Seismic and mechanical properties of Opalinus Clay: comparison between sandy and shaly facies from Mont Terri (Switzerland)

Experimental Deformation of Opalinus Clay at Elevated Temperature and Pressure Conditions: Mechanical Properties and the Influence of Rock Fabric

“…The sedimentary, compaction and burial history of OPA led to a sub-parallel arrangement of clay platelets with respect to macroscopic bedding (Wenk et al 2008). Due to this and the heterogeneity of macro-and microfabric in OPA, hydrological, microstructural, mechanical and transport-related properties exhibit transverse isotropy (e.g., NAGRA 2002;VanLoon et al 2004;Plischke 2010, 2011;Keller et al 2011Keller et al , 2013bSiegesmund et al 2014;Keller and Holzer 2018). Porosity estimates depend on resolution of the respective method, ranging between 4.9 and 19.1vol% with best porosity estimates of 18 vol% and 11.1 vol% for the shaly and sandy facies, respectively.…”

“…Our observation that samples taken from the sandy facies are stronger with higher elastic moduli (Figs. 4,12) is consistent with previous studies (cf., Popp and Salzer 2007;Plischke 2010, 2011;Amann et al 2011Amann et al , 2012Vöbel et al 2014;Siegesmund et al 2014;Wild and Amann 2018;Favero et al 2018;Giger et al 2018;Zhang and Laurich 2019;Minardi et al 2020).…”

“…These factors include diagenetic processes influenced by chemical reactions, mechanical loading and temperature variations (Gutierrez et al 1996;Bjørlykke and Høek 1997;Nygård et al 2004;Wenk et al 2008;Ilgen et al 2017;Morley et al 2017). Additionally, shales display an increased crystallographic and shape-preferred orientation of phyllosilicates, resulting in a distinct anisotropy of physical and mechanical properties related to the depositional and diagenetic conditions, mineral composition and thermal maturity (e.g., Chiarelli et al 2000;Wenk et al 2008;Sone and Zoback 2013;Siegesmund et al 2014;Liu et al 2018). Previous experimental studies show that the strength and elastic properties of clay-rich rocks depend on applied confining pressure (e.g., Ibanez and Kronenberg 1993;Niandou et al 1997;Petley 1999;Naumann et al 2007;Herrmann et al 2018), temperature (e.g., Zhang et al 2007;Masri et al 2014;Rybacki et al 2015;Liu et al 2019), strain rate (e.g., Swan et al 1989;Chong and Boresi 1990;Kwon and Kronenberg 1994;Al-Bazali et al 2008;Bonnelye et al 2017a, b;Hou et al 2019), and water content (e.g., Valès et al 2004;Zhang et al 2012;Wild et al 2015;Zhang and Laurich 2019).…”

“…For the safety assessment of OPA as a potential repository formation, prior laboratory deformation experiments have mainly focused on the characterization of the anisotropic and hydro-mechanically coupled behavior related to the excavation processes as well as on the determination of effective strength and stiffness parameters of the homogeneous, clay-rich shaly facies (e.g., Corkum and Martin 2007;Naumann et al 2007;Popp and Salzer 2007;Amann et al 2011Amann et al , 2012Wild et al 2015;Zhang et al 2017;Favero et al 2018;Giger et al 2018;Orellana et al 2018Orellana et al , 2019Wild and Amann 2018;Minardi et al 2020). However, due to its higher elastic moduli, the sandy facies has recently gained importance in research (Kaufhold et al 2013(Kaufhold et al , 2016Siegesmund et al 2014;Minardi et al 2016;Jaeggi et al 2017;Zhang and Laurich 2019). The sandy facies of OPA displays a pronounced, fabric related heterogeneity that is characterized by an alternated bedding of quartz-and clay-rich layers (Peters et al 2011;Kaufhold et al 2013;Houben et al 2014).…”

Quantification of Lithological Heterogeneity Within Opalinus Clay: Toward a Uniform Subfacies Classification Scheme Using a Novel Automated Core Image Recognition Tool

“…Many studies at Mont Terri have emphasized the tight relations between various rock properties, lithology and texture. Typical examples include the small-scale heterogeneity of geomechanical properties (Klinkenberg et al, 2009;Kaufhold et al, 2013;Siegesmund et al, 2014), the distribution of micro-porosity (Houben et al, 2013(Houben et al, , 2014Keller et al, 2013;Philipp et al, 2017), sorption processes and radionuclides diffusive transport (Hennig et al, 2020;Hennig and Kühn, 2021), the responses of seismic P-wave velocity (Kneuker et al, 2017;Schuster et al, 2017;Lauper et al, 2018), and more generally, the overall (geochemical, petrophysical and hydro-mechanical) anisotropic behavior of the OPA (Van Loon et al, 2004;Wenk et al, 2008;Favero et al, 2018). Jaeggi and Bossart (2014) provide an overview of the main rock properties (petrophysical, hydrogeological, rock mechanical, thermic, geochemical/pore water composition, and gas entry pressure parameters) of the OPA at Mont Terri and their relationship with lithology.…”