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This study was undertaken to quantify and evaluate the density and porosity characteristics of a Boda Claystone Formation (BCF) core sample using medical CT. Each voxel of the 3D CT volume was described with three variables: dry CT number, saturated CT number, and effective porosity. Disparity pore voxels were revealed using the genetic groups’ algorithm of data-mining techniques. The K-fold cross-validation algorithm has been applied to determine the number of the most stable cluster. The 3D spatial distributions of voxel-porosity by rock constituents, as well as the 3D distribution of porosity clusters by rock components, were found by Boolean function implementation. The terrigenous detrital fragments had the lowest porosity mean (0.16%) and highest coefficient variation value (1039.39%). While the Fine siltstone component had the highest porosity mean (3.39%) and lower coefficient of variation (134.99%). The difference in the variation of coefficient proportions is related to the outlier ratios in each rock component. Independently of both the rock types and the sedimentary structures, two clusters could be defined: one for the micro-porosity and one for the macro-porosity regimes. The former showed a continuous 3D spatial appearance, while the latter appeared in patches. These patches may also be connected, at least partly, to some local smectite aggregates. These clay minerals could lose their structured water content during vacuuming and swell when adsorbing water during sample saturation. In each rock type, the micro-porosity regime could be related to low-density rock fragments. The mean effective porosity of the micro-pore regime was about 0.02, which corresponds to the petrophysical core measurements. For the macro regimes, the average was 0.1.

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.

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The Tótkomlós Calcareous Marl (TCM), a Member of the Late Miocene Endrőd Formation was investigated as a potential cap and source rock and also as a local tight reservoir in the Pannonian Basin. Only a limited dataset is available for petrophysical characterisation of this formation. The study reports on a complex measurement campaign performed on three core triplet samples of the Tótkomlós Calcareous Marl, including pore structure and petrophyiscal analysis at various pressure conditions. Direct laboratory measurements of compressional (P) and shear (S) wave velocities on oriented rock samples provide information about the anisotropic behaviour of the studied samples. A quantitative description of seismic anisotropy can improve the quality of seismic data processing. Pore structure investigations indicated plate-like materials with a typical pore throat size between 75-110 nm. Gas permeability measurements showed very low permeability values in the order of magnitude between 10-16-10-18 m 2. Weak acoustic anisotropy is observed both for P-and Swaves. Decreasing anisotropy with increasing confining pressure indicated that the samples become less anisotropic with increasing effective stress. the shallow water facies (Figure 2. represents approximately the palaeo-geomorphology on which deposition of the calcareous marl occurred). Their colour is generally yellowish grey to grey, mainly massive, but sometimes laminated, occasionally organic rich bands, layers of few-ten centimetres scale carbonate rich sandstone layers are interbedded with the monotonous calcare ous marl in the core samples (Figure 3).