VẬT lý địa CHẤN 12 freq

Overview Fundamentals Introduction Seismic waves: Propagation Velocity and Amplitudes Seismogram Measurement systems Sources, receivers, Acquisition strategies Data processing “Pre-processing” Filter und Deconvolution Velocity analysis and Stacking Migration Interpretation Basic scheme of the seismic data processing Loading of the data/conversion Demultiplexing Geometry Measurements Navigation Pre-Processing Editing Amplitude correction Frequency filter Deconvolution CMP-Sorting Prestack Velocity analysis NMO-Correction Stacking Migration Poststack Post-processing Printing/storage Printing/storage Frequency analysis • Analysis of the frequency content of the data • Difference in frequency content for interface waves, Noise and Reflections • In what frequency range are the reflections present ? Outline • Periodic and transient waveforms • Fourier transformation time domain frequency domain • Frequency filters • Tapering • Field examples Frequency content of a shot high freq noise: low freq ground-roll Waves Amplitude Phase φ Acos(2πft) Acos(2πft-φ) t Period τ == f Period τ Wavelength λ=τ∗v 2π Wavenumber k = λ Velocity v = f⋅λ 2π -ω Periodic and transient waveforms Periodic waveform Transient waveform Periodic waveforms • Any periodic waveform, may be decomposed into a series of sine (or cosine) waves whose frequencies are integer multiples of the basic repetition frequency • It is necessary to define not only the frequency of each component, but also its amplitude and phase Fourier transformation Fourier Transformation: ∞ G( f ) = −i πft ( ) g t e dt ∫ −∞ G( f ) = ∞ ∞ −∞ −∞ ∫ g (t )cos(2πft )dt − i ∫ g (t )sin(2πft )dt ∞ Inverse Fourier Transformation: g (t ) = ∫ G ( f )e i 2πft df −∞ ∞ ∞ −∞ −∞ g (t ) = ∫ G ( f ) cos(2πft )df + i ∫ G ( f )sin( 2πft )df Summation of different frequencies Fourier transformation g(t) A(f) Amplitude-Spectrum φ(f) Phase-Spectrum G(f) = A(f) e iφ(f) where A(f)={[Real part of G(f)]2+[Imaginary part of G(f)]2}1/2 Φ (f)=tan-1 ( imaginary part of G(f) real part of G(f)] ) A(f) Imaginary part Φ (f) Real part • frequency • amplitude • phase f1 f2 Sum: f1 f2 Sum: f1 f1 f2 f2 Sum: Sum: Digital representation of continuous amplitude and phase spectrum associated with a transient waveform Spike function DC bias Transient waveforms approximating seismic pulses Frequency filter Low Pass High Pass f f Notch filter Band Pass f f Tapering Tapering of filters • Butterworth • Hanning • Ormsby Amplitude and phase characteristics Band-pass filtered raw field records Corrected for geometric spreading: frequency absorption remains [...]... imaginary part of G(f) real part of G(f)] ) A(f) Imaginary part Φ (f) Real part • frequency • amplitude • phase f1 f2 Sum: f1 f2 Sum: f1 f1 f2 f2 Sum: Sum: Digital representation of continuous amplitude and phase spectrum associated with a transient waveform Spike function DC bias Transient waveforms approximating seismic pulses Frequency filter Low Pass High Pass f f Notch filter Band Pass f f Tapering... f Notch filter Band Pass f f Tapering Tapering of filters • Butterworth • Hanning • Ormsby Amplitude and phase characteristics Band-pass filtered raw field records Corrected for geometric spreading: frequency absorption remains ... Fourier transformation time domain frequency domain • Frequency filters • Tapering • Field examples Frequency content of a shot high freq noise: low freq ground-roll Waves Amplitude Phase... Frequency analysis • Analysis of the frequency content of the data • Difference in frequency content for interface waves, Noise and Reflections • In what frequency range are the reflections present... a series of sine (or cosine) waves whose frequencies are integer multiples of the basic repetition frequency • It is necessary to define not only the frequency of each component, but also its