Tivadar M. Tóth

GraphClus, a MATLAB program for cluster analysis using graph theory

Cluster analysis is used in numerous scientific disciplines. A method of cluster analysis based on graph theory is discussed and a MATLAB(TM) code for its implementation is presented. The algorithm is based on the number of variables that are similar between samples. By changing the similarity criterion in a stepwise fashion, a hierarchical group structure develops, and can be displayed by a dendrogram. Three indexes describe the homogeneity of a given variable in a group, the heterogeneity of that variable between two groups, and the usefulness of that variable in distinguishing two groups. The algorithm is applied to both a synthetic dataset and a set of trace element analyses of lavas from Mount Etna in order to compare GraphClus to other cluster analysis algorithms.

Refinement of genetic and structural models of the Úrkút manganese ore deposit (W-Hungary, Europe) using statistical evaluation of archive data

Although the Úrkút manganese ore deposit in western placecountry-regionHungary has been exploited for at least 90 years, there are still numerous open questions concerning ore genetics as well as structure and geometry of the ore body. A large set of available archive data for the deposit have been reviewed and evaluated in order to solve some of the most crucial problems. For processing, besides diverse GIS approaches, univariate and multivariate statistical methods were used on the created unified database. The main aims of the mathematical treatment were giving a classification scheme for the wide spectrum of Mn-ores based on their chemical composition (Mn, Fe, Si, P) as well as evaluation of their spatial distribution. For the ore characterization and understanding the genetic processes, cluster and discriminant function analyses were used. Results of the multivariate treatment verified the existence of different ore types and provided an exact chemical definition for all of them. It alsoinferred that the main geochemical processes that took place in ore genesis were similar for all sample groups (ore types) with significantly different weights in each case.A 3D evaluation of the Úrkút mine heading map system shows that the ore body covers the footwall surface as a stratiform sheet throughout the study area. Palaeo-relief studies suggest a significant difference between the footwall and hanging wall morphologies which clearly implies tectonic activity following ore deposition. The deposit was affected by an E-W compression stress field near the Aptian-Albian transition causing folding of the Mn deposit.

Integrated petrographic – rock mechanic borecorestudy from the metamorphic basement of thePannonian Basin, Hungary

Abstract The integrated evaluation of borecores from the Mezősas-Furta fractured metamorphic hydrocarbon reservoir suggests significantly distinct microstructural and rock mechanical features within the analysed fault rock samples. The statistical evaluation of the clast geometries revealed the dominantly cataclastic nature of the samples. Damage zone of the fault can be characterised by an extremely brittle nature and low uniaxial compressive strength, coupled with a predominately coarse fault breccia composition. In contrast, the microstructural manner of the increasing deformation coupled with higher uniaxial compressive strength, strain-hardening nature and low brittleness indicate a transitional interval between the weakly fragmented damage zone and strongly grinded fault core. Moreover, these attributes suggest this unit is mechanically the strongest part of the fault zone. Gougerich cataclasites mark the core zone of the fault, with their widespread plastic nature and locally pseudo-ductile microstructure. Strain localization tends to be strongly linked with the existence of fault gouge ribbons. The fault zone with ∼15 m total thickness can be defined as a significant migration pathway inside the fractured crystalline reservoir. Moreover, as a consequence of the distributed nature of the fault core, it may possibly have a key role in compartmentalisation of the local hydraulic system.

Structural controls on petroleum migration and entrapment within the faulted basement blocks of Szeghalom Dome (Pannonian Basin, SE Hungary)

The basement of the Pannonian Basin contains several fractured metamorphic hydrocarbon reservoirs that typically form structural highs between the Neogene sedimentary sub-basins. One of the largest reservoirs, the Szeghalom Dome, is located on the northern margin of the Bekes Basin and is mainly composed of Variscan gneisses and amphibolites with different metamorphic evolutions. These petrologically incompatible blocks were juxtaposed by post-metamorphic tectonic activity that was accompanied by the formation of brittle fault zones with elevated transmissibilities. The aim of this study was to define the spatial arrangement of these fault zones and their internal architecture by integrated evaluations of borecore and well-log data from a group of wells in the central part of the field. Spatial correlations between the reconstructed 1D lithologic columns revealed the main structural elements of the Szeghalom Dome. The low-angle (<15°) thrust faults most likely developed due to north-northwest vergent Cretaceous nappe tectonics, which was probably responsible for the juxtaposition of the different metamorphic blocks. A complex system of normal faults throughout the basement high provides evidence of intense Miocene extensional tectonic activity. This phase of the geodynamical evolution of the basin is believed to be responsible for the horst-graben structure of the Szeghalom Dome. The integration of the structural results with datasets of the paleo-fluid evolution, recent production and fracture network geometry indicates the importance of these fault zones in both the migration of hydrocarbons from the adjacent sub-basins to the overlying sediments and the development of significant storage capacity within the strongly fractured rock masses (mainly the amphibolite bodies). These observations of fluid flow also emphasized the impact of strong permeability anisotropy of the faults throughout the fractured reservoir.

Lithology identification using open-hole well-log data in the metamorphic Kiskunhalas-NE hydrocarbon reservoir, South Hungary

There are four main rock types along the ideal rock column of the Kiskunhalas-NE field; in order from the bottom upwards, orthogneiss, orthogneiss mylonite, graphitic gneiss mylonite and graphitic carbonate phyllite. These main rock types are characterized by significantly different reservoir features, as was proved by previous rock mechanical investigation. The geophysical information of well-logs (gamma, resistivity, neutron, density and acoustic logs) allows an understanding of the spatial extension of the good reservoir blocks. In the course of the examination conventionally applied plots, MN plots and discriminant function analysis were used. Three rock types were successfully identified along the wells, the graphitic carbonate phyllite, the mylonite and the orthogneiss. On the basis of the results, lithological boundaries could be estimated in numerous wells. These boundaries were presented along geological sections. Taking also the independent hydraulic regimes of the reservoir into account, a series of south-dipping normal fault-bounded blocks are assumed. Inside each block shallow-dipping mylonite/gneiss boundaries with a north-northeast dip direction are typical. The existence of this low-angled (less than 5°) mylonitized zone refers to a presence of a one-time detachment fault linked to the formation of a metamorphic core complex.

Statistical characterization of brittle and semi-brittle fault rocks: a clast geometry approach

In the present approach, clast geometric parameters—particle size distribution (PSD), clast complexity

New geothermal well-completion and rework technology by laser

(D^{R})

Quantification of soil organic matter degradation by Rock-Eval pyrolysis

(DR), aspect ratio (AR), circularity (Circ), convexity (Conv) and clast orientation (Angle)—were examined in order to separate the diverse fault rock types (fault breccias, cataclasites and fault gouges), which typically own extremely different hydraulic and petrophysical properties. The available borecore samples were studied in a case of a thrust fault zone from the metamorphic basement of the Pannonian Basin, Hungary. Multivariate statistical methods were applied in order to find the geometric parameters that define the tectonites. The calculated discriminant functions emphasized the importance of the PSD, Angle, AR, and Circ parameters, in descending order. We defined proper combinations of geometric parameters which can clearly separate the fault rock groups, both pair-wise and jointly for the three groups. The discriminant functions also pointed out the relatively similar geometric features of fault breccias and cataclasites in contrast to the significantly different characteristics of fault gouges. The multidimensional scaling demonstrated a three-phase evolution of the analysed brittle tectonites, where the initial deformation is coupled with chaotic fabric giving a weakly disaggregated fault breccia texture. The transitional stage can be characterised by cataclastic flow, while in the most deformed fault gouge samples the strong fragmentation, clast-rounding and oriented texture dominate. These results possible provide constraints on the development and overall behaviour of the fault zone.