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Szegedi H.,University of Miskolc | Dobroka M.,University of Miskolc | Somogyi Molnar J.,MTA ME Research Group of Geoengineering
Near Surface Geoscience 2014 - 20th European Meeting of Environmental and Engineering Geophysics | Year: 2014

The Fourier-transform (FT) often results noisy Fourier spectrum because this operation is linear and contaminate noise in time domain dataset appear in the frequency domain also. Especially, in case of non- Gaussian nature of the noise distribution (for example outliers in the data sets) can cause appreciable distortions in the Fourier spectra. If we treat the FT as an over-determined inverse problem, the noise effect on the Fourier spectrum can be greatly reduced. The geophysical series inversion was used for the discretization. The scaled Hermite functions - note that they are eigen-functions of the FT - were chosen as basis function. During the inversion process by using the Steiner-weights we get a highly robust inversional FT method. Numerical tests show the significant noise rejection capability of the new inversion based FT algorithm. Source


Molnar J.S.,MTA ME Research Group of Geoengineering | Kiss A.,University of Miskolc | Dobroka M.,University of Miskolc
76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 | Year: 2014

Acoustic velocity in rocks is strongly depends on pressure, indicating that wave propagation is very nonlinear and the quasistatic elastic properties of rocks are hysteretic. Characterization of hysteretic behavior is important for a mechanical understanding of reservoirs during depletion. Therefore a quantitative model -which provides the physical explanation -of the mechanism of pressure dependence is required. In this paper a petrophysical model is presented which describes the connection between the propagation velocity of acoustic wave and rock pressure both in case of pressurization and depressurization cycles as well as explains the mechanism of acoustic hysteresis. The developed model is based on the idea that the pores in rocks close during pressurization and reopen during depressurization. It is valid also for S wave velocities since the basis of the model is the change of pore volume. The model was applied to acoustic P and S wave velocity data sets. The parameters of the petrophysical model were determined by a linearized inversion method. The calculated data matched accurately with measured data proving that the new rock physical model describing acoustic hysteresis applies well in practice. Source


Somogyi Molnar J.,MTA ME Research Group of Geoengineering | Kiss A.,University of Miskolc | Dobroka M.,University of Miskolc
76th European Association of Geoscientists and Engineers Conference and Exhibition 2014: Experience the Energy - Incorporating SPE EUROPEC 2014 | Year: 2014

Pressure strongly influences the mechanical, transport and elastic properties of rocks, such as acoustic velocity, porosity and elastic moduli. Seismic and borehole logging techniques measure these rock properties in order to infer subsurface information. To relate changes in seismic attributes to reservoir conditions, a thorough understanding of pressure effects on rock properties is essential. Therefore it is important to develop a petrophysical model based on simple physical assumptions which describes the relationship between Lamé constants as well as acoustic velocities and pressure. In this paper we present a rock physical model based on the idea that the pore volume of a rock is decreasing with increasing pressure to describe the pressure dependence of P and S wave velocities thereby the Lamé constants. Laboratory measured acoustic P and S wave velocities as a function of pressure -published in literature -are inverted to prove the applicability of the model and to obtain that of parameters. The quality checked joint inversion results showed that the calculated data matched accurately with measured data and also proved that the suggested petrophysical model performs well in practice. Source


Somogyine Molnar J.,University of Miskolc | Somogyine Molnar J.,MTA ME Research Group of Geoengineering | Kiss A.,University of Miskolc | Dobroka M.,University of Miskolc | Dobroka M.,MTA ME Research Group of Geoengineering
Acta Geodaetica et Geophysica | Year: 2015

Understanding the relationship between pressure and rock physical parameters, such as acoustic velocities, elastic moduli, porosity is essential for exploring and exploiting of natural reserves. In this study we introduce petrophysical models which describe the relationship between acoustic P, S wave velocities as well as quality factors and pressure. The models are based on the idea that the pore volume of a rock is decreasing with increasing pressure. On the basis of the models the pressure dependent Lamé coefficients and loss angles were deduced. Laboratory measured acoustic P and S wave velocities and quality factors as a function of pressure were inverted to prove the applicability of the models and to obtain that of parameters. The quality checked joint inversion results showed that the calculated and measured data matched accurately and also proved that the suggested petrophysical models perform well in practice. © 2014, Akadémiai Kiadó. Source


Kovacs F.,MTA ME Research Group of Geoengineering | Turai E.,MTA ME Research Group of Geoengineering
Idojaras | Year: 2015

The cycle properties of the annual average, absolute maximum, and absolute minimum precipitation values have been calculated from precipitation data the Matra and Bukk regions. The cycle parameters of annual average and annual absolute maximum precipitation values have been determined using the data of a shorter 34-year (19702006) and a longer 53-year (1960-2012) period (38 precipitation measurement stations) through the determination of the parameters of frequency, amplitude, and phase with an analytic version of the discrete Fourier transform (DFT), and the values obtained on the basis of the two periods have been compared. Using prognosis parameters, a prognosis until 2025 has been made. Then, the regression function of the variation in time of average and absolute maximum precipitation values has been determined on the basis of actual and prognosticated data for the whole period (1960-2025). © 2015, Hungarian Meteorological Service. All rights reserved. Source

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