Description
Converting zero or mixed phase wavelet into minimum phase
Phase conversion is very crucial step in Seismic data processing/imaging. If the phase of the data is not as client desired then we need to repeat the whole process from the beginning.
In Onshore and Offshore data acquisitions, we know the source. In the case of land we have Dynamite or Vibroseis as the source whereas Airgun is used as a source for Marine acquisition.
For Airgun and Dynamite the source will be in minimum phase. Vibroseis data is in Zero phase and we need to convert it to minimum phase.
Non symmetric, short duration and maximum energy (amplitude) at all frequencies are the characteristics of Minimum phase wavelet.
Deconvolution works best in minimum phase and it assumes that the data is in minimum phase. So either for land or marine, we should have a minimum phase wavelet prior to predictive deconvolution. For marine data, it will be helpful in attenuating the water reverberations.
In the case of Marine acquisition, source signature will be provided at the beginning of the survey and we call that as a far field source signature. If the far field signature is not provided then we can extract the source signature from the direct arrivals. Make sure not to confuse with the refracted energy. Take the far field source signature and add source/receiver ghost (if it doesn’t exist) and convolve them. Now we have to design a matching filter and make sure that the matching filter should be of the user objective. If you are working towards minimum phase conversion then the matching filter should be minimum phase only since the convolution of minimum phase wavelet and zero phase wavelet will result in a mixed phase.
Input data
Input DataItem
Input gather
Input model gather
Parameters
Conversion type
Choose the appropriate Conversion Type
We have Minimum Phase and Minimum Phase + Deconvolution.If you choose the Minimum Phase only, the source wavelet will be converted into Minimum phase only but no Deconvolution. In the latter case Deconvolution is performed which gives a better resolution and attenuates any ringing in the data.
Min Frequency
Provide the minimum frequency
Max Frequency
Provide the maximum frequency. It will vary based on the sample interval of the data. If the input data is 2ms then the maximum frequency will be 125 Hz which is the Nyquist frequency.
Prewhitening
Percentage Prewhitening noise added to the data
Smoothing spectrum window
Operanor window
Obsolete conversion
Here we have two options:
1.By all gather
2.By each trace