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1

Dynamic elastic properties of the hard coal seam at a depth of around 1260 m

Krawiec Krzysztof

Gospodarka Surowcami Mineralnymi

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2021

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T. 37, z. 3

159--176

EN

The knowledge of the dynamic elastic properties of a coal seam is important in the context of various types of calculations of the seam behavior under various stress-strain conditions. These properties are often used in numerical and analytical modeling related to maintaining the stability of excavations and the analysis of mechanisms, e.g. related to the risk of rock bursts. Additionally, during the implementation of seismic surveys, e.g. seismic profiling and seismic tomography in coal seams, the reference values of the elastic properties of coal are used in the calculation of relative stresses in various geological and mining conditions. The study aims to calculate the dynamic elastic parameters of the coal seam located at a depth of 1,260 m in one of the hard coal mines in the Upper Silesian Coal Basin (USCB). Basic measurements of the velocity of P- and S-waves were conducted using the seismic profiling method. These surveys are unique due to the lack of the velocity wave values in the coal seam at such a great depth in the USBC and difficult measurement conditions in a coal mine. As a result, dynamic modulus of elasticity was calculated, such as Young’s modulus, volumetric strain modulus, shear modulus and Poisson’s ratio. The volumetric density of coal used for calculations was determined on the basis of laboratory tests on samples taken in the area of the study. The research results showed that the calculated mean P-wave velocity of 2,356 m/s for the depth of 1,260 m is approximately consistent with the empirical relationship obtained by an earlier study. The P-wave velocity can be taken as the reference velocity at a depth of approx. 1,260 m in the calculation of the seismic anomaly in the seismic profiling method.

PL

Znajomość dynamicznych właściwości sprężystych pokładu węgla jest istotna w kontekście różnego rodzaju obliczeń zachowania się pokładu w różnorakich warunkach naprężeniowo-odkształceniowych. Właściwości te są często wykorzystywane w modelowaniach numerycznych i analitycznych związanych z utrzymaniem stateczności wyrobisk oraz analizą mechanizmów, np. związanych z zagrożeniem tąpaniami. Dodatkowo w trakcie realizacji badań sejsmicznych np. profilowań sejsmicznych i tomografii sejsmicznej w pokładach węgla referencyjne wartości właściwości sprężyste węgla wykorzystywane są w obliczaniach naprężeń względnych w różnych warunkach geologiczno-górniczych. Celem badań jest obliczenie dynamicznych sprężystych parametrów pokładu węgla, położonego na głębokości około 1260 m, w jednej z kopalń węgla kamiennego w Górnośląskim Zagłębiu Węglowym. Podstawowe pomiary prędkości fal sejsmicznych wykonano metodą profilowania sejsmicznego. Te pomiary są unikatowe ze względu na dużą głębokość położenia profilu pomiarowego oraz trudne warunki pomiarowe w kopalni. W efekcie obliczono dynamiczne moduły sprężystości takie jak: moduł Younga, moduł odkształcenia objętościowego, moduł odkształcenia postaciowego oraz współczynnik Poissona. Gęstość objętościową węgla przyjętą do obliczeń wyznaczono na podstawie testów laboratoryjnych na próbach pobranych w rejonie badań. Wyniki badań pokazały, że obliczona średnia prędkość fali P równa 2356 m/s dla głębokości 1260 m jest w przybliżeniu zgodna z empirycznymi zależnościami określonymi we wcześniejszych badaniach. Prędkość fali P może być przyjęta jako prędkość odniesienia na głębokości około 1260 m w obliczeniach anomalii sejsmicznej w metodzie profilowania sejsmicznego.

2

Brittleness index analysis of coal samples

Wu Haibo, Zhang Pingsong, Dong Shouhua, Huang Yaping, Zhang Min

Acta Geophysica

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2019

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Vol. 67, no. 3

789--797

EN

The brittleness index (BI), which serves as a key reference for reservoir fracturing, is also an important quantitative index for the evaluation of coal-bed methane (CBM) reservoirs. To address the lack of research regarding this application of the BI, we measured the ultrasonic wave velocity of 10 coal samples collected from the Qinshui Basin, China. We then calculated the BI in three test directions, i.e., BI(90°), BI(45°), and BI(0°), as well as the BI anisotropy value (ABI) using the dynamic elastic method. Analysis of the calculated results showed that BI(90°) generally had the highest values and that BI(45°) was close to BI(0°). The ABI showed a positive correlation with the dynamic Young’s modulus anisotropy value, dynamic Poisson’s ratio anisotropy value, S-wave velocity anisotropy value, and the ratio of P-wave and S-wave velocity anisotropy values. However, the ABI had an unclear correlation with the P-wave velocity anisotropy value. Further analysis of the correlation between the BI and two other reservoir parameters (coal structure type and fracture development) revealed that samples with high BI values generally corresponded to primary or fragmented types of coal and also had low Poisson’s ratios, which indicates undeveloped fractures, while samples with low BI values corresponded to granulated types of coal and had high Poisson’s ratios, which indicates developed fractures. We investigated these correlations in order to understand the multiparameter constraints and their combined application in brittleness evaluations, which could reduce risk and improve the precision of ideal brittleness identification in CBM reservoirs.

3

Measurements and interpretation of well logs in the Jeziórko sulphur deposit, Tarnobrzeg, Poland

Jarzyna J., Bała M.

Geological Quarterly

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2000

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Vol. 44, Nr 2

157-166

EN

Geophysical logs of borehole F-380 drilled through the Jeziórko sulphur deposit near Tarnobrzeg are interpreted in terms of mineral composition and porosity. Measurements were made from a standard set of logs by Geokar Geophysical Co. and from using university prototype logging equipment developed for shallow boreholes. Comparative analysis was made of GR and gamma ray spectroscopry, density, neutron-gamma, epithermal neutron, and acoustic logs. The interpretation yielded values for the volume of limestone, clay mineral content, sulphur content, and porosity while the barite content in the sulphur deposit was determined from a four-log set (GR, neutron-gamma, density, and acoustic). A gamma ray log with the uranium window subtracted, GRS, used instead of GR, gave the distinct drop of shaliness and caused the distinct changes of sulphur content for selected intervals of the section examined. To test the geophysical interpretation, the sulphur content of core samples of limestone was determined by three different techniques: ICP-AES analysis, sample combustion in the LECO automatic analyser and X-ray phase analysis. Clay mineral identification in the overburden was attempted using the Th vs. K cross-plot. Acoustic full wavetrains were used for rapid identification of formation zones with different elastic parameters. The dynamic coefficient of rock elasticity, i.e. the Poisson coefficient, was obtained from P-wave and S-wave velocities, determined in situ from acoustic full wavetrains.