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Abstract

Volcanic successions of the Kecel Basalt Formation (KBF) occur in the southern part of the Pannonian Basin. As a result of periodic submarine eruptions, the basaltic and pyroclastic rock horizons were intercalated with layers of the Late Miocene Endrod Marl Formation, which is regarded as one of the most important hydrocarbon source rocks in the area. The KBF was discovered through almost 30 wells between 2,200 and 2,900 meters of depth. Due to the high fracture porosity, some parts of the formation show good reservoir characteristics and act as important migration pathways of hydrocarbon-bearing fluids. Since the reservoir is presumably fracture-controlled, this study concentrates on the evolution of fractures crosscutting the rock body. Based on textural and mineralogical features, four distinct vein types can be distinguished, of which the first three types are discussed in this paper. Beside calcite, quartz, feldspar, and chlorite, the veins are cemented by various zeolite minerals. The vertical dimension of the dominant zeolite zone indicates the burial-diagenetic type of zeolite zonation and suggests subsidence of the subaqueous basalt after formation.

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In this study, new microthermometric data of fluid inclusions distributed along planar assemblages crosscutting a metamorphic quartz lens from the Mecsekalja Zone metamorphic complex are presented. Three fluid generations are defined, none of which have previously been identified by earlier paleofluid evaluations of the study area. Petrographic description of the host quartz is provided to identify textures related to crystalloplastic deformation resulting from ductile deformation. The textural relationship of the studied assemblages to the dynamic recrystallization features is discussed. The possible affinities of the fluids introduced in this study to those identified in the region by previous authors are discussed. The affinities and timing of the fluid flow events are discussed based on the physicochemical properties of the fluids. One local carbonic (high XCO2) fluid is recognized. A high- and a moderate-salinity fluid generation are also revealed. The relationship of these fluid generations to those defined in earlier studies from the Mórágy Granite and the Baksa metamorphic complex contributes new knowledge to the recognition of the regional paleofluid evolution.

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Fractured fluid reservoirs are of key importance for recovering water and hydrocarbon supplies and geothermal energy, or in predicting the subsurface flow of pollutants. There are several fractured metamorphic-basement HC reservoirs in the Pannonian Basin; one of the largest among them is the Szeghalom Dome in SE Hungary. Previous production and fluid inclusion data infer that in this case several unconnected fluid regimes must coexist in the basement, making modeling of the fracture network essential. Because the representative volume of a fractured rock mass is usually too large to measure hydraulic properties directly, stochastic calculations should be carried out, which are consistent with observed deformation history and stochastic patterns. Input statistical data (orientation, length, distribution, fractal dimension for fracture seeds) were determined for amphibolite and gneiss samples representing the Szeghalom Dome. Data were measured simultaneously using binocular microscope and computerized X-ray tomography. Comparison of the two data sets suggests that they are comparable and both can be used for modeling. A new computer program, called REPSIM has been developed recently, which follows a fractal geometry-based discrete fracture network (DFN) algorithm to simulate the fracture network. The evaluation of simulated networks suggests that amphibolite and gneiss-dominated parts of the basement behave differently; large amphibolite bodies have a connected fracture network, while gneiss domains usually are well below the percolation threshold.

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Central European Geology
Authors: Péter Bajcsi, Tamás Bozsó, Róbert Bozsó, Gábor Molnár, Viktor Tábor, Imre Czinkota, Tivadar M. Tóth, Balázs Kovács, Félix Schubert, Gábor Bozsó and János Szanyi

Our research team has developed a new well completion and rework technology involving lasers. The system is made up of a high-power laser generator and a custom-designed directional laser drilling head. The laser head is attached to a coiled tubing unit to maximize production and to carry out special downhole tasks. In this phase of the development effort, laser technology is particularly well suited to cost-efficiently drill short laterals from existing wells in a single work phase, drilling through the casing and cement as well as the formation. The technology, which is an extended perforation solution, enables a more intensive interaction with the downhole environment and supports cutting edge subsurface engineering scenarios such as barite removal. Laser-induced heat treatment appears to be a suitable alternative to effectively remove the almost immovable deposits and scales from thermal water-well pipes.

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