Tivadar M. Tóth | University of Szeged (original) (raw)

Papers by Tivadar M. Tóth

74th EAGE Conference and Exhibition incorporating EUROPEC 2012, Jun 4, 2012

In this paper the workflow covering the geological modelling of a Hungarian natural fractured fie... more In this paper the workflow covering the geological modelling of a Hungarian natural fractured field is presented. The objective of this workflow is to define the 3D grid properties which best describe fractures and further to transform and export them in a suitable format for running a dual porosity simulation in Eclipse or any simulator. To model the fracture distribution and to identify and include in the geological model those limited number of individual pathways that define the fluid transport, the discrete fracture network (DFN) approach was applied. In the 3D model the reservoir fracture network was represented by planar surfaces, considering fracture geometric and hydraulic properties. The novelty of our approach is twofold; firstly it is about the integration of different scale measurements for fracture characterisation, secondly we have calibrated the DFN by changing the conductivity of the fractures until a good match was found between the calculated permeability and the permeability calculated from k*H. From the geological point of view, we can conclude that two main fracture sets, characterised by a mean strike /dip of 299.6/56.4 and 165.1/63.6. can be identified. The open fracture network orientation is consistent with the main stress direction identified from borehole breakouts.

Cereal Research Communications, 2008

$Research paper thumbnail of Palaeofluid evolution in a fractured basalt hosted reservoir in the Üllés-Ruzsa-Bordány area, southern sector of the Pannonian Basin$

Geologia Croatica, Nov 23, 2016

Extensive Miocene volcanic activity produced basaltic and pyroclastic successions, which were pen... more Extensive Miocene volcanic activity produced basaltic and pyroclastic successions, which were penetrated by many wells in the area of Üllés-Ruzsa-Bordány, in the western and central part of the Great Hungarian Plain. The Kecel Basalt comprises primary porosity from a high proportion of vesicles and significant secondary fracture porosity, as well. Due to the significant fracture porosity, some depth intervals show good reservoir characteristics, although the fractures crosscutting the rock body are partly or entirely cemented by various minerals. Based on the textural and mineralogical features, four distinct vein types can be distinguished, named after their volumetrically most abundant cement phases, i.e. potassium-feldspar (Kfp-), calcite (Cal-), laumontite (Lmt-) and analcime (Anl-) types. This study focuses on probably the youngest of these vein types, the Anl-type. Based on the study of veins and mineral sequences, the direction of temperature changes cannot be given unequivocally for every stage of cementation, but crystallization of the Anl-type veins might have occurred at lower temperatures than the formation of the Lmt-type veins. Fluid inclusion studies suggest that hydrocarbon migration and accumulation took place after cementation of the first three vein types (Kfp-, Cal-and Lmt-types). In the newly opened fracture system, two types of hydrocarbon (HC1 and HC2)-bearing fluid inclusion assemblages were captured during precipitation of analcime and later zeolites. This refers to two stages of hydrocarbon migration in the fracture system. Observations of the fluorescence colours and low temperature behaviours of the hydrocarbon-bearing inclusions, the earlier HC1 petroleum-inclusions captured heavier (presumably less mature oils), while the later ones (HC2) lighter (presumably more mature) oils. The HC2 petroleum seems to be very similar to the crude oil sampled in a well in the area based on their fluorescence parameters.

Central European Geology, Mar 1, 2017

$Research paper thumbnail of Using geophysical log data to predict the fracture density in a claystone host rock for storing high-level nuclear waste$

Acta geodaetica et geophysica, Mar 1, 2023

Previously drilled boreholes of a host rock for a potential nuclear waste repository in Hungary r... more Previously drilled boreholes of a host rock for a potential nuclear waste repository in Hungary revealed a highly fractured claystone rock body. A crucial step for characterizing the hydrodynamic behavior of such a fractured reservoir is fracture identification and accurate calculation of the fracture density. Although acoustic borehole televiewers provide a reliable base for determining the fracture density, older boreholes usually lack such data. However, conventional borehole geophysical measurements are often accessible in such cases. The aim of this study was to identify any correlations between well log data and fracture density. Multiple linear regression analysis was performed on data from two boreholes penetrating the Boda Claystone Formation in southwest Hungary. The upper section of the BAF-4 borehole was used for training, where the fracture density was estimated with a fit of R 2 = 0.767. The computed regression function predicted the fracture density with high accuracy in both boreholes for all intervals with typical lithological features. However, in some sections where anomalous well log data indicated changes in the lithology, the prediction accuracy decreased. For example, the function underestimated the fracture density in sandy intervals. Article highlights • Fracture density of a potential nuclear waste repository predicted by using regression analysis on geophysical logs. • Fracture density of a claystone body influenced by resistivity and density. • Prediction accuracy may be influenced by grain size, bedding type, and presence of reductive layers.

Geologia Croatica, Nov 1, 2015

The basement of the Pannonian Basin contains several fractured metamorphic hydrocarbon reservoirs... more 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 Békés 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 higher transmissibilities. The aim of this study was to define the spatial arrangement of these fault zones and their internal architecture by integrated evaluations of borehole core 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 were 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 geodynamic 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 palaeo-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 anisotropic permeability anisotropy of the faults throughout the fractured reservoir.

Applied sciences, Feb 28, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Journal of Analytical and Applied Pyrolysis, Aug 1, 2005

This paper presents an application of Rock-Eval pyrolysis for estimating the proportion of the co... more This paper presents an application of Rock-Eval pyrolysis for estimating the proportion of the components with different thermal stability in soil organic matter, the maturity of which corresponds to the early stage of diagenesis. For testing the validity of the modified Rock-Eval method, parallel series of pyrolysis were carried out on sedimentary rock samples. The temperature program was selected on the basis of the results obtained from stepwise Rock-Eval pyrolyses and from the mathematical deconvolution of pyrograms. The proportion of the original biomolecules in soil organic matter was calculated by the integration of pyrograms below 350°C and could be determined rapidly by one single pyrolysis using 350°C as initial cracking temperature. At 380°C, both the mathematical and the experimental methods provide reliable information about the proportion of the humic substances. Conversely, for rock samples, mathematical deconvolution of the pyrograms showed the heterogeneity of the sedimentary organic matter, the maturity of which corresponds to late diagenesis, without any estimation of the proportion of the different components. The rate of organic carbon accumulation in the studied soils and the decomposition rate of biopolymers were interpreted as a function of land-use and redox conditions. Differences in the precursor vegetation and in the environmental parameters resulted in markedly reduced carbon storage and higher degree of humification in the agricultural soil than in the adjacent forest soil. Redox conditions strongly affected both the amount and the elemental composition of the stored organic matter. The decomposition rate of biopolymers appeared to be controlled mainly by the contribution of resistant lignin components to the source biomass and, to a lesser extent, by redox conditions.

$Research paper thumbnail of Hydrothermal palaeofluid circulation in the fracture network of the Baksa Gneiss Complex of SW Pannonian Basin, Hungary$

Geofluids, Mar 17, 2011

A well-developed fracture-filling network is filled by dominantly Ca-Al-silicate minerals that ca... more A well-developed fracture-filling network is filled by dominantly Ca-Al-silicate minerals that can be found in the polymetamorphic rock body of the Baksa Gneiss Complex (SW Hungary). Detailed investigation of this vein network revealed a characteristic diopside fi epidote fi sphalerite fi albite ± kfeldspar fi chlorite1 ± prehnite ± adularia fi chlorite2 fi chlorite3 fi pyrite fi calcite1 fi calcite2 fi calcite3 fracture-filling mineral succession. Thermobarometric calculations (two feldspar: 230-336°C; chlorites: approximately 130-300°C) indicate low-temperature vein formation conditions. The relative succession of chlorites in the mineral sequence combined with the calculated formation temperatures reveals a cooling trend during precipitation of the different chlorite phases (T chlorite1 : 260 ± 32°C fi T chlorite2 : 222 ± 20°C fi T chlorite3 : 154 ± 13°C). This cooling trend can be supported by the microthermometry data of primary fluid inclusions in diopside (T h : 276-362°C) and epidote (T h : 181-359°C) phases. The identical chemical character (0.2-1.5 eq. wt% NaCl) of these inclusions mean that vein mineralization occurred in a same fluid environment. The high trace element content (e.g. As, Cu, Zn, Mn) and Co ⁄ Ni ratio approximately 1-5 of pyrite grains support the postmagmatic hydrothermal origin of the veins. The vein microstructure and identical fluid composition indicate that vein mineralization occurred in an interconnected fracture system where crystals grew in fluid filled cracks. Vein system formed at approximately <200 MPa pressure conditions during cooling from approximately 480°C to around 150°C. The rather different fluid characteristics (T h : 75-124°C; 17.5-22.6 eq. wt% CaCl 2) of primary inclusions of calcite1 combining with the special d 18 O signature of fluid from which this mineral phase precipitated refer to hydrological connection between the crystalline basement and the sedimentary cover.

Central European Geology, Mar 1, 2016

The pre-Cenozoic basement of central Hungary is partly made up of different types of carbonate ro... more The pre-Cenozoic basement of central Hungary is partly made up of different types of carbonate rocks. These carbonates are often good hydrocarbon reservoirs, and hydrocarbon production is significant in this region in Hungary. Nonetheless, the petrography of the reservoir rocks has not yet been investigated in detail. In this study, the results of the investigations of the lithology of a carbonate hydrocarbon reservoir from central Hungary (Gomba Field) are presented. Based on this work, two types of pure limestone, a dolomitic limestone and a polymictic breccia, could be distinguished in the study area. The limestone types are similar to the Kisfennsík Limestone Member and the Berva Limestone of the Bükk Mountains, but they contain significant amounts of framboidal pyrite and dead oil as vein fillings. The breccia is predominantly composed of angular carbonate clasts and minor metamorphic and sedimentary rock fragments in a chaotic pattern. The breccia has some grains that may be speleothems (e.g., stalactite or stalagmite) based on their structure and isotopic compositions. The fabric of the breccia suggests that it may have been formed by fluidrelated processes. Cross-cutting relationships of the veins and petrography of the vein fillings suggest that there are four different fracture generations and two different hydrocarbon migration phases to be distinguished. The composition of the hydrocarbon-bearing fluid inclusions related to the second migration event is similar to the crude oil currently produced from the Gomba Field. During the Eocene, the Triassic basement was buried and brecciated. Subsequently, a primary hydrocarbon migration can be assumed, but the hydrocarbons became overmature, apparently due to the high temperatures of the burial environment. Finally, an uplift phase began and the youngest fracture generation formed, which serves as a primary pathway for the more recent hydrocarbon migration.

$Research paper thumbnail of Discrete fracture network (DFN) modelling of a high-level radioactive waste repository host rock and the effects on its hydrogeological behaviour$

Journal of Structural Geology, Mar 1, 2022

Applied sciences, Sep 4, 2019

Red mud usually contains a significant amount of rare elements. Exact knowledge about their accum... more Red mud usually contains a significant amount of rare elements. Exact knowledge about their accumulation tendencies as well as identification of those minerals, which store these elements, would help planning better extraction technologies.

$Research paper thumbnail of Structural reconstruction of a fractured fluid reservoir using single quartz grains of drilling chips$

Journal of Petroleum Science and Engineering, Dec 1, 2020

During their operation, modern aircraft engine components are subjected to increasingly demanding... more During their operation, modern aircraft engine components are subjected to increasingly demanding operating conditions, especially the high pressure turbine (HPT) blades. Such conditions cause these parts to undergo different types of time-dependent degradation, one of which is creep. A model using the finite element method (FEM) was developed, in order to be able to predict the creep behaviour of HPT blades. Flight data records (FDR) for a specific aircraft, provided by a commercial aviation company, were used to obtain thermal and mechanical data for three different flight cycles. In order to create the 3D model needed for the FEM analysis, a HPT blade scrap was scanned, and its chemical composition and material properties were obtained. The data that was gathered was fed into the FEM model and different simulations were run, first with a simplified 3D rectangular block shape, in order to better establish the model, and then with the real 3D mesh obtained from the blade scrap. The overall expected behaviour in terms of displacement was observed, in particular at the trailing edge of the blade. Therefore such a model can be useful in the goal of predicting turbine blade life, given a set of FDR data.

ABSTRACT Fractured Variscan crystalline rocks store a significant amount of hydrocarbon throughou... more ABSTRACT Fractured Variscan crystalline rocks store a significant amount of hydrocarbon throughout the basement of the Pannonian Basin. Using a detailed analysis of metamorphic rocks and microtextures, a complex PTd history were assembled for the Dorozsma reservoir (SE Pannonian Basin). On this basis crystalline blocks of different evolution were defined, which also show differences in fracture network geometry and fluid migration capacity. The results are in good agreement with seismic data and help better understanding the behaviour of the reservoir.

Open Geosciences, 2016

Multilateral wells have been increasingly used in recent years by different industries including ... more Multilateral wells have been increasingly used in recent years by different industries including oil-and gas industry along with coal bed methane-and water production. The common purpose of these wells is to achieve a higher production rate per well. More and more sophisticated well patterns and geometries can be implemented in practice which calls for improved modelling techniques. Complicated well geometries and small lateral diameters require high resolution models in the vicinity of the wells. With structured finite difference grids this can only be achieved by unnecessary refinements even far away from the wellbores. However the model may still suffer from orientation problems if laterals do not coincide with the rows or columns of the rectangular mesh. In the present work, we applied unstructured grids to model multilateral wells and compared the results to structured models. We used the MODFLOW-USG code, which simulates groundwater flow using a generalized control volume finite-difference approach, allowing grids other than orthogonal structured grids to be applied. This offers a solution for orientation and resolution problems. The second part of the paper aims to optimize multilateral well geometry by evaluating the effect of length, angle and number of laterals.