SELECTION OF TEST PARAMETERS FOR IDENTIFYING NONLINEAR DYNAMICS OF TIME SERIES WHEN ANALYZING SEISMIC BACKGROUND RECORDS OVER A HYDROCARBON DEPOSIT
Oil and Gas Research Institute, Russian Academy of Sciences
Journal: Geophysical research
Tome: 25
Number: 4
Year: 2024
Pages: 37-62
UDK: 550.3;51-37
DOI: 10.21455/gr2024.4-2
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Chebotareva I.Ya. SELECTION OF TEST PARAMETERS FOR IDENTIFYING NONLINEAR DYNAMICS OF TIME SERIES WHEN ANALYZING SEISMIC BACKGROUND RECORDS OVER A HYDROCARBON DEPOSIT
// . 2024. Т. 25. № 4. С. 37-62. DOI: 10.21455/gr2024.4-2
@article{ChebotarevaSELECTION2024,
author = "Chebotareva, I. Ya.",
title = "SELECTION OF TEST PARAMETERS FOR IDENTIFYING NONLINEAR DYNAMICS OF TIME SERIES WHEN ANALYZING SEISMIC BACKGROUND RECORDS OVER A HYDROCARBON DEPOSIT
",
journal = "Geophysical research",
year = 2024,
volume = "25",
number = "4",
pages = "37-62",
doi = "10.21455/gr2024.4-2",
language = "English"
}
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Keywords: seismic background, bicoherence, surrogate series, oil, gas, thermodynamic indicator, nonlinearity.
Аnnotation: Our recent studies using the dissipative seismic method have revealed a linear dependence between the total thickness of productive intervals at a hydrocarbon deposit and the value of the thermodynamic indicator of the degree of non-equilibrium state of rocks. Moreover, the linear dependence was formed only in a limited frequency range from 1 to 6 Hz and was destroyed when the frequency range was expanded towards increasing values. It is reasonable to assume that all these features are associated with the fact that a hydrocarbon deposit is a nonlinear filter that effectively interacts with the seismic background and generates a signal at the difference frequency of propagating harmonics with close frequencies. There are methods for direct testing of this hypothesis, allowing to identify the nonlinearity of time series and to detect frequencies with nonlinearly coupled phases in the wave field in case of their presence.
This article presents the results of the first stage of the study – recognition of nonlinear dynamics of the seismic background over a hydrocarbon deposit. Numerical modeling was used to refine the parameters for the selected test for Gaussianity and linearity, and to demonstrate the test reliability on model time series, Gaussian and non-Gaussian, with stochastic, linear, and nonlinear dynamics. In testing field records it is showen that the dynamics of the natural seismic background over the oil deposit is significantly non-Gaussian and nonlinear. The bicoherence surface, a two-dimensional function of frequencies, has a complex oscillating shape for real data. The lines of maxima and minima satisfy the condition f 1 + f 2 = const. At frequencies of 1–10 Hz, the bicoherence values increase with decreasing frequencies. At frequencies above 20 Hz, the bicoherence surface reaches a value that coincides with the value of the mean shift for a stochastic Gaussian process. Since the seismic background process is essentially non-Gaussian, the model of the additive sum of Gaussian noise and the useful signal in the form of harmonics cannot be used in detection of phase-coupled triplets. Also, known theoretical estimates obtained for Gaussian processes cannot be used to determine the significance level. The significance level should be estimated separately for each set of field data, for example, using the surrogate series method, choosing a method that allows adequately describing essentially nonlinear series. All the obtained results can be directly used to analyze geophysical series of various physical nature.