New results of Boda Claystone research: Genesis, mineralogy, geochemistry, petrophysics

Abstract

Boda Claystone is a very tight clayey rock with extreme low porosity and permeability, nano-size pores and small amounts of swelling clays. Due to this character it is ideal as a potential host rock for research into the possibilities of high-level waste deposition in geological formation. Though the research started more than 30 years ago, the genesis, the geotectonic history of the Boda Claystone Formation (BCF) and the geology of surrounding areas has only been sketched out recently. On the basis of research of the past few years the process of sedimentation of different blocks was able to be reconstructed. Equipment and methodological developments were needed for the investigation of reservoir geological and hydrodynamic behaviour of this rock, which began in the early 2000s. Based on them the pore structure and reservoir could be characterized in detail. Only theoretical approaches were available for the chemical composition of free porewater. Traditional water-extracting methods were not adaptable because of excessively low porosity and nano-scale pore size distribution. Hence, new ways have to be found for getting enough water for analysis. These new results of BCF research help to prepare more sophisticated and directed experiments, in which there is a great interest internationally.

Multiple roles of clays in radioactive waste confinement – introduction

“…Although the national programme research started more than 30 years ago, the genesis, the geotectonic history of the Boda Claystone Formation (BCF) and the geology of surrounding areas has only been sketched out recently. Fedor et al (2018) report recent research, including advances in equipment and methodological developments, that have been progressed; these new results of BCF research help in the preparation of more sophisticated and directed experiments, in which there is a great interest internationally.…”

Application of a CNN to the Boda Claystone Formation for high-level radioactive waste disposal

“…However, the presence of tectonic fractures somewhat modulates the latter 11 . The mineral and chemical composition of the BCF are excellent fluid flow inhibitors because the presence of swelling clay minerals results in the fractures possessing a natural self-sealing capability 14 , 15 . Nevertheless, fractures and inhomogeneities can still pose risks when transporting radioactive materials 14 , 16 , 17 .…”

Quantifying variability of physical /petrophysical properties of Boda Claystone Formation (BCF) using X-ray computed-tomography scan images (CT)

“…(5-30 wt%), albite (20-60 wt%), carbonate minerals (calcite and dolomite; 10-50 wt%) and hematite (5-10 wt%) (Máthé 1998(Máthé , 2015Árkai et al 2000;Fedor et al, 2018). The absolute dominant clay mineral is illite-muscovite (15-50 wt%), with chlorite (0-35 wt%) as another determinant clay mineral phase; smectite, kaolinite, vermiculite and mixed-layer clay minerals (illite/ smectite, chlorite/smectite) being identified in minor amounts (Máthé 1998(Máthé , 2015Árkai et al 2000;Varga et al 2005Varga et al , 2006.…”

“…The absolute dominant clay mineral is illite-muscovite (15-50 wt%), with chlorite (0-35 wt%) as another determinant clay mineral phase; smectite, kaolinite, vermiculite and mixed-layer clay minerals (illite/ smectite, chlorite/smectite) being identified in minor amounts (Máthé 1998(Máthé , 2015Árkai et al 2000;Varga et al 2005Varga et al , 2006. In the greyish black siltstones and claystone interstratification, the illite-muscovite content decreases, and the chlorite becomes the dominant mineral (e.g., Fedor et al, 2018). Jámbor (1964) was the first to describe the formation and interpret it as lacustrine sediment.…”

“…Otherwise, petrological and geochemical analyses of Boda block, i.e., dominantly albite, crystals of dolomite layers are pseudomorphs after 'Hopper halite, desiccation cracks, and high Na2O contents, proved that the BCF was deposited in halite-and sulfate-dominated, long-lived perennial and ephemeral inland saline lakes surrounded by saline and dry mudflats and distal alluvial deposits, under semi-arid to arid climatic conditions Máthé 1998;Árkai et al 2000;Varga et al 2005;Máthé & Varga 2012;Fedor et al, 2018). In comparison, the absence of dolomite layers, analcime dominant, and lacking (pseudomorphs after halite) deposits in Gorica block, suggest that the lake environment was moderately saline-alkaline (Remmy & Ferrell 1989;Máthé 2015).…”