NOISE ATTENUATION USING RADON FILTER
ORIGINAL/RN SPECTRA COMPARISON
Radon filter is very efficient but has two concerns
· It can eliminate signal in case of using excessive severe parameters
· Only acts on gathers
A method applicable to stacked or non-stacked data is proposed.
GATHERS RESAMPLING FROM 4 TO 1 MS (non-mandatory process)
1st DERIVATIVE CALCULATION ON RESAMPLED GATHERS
Maximums and minimums (peaks and througs) of a continuous function (seismic trace) become null values (crosses at 0) when applying the derivative to such function.
Script: Locates the zero crossings in the derived trace and replaces them with the coincident seismic amplitude generating spike series (The replacement points are mathematically simple to locate since their amplitude coordinate is 0)
SPIKE SPECTRUM (THEORETICAL)
A series of (theoretical) spikes must be associated with an infinite frequency. Since this cannot be achieved, the series obtained is limited by the new sampling interval (1 ms) that defines a half period (half wavelength) with this value.
COMPARISON: GATHERS DERIVATIVE / GATHERS SPIKE
COMPARISON: GATHERS DERIVATIVE / GATHERS SPIKE (DETAIL)
COMPARISON ORIGINAL GATHER / FILTERED GATHER SPIKE (Low cut: 10 Low pass: 20 High pass: 80 High cut: 120)
COMPARISON ORIGINAL GATHER / FILTERED GATHER SPIKE (DETAIL)
SPECTRUM COMPARISON: ORIGINAL / ENHANCED FREQUENCY
The frequency content of the final product shows an increase in the frequency content in the range of higher values (from 60 Hz onwards). The decay in the lower range is a consequence of the low-cut filter applied (Low cut: 10 Low pass: 20)
COMPARISON: PSTM MIGRATION / STACK FILTERED SPIKE GATHERS
COMPARISON: PSTM MIGRATION / STACK FILTERED SPIKE GATHERS (DETAIL)
SYNTHETIC SEISMOGRAM BY SPIKE CONVOLUTION WITH PHASE 0 WAVELET AND FREQUENCY 80 HZ
Convolution of a spike (reflection coefficient) with a phase 0 wavelet generates a trace in the same phase.
COMPARISON OF SYNTHETIC SEISMOGRAM IN PHASE 0 AND MINIMUM PHASE
COMPARISON: STACK CRP GATHERS / STACK GATHERS SPIKE CONVOLUTED WITH PH0 WAVELET 80 Hz
COMPARISON: STACK GATHERS SPIKE CONVOLUTED WITH PH 0 WAVELETS : 80 Hz / 120 Hz
CONCLUSIONS
· Both solutions (filter application or convolution) achieve a frequency content higher than the original.
· They can be applied on gathers as well as on stacks, whether migrated or not.
· The convolution solution ensures the final phase (0) and facilitates procedures involving wavelet extraction (synthetic seismogram, trace inversion, etc.).
· It provides greater certainty for interpretation as it facilitates the assignment of geological events to their seismic equivalents.
· Do not discard starting the task flow with a soft radon filter (only valid for pre stack data).
Bibliography High-Frequency Enhancement of Seismic Data by Reconvolution Kevin Gerlitz
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