SALIM JABEEDROLL NO-4APGD IN PETROLEUM EXPLORATION GEOPHYSICS DEPARTMENT OF APPLIED GEOLOGYDIBRUGARH UNIVERSITY

PRESENTED BY

VIBROSEIS DECONVOLUTION

MECHANISM

WHY USE V IBROSEIS METHOD? L I N K S \ U S E O F V B . p p t x

PROBLEMS

• EMBEDDED WAVELET

• MIXED PHASE WAVELET

CROSS CORRELATION OF SWEEP

TRACE

EMBEDDED SWEEP

KLAUDER WAVELET WAVELETLINKS\klauder.pptx

BASICS OF DECONVOLUTIONLINKS\conv.ppt

LEAVES AREFLECTION COEFFICIENT WHEREEVER A CHANGE IN ACOUSTIC IMPEDANCE

TEMPORAL RESOLUTION

TWO ASSUMPTIONS ARE NECESSARY FOR DECONVOLUTION

1. WAVEFORM DOESNOT CHANGES ITS SHAPE

2. MINIMUM PHASELINKS\ZERO PHASE.pptx

METHODS OF MINIMUM PHASE DECONVOLUTION METHODS

FREQUENCY DOMAIN DECONVOLUTION

• FREQUENCY-DOMAIN SWEEP DECONVOLUTION (FDSD) UTILIZES THE CONCEPT THAT CONVOLUTION IN THE TIME-DOMAIN IS EQUIVALENT TO

MULTIPLICATION IN THE FREQUENCY DOMAIN.

•DECONVOLUTION OF THE SWEEP IN THE TIME DOMAIN CAN BE COMPLETED IN THE FREQUENCY DOMAIN THROUGH DIVISION.

THE BASIC CONVOLUTION EQUATION FOR A VIBROSEIS SOURCE ISx(t) = s(t) * r(t)

WHERE X(T) IS THE TRACE RECORDED BY THE GEOPHONE, S(T) IS THE SOURCE SWEEP AND R(T) IS THE REFLECTIVITY.

FOR FDSD IT IS EASIER TO EXPRESS THE BASIC CONVOLUTION EQUATION FOR A VIBROSEIS SOURCE IN THE FREQUENCY-DOMAIN AS

x (ω ) = s(ω )r(ω ). THE SWEEP CAN THEN BE REMOVED IN THE FREQUENCY-DOMAIN BY DIVIDING THE TRACE BY THE SWEEP,

S(ω), giving a solution of:

If the sweep input into the ground is equal to the sweep generated then the result is the exact reflectivity.

MIXED PHASE WAVELET

ZONE NEAR THE SHOT

REFLECTIVITY SEQUENCE OF WAVES

NEAR SURFACE WAVES

EARTH ATTENUATION

The earth filtering e(t), is included in the basic convolution equation for avibroseis source as,

x(t) = r(t) * e(t) * s(t).

In the frequency-domain the convolutional equation is defined as,

X (ω ) = R(ω )E(ω )S(ω ).

THE RESULT IS THE REFLECTIVITY CONVOLVED WITH THE MINIMUM-PHASE WAVELET THAT IS CREATED BY THE EARTH-ATTENUATION

MINIMUM-PHASE DECONVOLUTION SHOULD BE ABLE TO COMPLETELY REMOVE THE MINIMUM-PHASE WAVELET FROM THE DATA

METHODS HAVE BEEN DESIGNED TO REMOVE THE MIXED-PHASE WAVELET THAT IS CREATED THROUGH THE INITIAL VIBROSEIS PROCESSING

A KLAUDER WAVELET FROM THE PROCESSING OFVIBROSEIS SOURCE DATA

CONVERTING THE MIXED-PHASE WAVELET TO ZERO-PHASE BY CONSTRUCTING A MINIMUM-PHASE EQUIVALENT OF THE KLAUDER WAVELET AND FILTERING THE VIBROSEIS RECORD TO MATCH THE PHASE

A MINIMUM-PHASE WAVELET

ONCE THIS IS COMPLETED, IT IS POSSIBLE TO USE MINIMUM-PHASE SPIKING DECONVOLUTION TO REMOVE THE MINIMUM-PHASE WAVELET, CREATING A ZERO-PHASE RECORD

generated wavelet recorded in vibroseis acquisition.

CONCLUSIONS

FREQUENCY-DOMAIN SWEEP DECONVOLUTION USES THE FREQUENCY-DOMAIN TO REPLACE DECONVOLUTION WITH DIVISION.

THIS ELIMINATES THE EMBEDDED KLAUDER WAVELET THAT REMAINS IN THE DATA WHEN CROSSCORRELATION IS UTILIZED.

THIS ASSISTS IN REMOVING THE PROBLEM OF THE MIXED-PHASE WAVELET ASSOCIATED WITH THE KLAUDER WAVELET AND THE MINIMUM-PHASE EARTH FILTER.

THANK YOU