|Publisher||Offshore Technology Conference||Language||English|
|Content Type||Conference Paper|
|Title||IMPROVEMENT OF MARINE SEISMIC DATA AS A RESULT OF SOURCE SIGNATURE STUDIES|
|Authors||Thomas R. Shugart and Joe D. Matthews, Teledyne Exploration|
Offshore Technology Conference, 8-11 May , Houston, Texas
|Copyright||1978. Offshore Technology Conference|
A typical marine signature results from the combination of source signature, source and receiver ghosts, receiver array response, and recording instrument response. In the time domain, these elements are combined by convolution to form the signature. In the frequency domain, they are combined by multiplication of their amplitude spectra and addition of their phase spectra. These components are Illustrated individually in both domains.
Each of the component elements of the signature Is band limited in some way and thus degrades the resolution of the data. Some of these elements may also degrade the depth of penetration of the data by limiting its low frequency content. Certain data acquisition parameters should therefore be carefully tailored to suit the objectives of the survey.
When the signatures associated with seismic data sets are known, it is possible in processing to use this knowledge to enhance the resolution of the data. It is advantageous to attempt this improvement in two separate steps. First, the phase spectrum of the seismic wavelet may be reduced to zero with an appropriate all-pass filter. In the second step, an attempt is made to broaden the amplitude spectrum. This step is usually more difficult. Due to the limitations inherent in the acquisition of the data, there is an unavoidable trade off between resolution and signal-to-noise ratio. Thus, efforts to broaden the spectrum tend to degrade this ratio, In spite of this limitation, careful spectral balancing can produce remarkable results. These effects are displayed with illustrations from real data.
In true first part of this paper we will describe a typical marine seismic wavelet, showing how it may be synthesized from field measurements. We will then explore ways in which this knowledge of the wavelet can be exploited to improve resolution in seismic data, both in the acquisition and processing phases. Finally, we will show an example of real data illustrating these improvements.
The term "signature" as used in this paper will refer to the shape of the acoustic pulse radiated by the seismic source as modified by source and receiver ghosts, receiver array, and recording instruments. Specifically excluded from this definition are reverberations, multiples or any periodicities associated with the water bottom or subsurface layering. By the term "ghost" we mean the reflection of an upgoing wave at the sea-air surface. "Near-field" will mean less than one wavelength distant from the source. "Far-field" will mean many wavelengths distant.
A TYPICAL MARINE SIGNATURE
In Figure 1 we see a typical marine signature or wavelet. The energy source was an array of 6 airguns consisting of 3 airguns of 300 cu.in. size and 3 air guns of 540 cu.in. size. Two airguns of each size were equipped with bubble suppression devices and one airgun of each size was without the bubble suppressor. The airguns were pressurized to 2000 psi.
|File Size||483 KB||7|