Affiliation:
1. Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences , Telegrafenberg, 14473 Potsdam, Germany
2. Technical University Berlin , Ernst-Reuter-Platz 1, 10587 Berlin, Germany
Abstract
SUMMARY
Low permeability, high retention capacity and self-sealing ability are advantageous characteristics that are attributed to argillaceous rocks. In contrast, other properties of clay, such as internal heterogeneities, strong attenuation and anisotropic behaviour, pose major challenges for underground exploration techniques. Although with regard to the underground storage of nuclear waste, the seismic exploration in the underground itself is of great importance to fill the gap between surface and borehole investigations. Furthermore, to prevent destruction of the host rock during exploration this demands low to non-invasive techniques. To approach these issues, a seismic survey was carried out in the Mont Terri Underground Rock Laboratory (Switzerland) using a gallery-based acquisition with an operating range up to several decametres. The seismic campaign included three-component borehole sensors and two different seismic source types (pneumatic impact and magnetostrictive vibroseis source). An executed source comparison analysed the characteristics of the different source types, for example frequency or amplitude behaviour of the generated wavefield, to assess their performance under similar conditions at the meso scale and to reveal their strengths and weaknesses in clay. Based on these findings, we performed traveltime and reflection analyses that demonstrate their potential to characterize clay formations and to map internal structures.
The highest seismic velocities are found in the carbonate-rich sandy facies (vPmax = 4000 m s−1, vSmax = 2050 m s−1), slower velocities are found in the sandy facies (vPmax = 3720 m s−1, vSmax = 1840 m s−1) and the slowest velocities are found in the shaly facies (vPmax = 3220 m s−1, vSmax = 1480 m s−1). The seismic velocity anisotropy is larger within the shaly facies (AvP = 23 per cent, AvS = 32 per cent) compared to the sandy facies (AvP = 9 per cent, AvS = 12 per cent) and it is more pronounced for S-waves than P-waves. Thus, non-invasive meso-scale seismic techniques are suited to characterize the Opalinus Clay in great detail.
Funder
Federal Ministry of Education and Research
Helmholtz Association
GFZ
Publisher
Oxford University Press (OUP)
Subject
Geochemistry and Petrology,Geophysics
Reference60 articles.
1. Digitization in mechanized tunnelling technology;Bäppler,2018
2. The velocity of compressional waves in rocks to 10 kilobars, Part II;Birch;J. geophys. Res.,1961
3. RA experiment: updated review of the rock mechanics properties of the opalinus clay of the Mont Terri URL based on laboratory and field testing;Bock,2009
4. Rayleigh-to-shear wave conversion at the tunnel face - From 3D-FD modeling to ahead-of-drill exploration;Bohlen;Geophysics,2007
5. Mont Terri rock laboratory, 20 years of research: introduction, site characteristics and overview of experiments;Bossart;Swiss J. Geosci.,2017
Cited by
2 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献