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A simplified analytical method useful for ductile ground support design in underground mine workings is presented. This approach allows for maintaining the stability of sidewalls in rectangular openings extracted in competent and homogeneous rocks, especially in high-pressure conditions, favoring rockburst event occurrence. The proposed design procedure involves the typical assumptions governing the limit equilibrium method (LEM) with respect to a triangular rock block expelled from a sidewall of a long mine excavation subjected to normal stresses of the values determined based on the Maugis's analytical solution concerned with stress distribution around the elliptical opening extracted within the homogeneous infinite elastic space. This stage of the local assessment of rock susceptibility to ejection from the walls of the excavation allowed for determining the geometry of the block whose ejection is most likely in a given geological and mining situation. Having extensive information about the geometry of the excavations and the properties of the surrounding rocks, it was possible to make an exemplary map of the risk from rockburst hazard, developed as the 2D contours of safety indexes' values, for special-purpose excavations such as heavy machinery chambers, main excavations, etc. in conditions of selected mining panel of the deep copper mine at Legnica-Głogów Copper Basin, Poland. Another important element of the obtained results is the calculated values of the horizontal forces potentially pushing out the predetermined rock blocks. These forces are the surplus over the potential of frictional resistance and cohesion on the surfaces of previously identified discontinuities or on new cracks appearing as a result of overloading of the sidewalls. Finally, the presented algorithm allows us to perform quantitative tracking of rockburst phenomena as a function of time by determination of acceleration, velocity, and displacement of expelled rocks. Such information may be useful at the stage of designing the support for underground workings. [ABSTRACT FROM AUTHOR]

A novel approach that couples hydrological and thermochronological modelling is tested in a well-known hydrothermal system, the Inner Western Carpathians, providing insights of the yet-unexplained Apatite Fission Track (AFT) ages of the Podhale Basin. Our new model improves previous ones by incorporating the effects of fluid circulation, by considering compaction, smectite dehydration and meteoric water as sources of fluid. Rock properties such as thermal diffusivity, porosity and permeability, are dependent on lithology and the effective-stress state of the system, making our calculations depart from previous efforts on thermochronological modelling. Particularly, we examined young (around 12 Ma) apatite fission track ages from Oligocene strata of the Podhale wild flysch, which suggest the occurrence of either substantial burial or an elevated basal thermal paleogradient, even though none of the above have been documented in the area. Such problem is addressed on this contribution, since by reproducing previous numerical experiments but adding groundwater circulation this time, improved thermally-reset AFT ages of the Podhale Basin are obtained. Thermal, hydrological and mineralogical observations are successfully reproduced, putting forward the calibration and validity of the model here proposed. Furthermore, our findings not only unveil the linking between the hydrological and thermal phenomena present in the study region, but also, trigger new questions on the processes that should be taken into account when thermochronological calculations are concerned. [ABSTRACT FROM AUTHOR]

Heterolithic complexes from the Carpathian Foredeep are a subject of growing attention as many natural gas accumulations of industrial importance have been discovered in such formations during the last decades. The aim of the presented work was to determine lithotypes of different lithology and mineralogical composition in the heterolithic sequences. Individual lithotypes were distinguished of macroscopic observations of cores, X-ray diffraction analysis (XRD) and X-ray fluorescence method (XRF). Preliminary distinction between the lithotypes was based on macroscopic observations of the core samples. Correlation plots between the contents of particular minerals (XRD analyses) and corresponding elements (XRF analyses) were used for verification of the lithotypes distinguished based on macroscopic observations. Swelling properties of the investigated rocks were determined using the cation exchange capacity (CEC) values. The following lithotypes were identified: medium-to fine-grained sandstones, fine- to very fine-grained sandstones, clayey sandstones, sand-dominated heteroliths, heteroliths with approx. equal proportions of sandstones and mudstones, mud-dominated heteroliths, mudstones, clayey shales. Such division provides a basis for precise petrophysical characterization of the analyzed profiles, that is assignment of particular petrophysical parameters values to individual lithotypes. More reliable petrophysical parameters in the geophysical interpretation of heterolithic sequences allow for a more precise determination of zones characterized by good reservoir parameters. [ABSTRACT FROM AUTHOR]

The research described in this article was carried out on samples of sandstone obtained from the underground excavations of four hard coal mines that operate in the region of Poland with the highest energy resources, i.e., Upper Silesia. The majority of underground tunnel excavations are mainly drilled using roadheaders, the organs of which are equipped with conical picks. The selection of pick type is usually based on rock compressive strength. However, sandstones often cause more problems during cutting compared to other waste rocks because of their variety. This article's primary purpose is to emphasize the importance of researching various properties of waste rock in addition to uniaxial compression strength, which is crucial in the selection of both the appropriate cutting method and appropriate cutting tools. Accordingly, relations between mineralogical, petrographic, physical and mechanical properties were examined in this study, with special attention paid to the abrasive properties that comprise rock abrasivity. Sandstones from the regions of Upper Silesia are characterized by a heterogeneity of mineralogical and petrographic features that strongly affect the physical and mechanical properties of these rocks, especially their abrasive properties. The determined correlations can aid understanding of the behavior of rocks during their mechanical cutting and facilitate the selection of appropriate cutting tools. [ABSTRACT FROM AUTHOR]

The purpose of seismic reservoir characterization is to predict the spatial distribution of the subsurface rock properties from a set of direct and indirect measurements. Commonly, rock property volumes are obtained in a two-steps approach. First, the elastic properties are inverted from seismic reflection data and then used to compute rock properties volumes by applying a calibrated rock physics models. Such an approach is not only time consuming but may also lead to biased results as the uncertainties related to seismic inversion may not be propagated through the entire geomodeling workflow. Here, we propose an iterative geostatistical shale rock physics seismic AVA inversion method to invert seismic reflection data directly for shale rock properties. The workflow consists of three main steps starting from shale properties model generation of brittleness, total organic carbon (TOC), and porosity using stochastic sequential simulation and cosimulation and calculation of a volume of shale. In the following step, elastic property volumes are calculated based on a calibrated shale rock physics model using the self-consistent approximation. The elastic models are then used for the calculation of the synthetic seismic data. In the final step, the misfit between synthetic and real data is calculated and used as part of the stochastic update of the model parameter space. The whole process is repeated until a minimum misfit between the observed and synthetic seismic is achieved. The proposed method is successfully tested on an onshore Lower Paleozoic shale gas reservoir in Northern Poland, and the predicted shale rock properties agree with those observed at a blind-well location. [ABSTRACT FROM AUTHOR]

The paper discusses the issue of oil-in-place estimation for liquid-saturated shales in Lower Paleozoic (Silurian and Ordovician) organic-rich formations of the Baltic Basin in North Poland. The authors adopted a geochemical method based on Rock Eval results which directly measure hydrocarbon content present in rock samples. Its application on a real data set required the implementation of correction procedures to consider also those oil compounds which were lost before Rock Eval measurements were taken or are not recorded in S 1 parameter. It was accomplished through the introduction of two correction coefficients: c 1 —for evaporation loss and c 2 —for heavier compounds underestimation. The first one was approximated on the basis of published results and known properties of crude oil, while the second one was addressed with laboratory experimental procedure which combines Rock Eval pyrolysis and rock sample extraction with organic solvents. The calculation formulas were implemented in the 3D geological model of shale formations reproducing their geometry as well as the spatial variability of the petrophysical and geochemical properties. Consequently, the results of oil-in-place estimation were also available as 3D models, ready for visualization and interpretation in terms of delineation of most favorable zones or well placement. The adopted geochemical method and the results of oil-in-place estimation it produced were confronted with standard volumetric method. Although both of them are volumetric methods, the results depend on different sets of rock properties, which is an advantage for result comparison reasons. The study revealed that the geochemical method of oil-in-place estimation in liquid-rich shales after appropriate adjustment, considering shale formation and reservoir fluid dependent conditions, could provide reliable results and be implemented on the early stage of shale exploration process in a condition of production data inaccessibility. [ABSTRACT FROM AUTHOR]

Permeability is a property of rocks which refers to the ability of fluids to flow through each substance. It depends on several factors as pore shape and diameter. Also the presence and type of clay has a large influence on the permeability value. Permeability can be measured on rock sample in the laboratory by injecting fluid through the rock under known condition, but this provides only point information. Due to the dependence of the parameter on many factors, the deterministic estimation of permeability based on laboratory measurement and well logs is problematic. Many empirical methods for determining permeability are available in the literature and interpretation systems. An interesting approach to the problem is the use of artificial neural networks based on laboratory measurement and modern, high-resolution logging tools. The authors decided to use MLP artificial neural networks, which allow permeability estimation and can be used both in the test well and applied to neighbouring wells. The network was checked in several variants. Obtained results show the legitimacy of using artificial neural networks in the issue of estimating permeability. However, they also show limitations resulting from the lack of accurate data or influence of geological setting and processes. [ABSTRACT FROM AUTHOR]

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Petrophysical evaluation of the Lower Permian formation was performed on the basis of the results of laboratory tests of rocks including pore space investigations using the Mercury Injection Capillary Pressure (MICP) method, the pore space saturation measurements by the Nuclear Magnetic Resonance (NMR) method, and measurements of the thermal conductivity coefficient by FOX series heat flow meters based on the one-dimensional Fourier equation. Three types of rocks: sandstones, conglomerates and effusive, sampled from the Ośno IG-2 well located in the Gorzów Block (NW part of Poland) were analysed. 42 core samples from the depth interval of 3212–3659 m bgl were tested. The results provide a wide range of information about the sample, primarily such parameters as pore size distribution, effective porosity and permeability, bulk density, sketal density, and thermal conductivity. The aim of the study was to determine the relevance of Lower Permian formation as a geothermal reservoir for CO 2 – EGS - Enhanced Geothermal Systems, which use carbon dioxide instead of water as working medium. Although worldwide research on such systems has been going on for many years, so far it has not been realized on a commercial scale. Moreover, to date there are no EGS installations in Poland. The ongoing research aims to bring the construction of the first pilot installation in Poland closer. Effusive rocks were characterized by lower value differentiation and relatively high lambda values (average 1.77–1.81 W/mK for dry samples, 2 W/mK for fully saturated and 2.1 W/mK for a mixture of water and CO 2), average effective porosity of 7.92% and permeability of 0.055 mD. Sandstones have the highest thermal conductivity values (1.87 W/mK at 20 °C, 1.87 W/mK at 50 °C, 1.82 W/mK at 100 °C and 1.79 W/mK at 150 °C), average effective porosity 5.56%, and permeability of 0.133 mD. For the conglomerates, the lowest values of thermal conductivity were obtained (average value for water-saturated sample equal 1.7 W/mK and for dry sample 1.4 W/mK). The average value of effective porosity for conglomerates is 7.66% and the permeability is 0.141 mD. The results indicate that the studied rocks have suitable parameters as a geothermal reservoir for CO 2 -EGS, especially effusive rocks. These parameters are similar to those of reservoir rocks for the EGS installation in Groß Schönebeck, as well as all types of rocks are classified primarily as petrothermal EGS. • Petrophysical parameters of the Lower Permian formation in the Gorzów Block are suitable for CO 2 -EGS. • Effusive rocks are characterized by the most suitable parameters as a geothermal reservoir for CO 2 -EGS. • Sandstones could also be potential reservoirs for CO 2 -EGS. • Conglomerates are characterized by the least suitable parameters as a geothermal reservoir for CO 2 -EGS. • The Lower Permian formation in the Gorzów Block has similar parameters to the Groß Schönebeck EGS reservoirs. [ABSTRACT FROM AUTHOR]

Mining-induced seismicity in the area of development works and proper mining operations is one of the major determinants of the rockburst hazard level in underground mines. Rockburst hazard assessment in Polish collieries is performed by a variety of mining and geophysical methods, including seismic and seismoacoustic techniques, borehole surveys, small diameter drilling, rock strata profiling and analyses of geomechanical properties of rocks, geological structure and geological mining conditions. In the case of zones particularly exposed to potential hazards, it is recommended that analytical or numerical forecasts of the state of stress in the vicinity of workings should be used already at the stage of planning of mining operations. This study summarises the comparative analysis of seismic test data and analytical forecasts of the state of stress in five selected headings in one of the burst-prone collieries within the Upper Silesia Coal Basin in Poland (USCB). As regards the seismic data, duly defined quantitative indicators and energy criteria of the registered seismic activity are recalled in the assessment of rockburst hazard level during the roadheading operations. Analytical simulations utilise a developed geomechanical model and stress–strain relationships stemming from the principles of elastic media mechanics. From the standpoint of mining engineering practice, interpretation of results obtained by the two methods reveals how effective analytical models will be in prognosticating or verification of rockburst hazard conditions. [ABSTRACT FROM AUTHOR]

Geomechanical characterization plays a key role in optimizing the stimulation treatment of tight reservoir formations. Petrophysical models help classify the reservoir rock as the conventional or unconventional type and determine hydrocarbon-saturated zones. Geomechanical and petrophysical models are fundamentally based on well-log data that provide reliable and high-resolution information, and are used to determine various relationships between measured borehole parameters and modeled physical rock properties in 3D space, with the support of seismic data. This paper presents the geomechanical characterization of the Middle Cambrian (Cm2) sediments from Eastern Pomerania, north Poland. To achieve the aim of this study, 1D well-log-based and 3D models based on seismic data of the rocks' petrophysical, elastic, and strength properties, as well as numerical methods, were used. The analysis of the Middle Cambrian deposits revealed vertical and horizontal heterogeneity in brittleness, the direction of horizontal stresses, and the fracturing pressure required to initiate hydraulic fractures. The most prone to fracturing is the gas-saturated tight sandstones belonging to the Paradoxides Paradoxissimus formation of Cm2, exhibiting the highest brittleness and highest fracturing pressure necessary to stimulate this unconventional reservoir formation. [ABSTRACT FROM AUTHOR]

Recognition of fractures and faults related to different types of folding is important for understanding how fluids flow in folds or which parts of folds represent a better productive sector of reservoirs due to, for example, changes in the intensity and distribution of fractures. In this paper, we suggest that seismic data alone may be insufficient to determine the style of buckle folding. The differences in mechanical properties of the rock masses favour the development of two main types of internal deformation within the buckle folds, that originated as a result of layer-parallel shortening: flexural slip/flow folding and neutral-surface folding. However, it is difficult to tell from seismic data alone which type of deformation had occurred. This paper presents the advantages of analyzing structures in core combined with results of amplitude variation with azimuth (AVAZ) analysis applied on the 3D seismic survey, when compared to the use of seismic data alone. To illustrate this, we use examples of seismic-scale folds, interpreted as buckle folds formed within the Pomeranian segment of the Caledonian Foredeep Basin. The analysis of structures related to the amplification of one fold known as the Opalino Anticline leads us to conclude, that this approach allowed us to recognize that folding within the mostly homogenous, isotropic Ordovician and Silurian mudstone formations is associated with bed-parallel and bed-perpendicular veins, reverse faults, thrusts, stylolites and normal faults, which formed at different depths within the fold. We consider the structures to have developed as a result of buckling of the mudstone formations and demonstrate that the process facilitated neutral-surface folding, which caused outer-arc extension in the higher parts of the Opalino Anticline and the development of an inner-arc contraction zone in the lower parts of the anticline. We show that this approach helps to predict the distribution of structures related with folding, which in turn aids in estimating the reservoir quality. • Seismic data alone may be insufficient to determine the style of buckle folding. • Structures observed in cores, compared with seismic data and supported by the results of the AVAZ technique allow to interpret the style of folding in buckled rocks. • The strain pattern during layer-parallel shortening within the Pomeranian segment of the Caledonian Foredeep Basin was controlled by the mechanical properties of mostly homogenous, isotropic Ordovician-Silurian mudstones. • The layer-parallel shortening of the relatively homogenous, isotropic rock sequence facilitated neutral-surface folding. • Upper Silurian (Pridoli) growth strata demonstrate that folding in this part of the Caledonian Foredeep Basin occurred during the Pridoli. [ABSTRACT FROM AUTHOR]

This paper presents a broad overview of laboratory methods for measuring thermal properties and petrophysical parameters of carbonate rocks, and analytical methods for interpreting the obtained data. The investigation was conducted on carbonate rock samples from the Kraków region of Poland in the context of shallow geothermal potential assessment. The measurement techniques used included standard macroscopic examinations; petrophysical investigations (porosity, density); analysis of mineral composition thermal conductivity (TC) and specific heat measurements; and advanced investigations with the use of computed tomography (CT). Various mathematical models, such as layer model, geometric mean, and spherical and non-spherical inclusion models, were applied to calculate thermal conductivity based on mineralogy and porosity. The aim of this paper was to indicate the optimal set of laboratory measurements of carbonate rock samples ensuring sufficient characterization of petrophysical and thermal rock properties. This concerns both the parameters directly characterizing the geothermal potential (thermal conductivity) and other petrophysical parameters, e.g., porosity and mineral composition. Determining the quantitative relationship between these parameters can be of key importance in the case of a shortage of archival thermal conductivity data, which, unlike other petrophysical measurements, are not commonly collected. The results clearly show that the best correlations between calculated and measured TC values exist for the subgroup of samples of porosity higher than 4%. TC evaluation based on porosity and mineral composition correlation models gives satisfactory results compared with direct TC measurements. The methods and results can be used to update the existing 3D parametric models and geothermal potential maps, and for the preliminary assessment of geothermal potential in the surrounding area. [ABSTRACT FROM AUTHOR]

Underground coal exploitation often results in land-surface subsidence, the rate of which depends on geological characteristics, the mechanical properties of the rocks, and the applied extraction technology. Since mining-related subsidence is characterized by "fast" displacement and high nonlinearity, monitoring this process by using Interferometric Synthetic Aperture Radar (InSAR) is very challenging. The Small BAseline Subset (SBAS) approach needs to predefine an a priori deformation model to properly estimate an interferometric component related to displacements. As a consequence, there is a lack of distributed scatterers (DS) when the selected a priori deformation model deviates from the real deformation. The conventional differential SAR interferometry (DInSAR) approach does not have this limitation, since it does not need any deformation model. However, the accuracy of this technique is limited by factors related to spatial and temporal decorrelation, signal delays due to the atmospheric artifacts, and orbital or topographic errors. Therefore, this study presents the integration of DInSAR and SBAS techniques in order to leverage the advantages and overcome the disadvantages of both methods and to retrieve the complete deformation pattern over the investigated study area. The obtained results were evaluated internally and externally with leveling data. Results indicated that the Kriging-based integration method of DInSAR and SBAS can be effectively applied to monitor mining-related subsidence. The root-mean-square Error (RMSE) between modeled and measured deformation by InSAR was found to be 11 and 13 mm for vertical and horizontal displacements, respectively. Moreover, DInSAR technique as a cost-effective and complementary method to conventional geodetic techniques can be applied for effective monitoring fast mining subsidence. The minimum and maximum RMSE between DInSAR displacement and specific leveling profiles were found to be 0.9 and 3.2 cm, respectively. Since the SBAS processing failed in subsidence estimation in the area of maximum deformation rate, the deformation estimates outside the maximum rate could only be compared. In these areas, the good agreement between SBAS and DInSAR indicates that the SBAS technique could be reliable for monitoring the residual subsidence that surrounds the subsidence trough. Using the proposed approach, we detected subsidence of up to −1 m and planar displacements (east–west) of up to 0.24 m. [ABSTRACT FROM AUTHOR]

Paleoclimatic effects may still influence the present day subsurface temperature distribution and therefore the heat flow density calculated in affected depth levels. Cooling of several degrees Celsius into depths of up to 1.5 – 2 km were reported for areas which were strongly affected by the Pleistocene ice ages (e.g. Canada, Poland, and Denmark). However, although this phenomenon is well known, not much research has been performed to quantify these processes in Northern Germany, an area where Pleistocene ice margins of the last ice ages are located. To fill that gap we compiled new data from two boreholes in the eastern part of the North German Basin, one located beneath the former ice shield of the last glaciation, and one located in the foreland. We determined thermal rock properties (thermal conductivity, thermal diffusivity, and specific heat capacity) on drill core samples and used it as calibrator for well-log based calculations of thermal parameter profiles along the borehole. The results were used for heat-flow computations with depth and implemented as a base for an analytical solution of the heat equation as well as inversion modelling. By showing the discrepancy of observed and theoretical background temperature and heat flow density profiles, we aim to improve the understanding of the regional thermal response to the last glaciations. [ABSTRACT FROM AUTHOR]