Fardume mound on northern Gotland. To date no results from these 3D data have been published in scientific literature.

The region of Gotland aims to produce 100% of its energy from renewable sources and currently much of Gotland's electricity is provided by wind turbines. Due to the intermittent nature of wind power, one solution to regulate the supply of electricity from wind energy is Compressed Air Energy Storage (CAES).

In this study, we convert the 3D seismic survey acquired over the Fardume mound from scanned TIFF images to SEGY format. These data are then utilized together with well data to gain a better knowledge of the geological structure of the mound and to examine its reservoir characteristics and potential for CAES. To date, carbonate mounds on Gotland have mainly been reported in the scientific literature using well data. This 3D seismic survey, therefore, provides a rare opportunity to better characterize and investigate the structure of one of the carbonate mounds on Gotland.

Keywords
Sweden, Gotland, Carbonate mounds, Late Ordovician, OPAB dataset, Seismic interpretation, 3D seismic, CAES
National Category
Geophysics Geology
Identifiers
urn:nbn:se:uu:diva-383000 (URN)10.1016/j.jappgeo.2019.01.008 (DOI)000465056200003 ()
Funder
Swedish Research CouncilGerman Research Foundation (DFG), LE 867/8-1German Research Foundation (DFG), LE 867/8-2
Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-21Bibliographically approved
Levendal, T. C., Lehnert, O., Sopher, D., Erlström, M. & Juhlin, C. (2019). Ordovician carbonate mud mounds of the Baltoscandian Basin in time and space - A geophysical approach. Palaeogeography, Palaeoclimatology, Palaeoecology, 535, Article ID 109345.
Open this publication in new window or tab >>Ordovician carbonate mud mounds of the Baltoscandian Basin in time and space - A geophysical approach
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2019 (English)In: Palaeogeography, Palaeoclimatology, Palaeoecology, ISSN 0031-0182, E-ISSN 1872-616X, Vol. 535, article id 109345Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Baltica, Carbonate mud mounds, Gotland, OPAB dataset, Seismic interpretation, Sweden
National Category
Earth and Related Environmental Sciences Geophysics
Identifiers
urn:nbn:se:uu:diva-393044 (URN)10.1016/j.palaeo.2019.109345 (DOI)
Available from: 2019-09-17 Created: 2019-09-17 Last updated: 2019-09-20Bibliographically approved
Beckel, R. A. & Juhlin, C. (2019). The cross-dip correction as a tool to improve imaging of crooked-line seismic data: a case study from the post-glacial Burtrask fault, Sweden. Solid Earth, 10(2), 581-598
Open this publication in new window or tab >>The cross-dip correction as a tool to improve imaging of crooked-line seismic data: a case study from the post-glacial Burtrask fault, Sweden
2019 (English)In: Solid Earth, ISSN 1869-9510, E-ISSN 1869-9529, Vol. 10, no 2, p. 581-598Article in journal (Refereed) Published
Abstract [en]

Understanding the development of post-glacial faults and their associated seismic activity is crucial for risk assessment in Scandinavia. However, imaging these features and their geological environment is complicated due to special challenges of their hardrock setting, such as weak impedance contrasts, often high noise levels and crooked acquisition lines. A crooked-line geometry can cause time shifts that seriously de-focus and deform reflections containing a cross-dip component. Advanced processing methods like swath 3-D processing and 3-D pre-stack migration can, in principle, handle the crooked-line geometry but may fail when the noise level is too high. For these cases, the effects of reflector cross-dip can be compensated for by introducing a linear correction term into the standard processing flow. However, existing implementations of the cross-dip correction rely on a slant stack approach which can, for some geometries, lead to a duplication of reflections. Here, we present a module for the cross-dip correction that avoids the reflection duplication problem by shifting the reflections prior to stacking. Based on tests with synthetic data, we developed an iterative processing scheme where a sequence consisting of cross-dip correction, velocity analysis and dip-moveout (DMO) correction is repeated until the stacked image converges. Using our new module to reprocess a reflection seismic profile over the post-glacial Burtrask fault in northern Sweden increased the image quality significantly. Strike and dip information extracted from the cross-dip analysis helped to interpret a set of southeast-dipping reflections as shear zones belonging to the regional-scale Burtrask Shear Zone (BSZ), implying that the BSZ itself is not a vertical but a southeast-dipping feature. Our results demonstrate that the cross-dip correction is a highly useful alternative to more sophisticated processing methods for noisy datasets. This high-lights the often underestimated potential of rather simple but noise-tolerant methods in processing hardrock seismic data.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-383512 (URN)10.5194/se-10-581-2019 (DOI)000466424700001 ()
Available from: 2019-05-16 Created: 2019-05-16 Last updated: 2019-05-16Bibliographically approved
Ghosal, D. & Juhlin, C. (2018). Estimation of dispersion attributes at seismic frequency-a case study from the Frigg-Delta reservoir, North sea. Journal of Geophysics and Engineering, 15(5), 1799-1810
Open this publication in new window or tab >>Estimation of dispersion attributes at seismic frequency-a case study from the Frigg-Delta reservoir, North sea
2018 (English)In: Journal of Geophysics and Engineering, ISSN 1742-2132, E-ISSN 1742-2140, Vol. 15, no 5, p. 1799-1810Article in journal (Refereed) Published
Abstract [en]

Estimation of the reservoir physical parameters in hydrocarbon zones is important for seismic exploration. Frequency analysis has proven to provide useful information on the velocity dispersion and attenuation of seismic wave-fields propagating through porous media. In this study we have carried out a velocity and reflectivity dispersion analysis using borehole and post-stack angle dependent seismic datasets from the Frigg-Delta reservoir in the North Sea. Rock physics analysis using borehole datasets indicate that in the seismic frequency range (1-100 Hz) dispersion maxima appear at similar to 5 Hz frequency, assuming an oil saturation associated with the reservoir ranging between 40% and 60%, porosity as 30% and permeability as 1 Darcy. Moreover, the P-wave velocity (V-p) dispersion is estimated similar to 5 times less for the high oil saturation in the upper part of the reservoir compared to that for low oil saturation in the deeper part of the reservoir. Dispersion analysis on the angle dependent seismic migrated sections is carried out by inverting spectrally decomposed isofrequency sections using a least squares algorithm. The inverted results show that the top of the reservoir is more clearly demarcated at low frequency (similar to 7Hz) than at higher frequencies.

Keywords
velocity dispersion, WIFF, normal incidence, spectral decomposition, Frigg-Delta
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-357674 (URN)10.1088/1742-2140/aabb35 (DOI)000434383900001 ()
Available from: 2018-08-22 Created: 2018-08-22 Last updated: 2018-08-22Bibliographically approved
Muhamad, H., Juhlin, C., Malehmir, A. & Sopher, D. (2018). Integrated interpretation of geophysical data of the Paleozoic structure in the northwestern part of the Siljan Ring impact crater, central Sweden. Journal of Applied Geophysics, 148, 201-215
Open this publication in new window or tab >>Integrated interpretation of geophysical data of the Paleozoic structure in the northwestern part of the Siljan Ring impact crater, central Sweden
2018 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 148, p. 201-215Article in journal (Refereed) Published
Abstract [en]

The Siljan Ring impact structure is the largest known impact structure in Europe and is Late Devonian in age. It contains a central uplift that is about 20-30 km in diameter and is surrounded by a ring-shaped depression. The Siljan area is one of the few areas in Sweden where the Paleozoic sequence has not been completely eroded, making it an important location for investigation of the geological and tectonic history of Baltica during the Paleozoic. The Paleozoic strata in this area also provide insight into the complex deformation processes associated with the impact. In this study we focus on the northwestern part of the Siljan Ring, close to the town of Orsa, with the main objective of characterizing the subsurface Paleozoic succession and uppermost Precambrian crystalline rocks along a series of seismic reflection profiles, some of which have not previously been published. We combine these seismic data with gravity and magnetic data and seismic traveltime tomography results to produce an integrated interpretation of the subsurface in the area. Our interpretation shows that the Paleozoic sequence in this area is of a relatively constant thickness, with a total thickness typically between 300 and 500 m. Faulting appears to be predominantly extensional, which we interpret to have occurred during the modification stage of the impact. Furthermore, based on the geophysical data in this area, we interpret that the impact related deformation to differ in magnitude and style from other parts of the Siljan Ring.

National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-311546 (URN)10.1016/j.jappgeo.2017.10.001 (DOI)000424171900019 ()
Available from: 2016-12-28 Created: 2016-12-28 Last updated: 2018-03-28Bibliographically approved
Ivandic, M., Bergmann, P., Kummerow, J., Huang, F., Juhlin, C. & Lueth, S. (2018). Monitoring CO2 saturation using time-lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO2 storage pilot site, Germany. Geophysical Prospecting, 66(8), 1568-1585
Open this publication in new window or tab >>Monitoring CO2 saturation using time-lapse amplitude versus offset analysis of 3D seismic data from the Ketzin CO2 storage pilot site, Germany
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2018 (English)In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 66, no 8, p. 1568-1585Article in journal (Refereed) Published
Abstract [en]

The injection of CO2 at the Ketzin pilot site commenced in June 2008 and was terminated in August 2013 after 67 kT had been injected into a saline formation at a depth of 630-650 m. As part of the site monitoring program, four 3D surface seismic surveys have been acquired to date, one baseline and three repeats, of which two were conducted during the injection period, and one during the post-injection phase. The surveys have provided the most comprehensive images of the spreading CO2 plume within the reservoir layer. Both petrophysical experiments on core samples from the Ketzin reservoir and spectral decomposition of the 3D time-lapse seismic data show that the reservoir pore pressure change due to CO2 injection has a rather minor impact on the seismic amplitudes. Therefore, the observed amplitude anomaly is interpreted to be mainly due to CO2 saturation. In this study, amplitude versus offset analysis has been applied to investigate the amplitude versus offset response from the top of the sandstone reservoir during the injection and post-injection phases, and utilize it to obtain a more quantitative assessment of the CO2 gaseous saturation changes. Based on the amplitude versus offset modelling, a prominent decrease in the intercept values imaged at the top of the reservoir around the injection well is indeed associated solely with the CO2 saturation increase. Any change in the gradient values, which would, in case it was positive, be the only signature induced by the reservoir pressure variations, has not been observed. The amplitude versus offset intercept change is, therefore, entirely ascribed to CO2 saturation and used for its quantitative assessment. The estimated CO2 saturation values around the injection area in the range of 40%-60% are similar to those obtained earlier from pulsed neutron-gamma logging. The highest values of 80% are found in the second seismic repeat in close vicinity to the injection and observation wells.

Place, publisher, year, edition, pages
WILEY, 2018
Keywords
CO2 sequestration, 3D time lapse (4D), Seismic monitoring, AVO, CO2 saturation
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-366944 (URN)10.1111/1365-2478.12666 (DOI)000445183300009 ()
Funder
EU, FP7, Seventh Framework Programme
Available from: 2018-11-29 Created: 2018-11-29 Last updated: 2018-11-29Bibliographically approved
Xu, Z., Sopher, D., Juhlin, C., Han, L. & Gong, X. (2018). Radon-domain interferometric interpolation for reconstruction of the near-offset gap in marine seismic data. Journal of Applied Geophysics, 151, 125-141
Open this publication in new window or tab >>Radon-domain interferometric interpolation for reconstruction of the near-offset gap in marine seismic data
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2018 (English)In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 151, p. 125-141Article in journal (Refereed) Published
Abstract [en]

In towed marine seismic data acquisition, a gap between the source and the nearest recording channel is typical. Therefore, extrapolation of the missing near-offset traces is often required to avoid unwanted effects in subsequent data processing steps. However, most existing interpolation methods perform poorly when extrapolating traces. Interferometric interpolation methods are one particular method that have been developed for filling in trace gaps in shot gathers. Interferometry-type interpolation methods differ from conventional interpolation methods as they utilize information from several adjacent shot records to fill in the missing traces. In this study, we aim to improve upon the results generated by conventional time-space domain interferometric interpolation by performing interferometric interpolation in the Radon domain, in order to overcome the effects of irregular data sampling and limited source-receiver aperture. We apply both time-space and Radon-domain interferometric interpolation methods to the Sigsbee2B synthetic dataset and a real towed marine dataset from the Baltic Sea with the primary aim to improve the image of the seabed through extrapolation into the near-offset gap. Radon-domain interferometric interpolation performs better at interpolating the missing near offset traces than conventional interferometric interpolation when applied to data with irregular geometry and limited source-receiver aperture. We also compare the interferometric interpolated results with those obtained using solely Radon transform (RT) based interpolation and show that interferometry-type interpolation performs better than solely RT-based interpolation when extrapolating the missing near-offset traces. After data processing, we show that the image of the seabed is improved by performing interferometry-type interpolation, especially when Radon-domain interferometric interpolation is applied.

Keywords
Interferometric interpolation, Cross-correlation, Multiple, Near-offset gap, Radon transform
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-354247 (URN)10.1016/j.jappgeo.2018.02.012 (DOI)000430903200012 ()
Available from: 2018-06-29 Created: 2018-06-29 Last updated: 2018-06-29Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0003-2776-0846

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