Core-log-seismic integration in hard rock environments using the ICDP drilling project COSC-1, Sweden

• Applicants: Professor Dr. Christian Berndt; Dr. Simona Pierdominici
• Subject Area: Palaeontology ; Geophysics
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 339380967

• Final Report Year: 2021

Final Report Abstract

As part of the ICDP priority program “Collisional Orogeny of the Scandinavian Caledonides (COSC)” we studied the geophysical properties of the rocks from the Seve Nappe Complex using the 2.5-kmdeep COSC-1 drill hole (Sweden). Our project had two main objectives. The first geological and geophysical objective was to establish a high-resolution seismic stratigraphy using core-log seismic integration (CLSI) in a metamorphic environment. This involved improving the understanding of the tectonic and structural geologic processes that led to the formation of the Seve Nappe Complex. to determine the extent to which the CLSI method can be applied to metamorphic rocks, although it was developed primarily for hydrocarbon reservoirs in lithified sedimentary rocks. Our study combined data from almost 100 % core recovery, downhole logging, and zero-offset vertical seicmic profile (VSP) with 2D and 3D seismic reflection measurements. First, we analyzed seismic velocities obtained from selected core samples using multisensor core loggers and laboratory analyses. This revealed that microcracks at mineral interfaces generated by pressure relief significantly but variably reduce seismic velocities. As a result, direct correlation of in situ properties with core measurements is not possible for most lithologies. An exception to this is dense, mafic rocks, which appear to be less affected by depressurization. In particular, the analysis of seismic anisotropy in combination with mineralogical composition and microstructural analysis turned out to be a useful tool further on to distinguish lithologic units based on their structural properties. The implementation of the velocity and anisotropy measurements performed in the project into the 3D seismic data processing performed in the last stage of the project resulted in an improved image of the subsurface characterized by better amplitude dynamics and better coherence of the reflectors. This image was then used for a new seismic interpretation of the study area. In another step, we used information from two sets of wireline logs and combined them with the 2D and 3D seismic data, a multi-azimuth walkaway VSP and a high-resolution zero-offset VSP, and combined them through log-seismic integration. Synthetic seismograms were generated from the density and velocity measurements for this purpose, and these were compared with zero-offset seismic traces and seismic traces extracted from the processed surface 3D seismic data at the well site. This showed that the most prominent reflections are caused by amphibolite zones. This means that lithologic inferences can certainly be made from the seismic data through core-log seismic integration. However, detailed extrapolation of acoustic properties measured downhole was not possible, in contrast to applications performed by the oil and gas industry in sedimentary basins. We can attribute this primarily to the much poorer seismic data quality on land, due to difficult terrain conditions, but also to the much larger seismic velocity differences.

Publications

• (2019). Challenges of Core-Log-Seismic Integration in metamorphic environments: A case study for the ICDP drilling project COSC-1, Sweden. Peru. Geophysical Research Abstracts Vol. 21, EGU2019-1306, EGU General Assembly 2019
  Kästner, F., Pierdominici, S., Elger, J., Berndt, C., and Kück, J.
  
• (2020). Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: A case study for the COSC-1 borehole, Sweden, EGU General Assembly 2020, 4–8 May 2020, EGU2020-13955, 2020 (online)
  Kästner, F., Pierdominici, S., Elger, J., Berndt, C., Zappone, A., Kück, J., and Schleicher, A.M.
  
• (2020). Correlation of core and downhole seismic velocities in high-pressure metamorphic rocks: A case study for the COSC-1 borehole, Sweden. Solid Earth, 11(2), 607-626
  Kästner, F., Pierdominici, S., Elger, J., Zappone, A., Kück, J., Berndt C.
  
• (2021). Core-log-seismic integration in metamorphic rocks and its implication for the regional geology: A case study for the ICDP drilling project COSC-1, Sweden. G-Cubed
  Elger, J., Berndt, C., Kästner, F., Pierdominici, S., Kück, J., Almqvist, B.S.G., Juhlin, C., Lorenz, H.
  
• (2021). Core-log-seismic integration in metamorphic rocks at the ICDP drilling project COSC-1, Sweden. Geophysical Research Abstracts, EGU2021-2321, EGU General Assembly 2021
  Elger J., Berndt C., Kästner F., Pierdominici S., Kück J., Almqvist B.S.G., Juhlin C., Lorenz H.
  
• (2021). Seismic anisotropy of metamorphic rocks from the COSC-1 borehole, Sweden: the effects of microstructure and mineral composition. Journal of Geophysical Research-Solid Earth, 126, e2020JB021154
  Kästner, F., Pierdominici, S., Zappone, A., Morales, L.F.G., Schleicher, A.M., Wilke, F.D.H., Berndt, C.
  
• (2021). Seismic anisotropy on metamorphic rocks from the COSC-1 borehole, Sweden: A crossscale investigation from thin section analysis to seismic scales. Geophysical Research Abstracts, EGU2021-12483, EGU General Assembly 2021 (online)
  Kästner F., Pierdominici S., Zappone A., Morales L.F.G., Schleicher A.M., Wilke F.D.H, Berndt C.
  
• Core-log-seismic data integration at the COSC-1 borehole 2 in the Central Scandinavian Caledonides. Phd thesis, Christian-Albrechts-Universität zu Kiel, Kiel, 2021
  Kästner F.