Method for surveying oil and gas based on Morlet spectrum

Abstract

The utility model relates to a method for surveying oil and gas based on a Morlet spectrum, which comprises the steps as follows: firstly, Fourier analysis is implemented on seismic signals in a target reservoir of a seismic recording channel to obtain the frequency spectrum scope of the seismic signals; secondly, the seismic signals are analyzed by using continuous wavelet transform to obtain wavelet transform coefficient Wx (b, s); thirdly, the instantaneous amplitudes under different scale factors s are defined as follows: the instantaneous amplitude values [Ai(b0,1 / ai)i is equal to 0, 1,..., N] corresponding with different scale factors ai is obtained for each time point b0; Lagrange splines are used for implementing interpolation; the amplitude values of any frequence at a b point can be obtained through the substituting of the corresponding a value; in the way, a connecting line of the discrete points forms the frequency spectrum of the b point, namely the Morlet spectrum; and fourthly, the absorption coefficients of each point are obtained according to the instantaneous amplitudes at any time point obtained in step 3); if the absorption coefficient Xi I of the point is lower than the absorption coefficient of a wall rock by more than ten percent, then the position is represented to comprise an air layer.

Description

technical field [0001] The invention relates to the field of energy exploration and development, in particular to a method for surveying oil and gas based on Morlet spectrum. Background technique [0002] In the process of oil and gas seismic exploration, when the seismic wave propagates in the viscoelastic medium, the elastic energy of the seismic wave is gradually absorbed by the medium and converted into thermal energy. The process of converting elastic energy into thermal energy is called absorption. Gas-bearing strata can cause strong absorption of high-frequency seismic wave energy, and its attenuation coefficient can be used to detect the presence or absence of oil and gas. [0003] The traditional calculation of absorption coefficient is to use the window Fourier transform to obtain the amplitude spectrum, and use the high-frequency amplitude-spectrum ratio to calculate the high-frequency attenuation of seismic signals, that is, the absorption coefficient. Using the...

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Problems solved by technology

Using the tool of Fourier analysis, although the attenuation phenomenon of high-frequency energy can be observed, it is difficult to describe the detailed changes of energy

If you want to calculate the absorption coefficient of a certain point, you generally need to calculate the Fourier transform of a time window centered on this point first, but the calculation of attenuation based on the time window Fourier transform has the following problems: if the time window is too large, the calculated The frequency spectrum has an average effect in the time window, and the time locality of the frequency spectrum is very poor, which affects the accuracy of the absorption coefficient, and it is difficult to accurately describe the position of the sand layer attenuated by high frequencies, that is, the obtained results cannot meet the time locality of seismic records Requirements; On the contrary, if the time window is too small, or expect to have a higher time resolution, the nature of the Fourier transform will produce serious boundary effects, that is, the Gibbs effect, the obtained spectrum is affected by the boundary Pollution, there will be many false images, affecting the accuracy of the absorption coefficient, and it cannot reflect the real situation of the seismic signal well

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