Geology, Geophysics & Environment
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ISSN 2299-8004
e-ISSN: 2353-0790
Issue Date
2020
Volume
Vol. 46
Number
No 2
Description
Journal Volume
Geology, Geophysics & Environment
Vol. 46 (2020)
Projects
Pages
Articles
Determination of stress state based on well logging data and laboratory easurements - a CBM well in the southeastern part of the Upper Silesian Coal Basin (Poland)
(Wydawnictwa AGH, 2020) Kępiński, Michał
The main objective of this study is to present calculation methods of horizontal stress profiles, taking into account the stress boundaries model, poro-elastic horizontal strain model and the effective stress ratio approach, using calibration with wellbore failure. The mechanical earth model (MEM) parameters from log measurements and well testing data were estimated for a well located in the southeastern part of the Upper Silesian Coal Basin. Log-derived horizontal stresses of the well are commonly treated as the final product of geomechanical modeling in oil and gas practices. A less popular method for estimating horizontal stresses is based on Kirsch equations juxtaposed with compressional and tensile failure observed on a micro-imager or six-arm caliper. Using this approach, horizontal stresses are determined based on the fact that when hoop stresses exceed the formation’s tensile strength, tensile fractures are created, and when those stresses exceed the compressive strength of the formation, breakouts can be identified. The advantage of this method is that it can be run without in situ stress measurements. The presented workflow is recommended every time there is an image log and dipole sonic measurement in the available dataset, both being necessary to observe the failure zones and MEM.
An evaluation of the impact of shot and receiver lines spacing on seismic data quality - the Wierzbica 3D AGH seismic experiment
(Wydawnictwa AGH, 2020) Barmuta, Jan Paweł; Korbecka, Monika; Hadro, Piotr; Pieniądz, Krzysztof; Stefaniuk, Michał; Dzwinel, Krzysztof; Buniak, Arkadiusz
An attempt was made to describe the quality of the stacked seismic data semi-quantitatively with respect to the spacing of shot and receiver lines. The methods used included: signal-to-noise ratio calculation, seismic-to-well tie accuracy, wavelet extraction effectiveness and reliability of semi-automated interpretation of seismic attributes. This study was focused on the Ordovician-Silurian interval of the Lublin Basin, Poland, as it was considered as a main target for the exploration of unconventional hydrocarbon deposits. Our results reconfirm the obvious dependency between the density of the acquisition parameters and data quality. However, we also discovered that the seismic data quality is less affected by the shot line spacing than by comparable receiver line spacing. We attributed this issue to the fact of the higher irregularity of the shot points than receiver points, imposed by the terrain accessibility. We have also proven that the regularity of receiver and shot point distribution is crucial for the reliable interpretation of structural seismic attributes, since these were found to be highly sensitive to the acquisition geometry.
Last scene in the large scale rotations of the Western Carpathians as reflected in paleomagnetic constraints
(Wydawnictwa AGH, 2020) Márton, Emö
This paper provides an overview of the paleomagnetic results which constrain the post-Paleogene tectonic development of the Western Carpathians. A group of these results are relevant to the last stage of the Tertiary folding and thrusting of the Silesian, Dukla and Magura nappes of the Outer Western Carpathian and were obtained from Paleogene-Lower Miocene flysch sediments. Both the pre- and post-folding remanences indicate about 50° CCW vertical axis rotation with respect to the present orientation. This is about a 60° rotation relative to stable Europe. It follows that the general orientation of the Silesian and more internal nappes were NW-SE, at least until the mid-Miocene. The CCW vertical axis rotation was coordinated with that of the Central Carpathian Paleogene Basin. The termination of the rotation can be estimated from the paleomagnetic data available from the Pieniny andesites which intruded the Pieniny Klippen Belt and the southern part of the Magura Nappe as well as from those obtained for the Neogene intramontane basins which opened up in the Outer and in the Central Western Carpathians. The paleomagnetic vectors for the andesites form two groups. The first group suggests about 45° CCW rotation relative to north, while the second shows no rotation. At the present stage of our knowledge it seems likely that some of the andesite bodies were intruded around 18 Ma, which is the oldest isotope age for the intrusions of the Wżar Mts, while some other bodies could have been emplaced after the rotation, around 11 Ma, which is the youngest isotope age for the Brijarka quarry. Vertical axis CCW rotation was also observed on sediments older than 11.6 Ma in the Orava-Nowy Targ Intramontane Basin which saddles the Magura Nappe and the Central Carpathian Paleogene Basin. However, this rotation was related to fault zone activity and was not attributed to the general rotation of the Outer Western Carpathian nappe system. Paleomagnetic results from the Nowy Sącz Intramontane Basin, which opened over the Magura Nappe, and those for the Central Western Carpathian Turiec Intramontane Basin do not indicate vertical axis rotation. In the first case, the loosely controlled age limit of the termination of the rotation is around 12 Ma. Well constrained results from the second basin imply that the rotation was definitely over by 8 Ma. Based on the above observations, and aware of the problem of often loose age control on the formation and deformation of the deposits of the intramontane basins, it is tentatively concluded that the large scale CCW rotation of the Central Western Carpathians, together with the Magura, Dukla and Silesian nappes, must have started after 18 Ma and terminated around 11 Ma.
Land satellite imagery and integrated geophysical investigations of highway pavement instability in southwestern Nigeria
(Wydawnictwa AGH, 2020) Ademila, Omowumi; Olayinka, Abel Idowu; Oladunjoye, Michael Adeyinka
The high global numbers of road accidents due to bad roads and the failure of other engineering structures have necessitated this study, particularly as road transport accounts for a higher percentage of cargo movement in African countries. The geophysical investigation was carried out on six failed and two stable sections along the Ibadan-Iwo-Osogbo highway to examine the geological factors responsible for highway failure in the area. A Landsat ETM+ (Enhanced Thematic Mapper Plus) imagery of the study area and its environs was acquired and processed for lineaments analyses. Magnetic, Very Low Frequency Electromagnetic (VLF-EM) and electrical resistivity methods involving Schlumberger Vertical Electrical Sounding (VES) and 2-D imaging using a dipole-dipole array were utilized. Lineaments were identified across failed localities. Lateral magnetic variations in the near-surface geological materials characterized the study area. The 2-D VLF-EM models generated showed conductive zones corresponding to fractured zones of conductive clay materials within the basement rocks. Subgrade soils below the highway pavement along the failed sections are typical of incompetent clayey and sandy clay/clayey sand formations with resistivity values between 20–475 $\Omega \cdot$ m. In comparison, the subgrade soil beneath the stable sections has moderate to high resistivity values of 196–616 $\Omega \cdot$ m. 2-D resistivity structures across the failed segments identified low resistivity water-absorbing clay and lithological contacts. Water absorbing, clay enriched subgrade soils and the identified near-surface linear conductive features are the major geologic factors, and poor drainage network resulted in the highway failure. Remote sensing and geophysical investigations of the geological sequence and structures underlying the highway should be carried out before construction to effectively complement the routine geotechnical studies to ensure the sustainability of road infrastructure.
Changes in the methane emissions and hard coal output in the Brzeszcze mine (the Upper Silesian Coal Basin, Poland)
(Wydawnictwa AGH, 2020) Dreger, Marcin
The paper presents the variability of methane emissions in mining excavations in the Brzeszcze mine (Poland) against the background of hard coal output, geological and mining factors. The geological structure of the Upper Silesian Coal Basin (USCB) is very diverse. The Brzeszcze coal deposit is located close to the large and permeable Jawiszowice fault which increases the methane hazard during mining activities performed close to this fault. The overall decrease in hard coal output (1988–2018) has coincided with a rapid increase in methane emissions (1997–2018). Throughout the study period, hard coal output decreased threefold from 3.9 to 1.2 million Mg annually. Coal extraction in high methane content beds (e.g. 510, 405/1, 364, 352) increases the total methane ($CH_{4}$) emission into mining excavations, aggravating the methane hazard due to the high explosiveness of the gas. To protect miners, coal workings need to be continuously ventilated, taking the harmful gas out of the mine (ventilation air methane emission) or methane needs to be captured by underground methane systems (degassing). Every year, over 34 million m$^{3}$ of $CH_{4}$ is captured by the drainage systems and over 70 million m$^{3}$ $CH_{4}$ (average) is discharged through ventilation shafts into the atmosphere. The presence of the large, permeable regional dislocation, the Jawiszowice fault zone, shaped the methane concentration in the fault vicinity, when the highest methane emissions during coal mining was studied.