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A geophysical investigation of carbonate build-ups in the Baltic Basin using reflection seismic and well data
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. (Geophysics)ORCID iD: 0000-0001-5082-8365
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During the Late Ordovician, the region around Gotland was part of a shallow epicratonic basin in the southern subtropics. Low latitudes, relatively warm sea temperatures and the presence of a shallow marine environment promoted algae to flourish and diverse carbonate build-ups such as carbonate mounds and reefs developed on the southern margin of Baltica. Locations where these build-ups can be found today include the Palaeozoic sequence beneath the island of Gotland, Sweden and surrounding areas offshore Gotland. Ordovician mud mounds on Gotland were exploited for their hydrocarbon potential during the 1970’s and 1980’s, with large amounts of seismic and well data being acquired by the oil company Oljeprospecketering AB (OPAB). In recent years this largely unpublished dataset has become available for research purposes. Furthermore, the islands of Gotland and Öland have been the target of helicopter-borne electromagnetic investigations conducted by the Geological Survey of Sweden (SGU) (SkyTEM and VLF). Moreover, new seismic reflection data acquired on a research vessel during 2017 complement the OPAB data over certain areas. In published scientific literature, carbonate mounds and reefs have mainly been identified based on outcrops, cuttings samples, cores and wireline logs. Therefore, the extensive seismic and well dataset used in this study provides an opportunity to showcase how large amounts of vintage data can be utilised to generate regional scale attribute maps which can describe geological systems.

In this thesis, the combination of historic seismic and well data, helicopter-borne resistivity data and newly acquired marine seismic data is utilised firstly, to investigate the geometry, distribution and reservoir characteristics of carbonate build-up structures in the Gotland area. Secondly, we generate detailed depth and thickness maps of the Ordovician formation in the subsurface of Gotland based on the seismic data. Thirdly, a detailed interpretation of a 3D seismic dataset acquired over a mound structure on Gotland and a scoping assessment of the potential to utilize these mud mounds for subsurface compressed air energy storage (CAES) is performed. Finally, an automating refraction velocity analysis in the marine seismic data is used to generate a basement velocity map over a large portion of the Swedish sector of the Baltic Sea. 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 63
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1866
Keywords [en]
Reflection seismic, Ordovician, Silurian, Carbonate mud mounds, Reefs, Gotland, Sweden, CAES, Seismic interpretation, OPAB dataset, 3D seismic
National Category
Geophysics
Research subject
Geophysics with specialization in Solid Earth Physics
Identifiers
URN: urn:nbn:se:uu:diva-393043ISBN: 978-91-513-0780-0 (print)OAI: oai:DiVA.org:uu-393043DiVA, id: diva2:1360401
Public defence
2019-11-29, Hambergsalen, Geocentrum, Villavägen, 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2019-11-08 Created: 2019-10-12 Last updated: 2019-11-27
List of papers
1.
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2. Investigation of an Ordovician carbonate mound beneath Gotland, Sweden, using 3D seismic and well data
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: 2019-10-12
3. Geophysical mapping of Silurian reefs offshore and onshore Gotland, Sweden
Open this publication in new window or tab >>Geophysical mapping of Silurian reefs offshore and onshore Gotland, Sweden
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-394279 (URN)
Available from: 2019-10-12 Created: 2019-10-12 Last updated: 2019-10-22

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