Geology Reference
In-Depth Information
Ricker
20Hz
Ormsby
5-10-35-60 Hz
Butterworth
18dB/Oct 12Hz -
12dB/Oct40Hz
Zero Phase
Minimum Phase
0
twt
Amplitude spectra
1
1
1
1
Amp
Amp
Amp
Amp
0
0
0
0
0
75
0
75
0
75
0
75
Hz
Hz
Hz
Hz
Figure 3.10
Examples of idealised wavelets.
but the Ricker wavelet is often a useful tool for first-
pass synthetics, given its simplicity.
to be evaluated, for example with well ties (
Chapter 4
).
It is essential that this process does not boost noise
levels in the data. In the worst case scenario the
apparent improvements suggested by the high-
frequency look to the data may not be real. When
correctly applied the amplitude corrections give rise
to data that have true relative amplitude and the phase
correction enhances vertical resolution, particularly
Amplitude and phase corrections can be applied indi-
vidually or in combination.
3.6 Wavelet phase and processing
In order to enhance the interpretability of seismic a
number of processes can be applied to the data. Typ-
ically these relate to the zero phasing of the seismic,
compensation for absorption effects and bandwidth
improvement. These are not mutually exclusive and
the processor/interpreter needs to evaluate appropri-
ate approaches for the data at hand.
3.6.2 Zero phasing
The process of zero phasing seismic is conceptually
straightforward. If the wavelet is known (for example
from wavelet extractions (
Chapter 4
)) then a convo-
lution operator can be applied to transform it to zero
phase (
Fig. 3.12
). In practice, this process is not
always carried out in this way owing to uncertainties
in the definition of the wavelet. One problem is that
different wavelet extraction methods can give different
3.6.1
Q
compensation
correcting for the exponential loss of high-frequency
energy and increasing wavelet distortion with increas-
ing two-way time.
Figure 3.11
shows an example
where this type of amplitude and phase compensation
has been applied. In this case the result is fairly
dramatic but the usefulness of the correction needs
29
