Geology Reference
In-Depth Information
Near
Far
NI reflection
series
Estimated
wavelet
Full stack
trace
Synthetic
Seismic
trace
Residuals
-100
-100
0
-50
-50
2000
0
0
TWT
ms
50
50
150
150
2300
Amplitude
Amplitude
Figure 4.30
Initial well tie: full stack and zero offset synthetic
(after Simm et al.,
1999
).
Figure 4.29
Wavelets showing different scaling extracted from
near and far seismic cubes.
but it is still a good idea to check the scaling manually
as gross differences between actual seismic and well-
based expectations may be a pointer to problems in the
seismic processing sequence.
NI reflection
series
Estimated
wavelet
Full stack
trace
Synthetic
Seismic
trace
Residuals
0
4.6.6 Use of matching techniques to
measure an improving tie
Historically, it was common practice to tie migrated
full stack seismic sections to zero offset synthetics,
usually because only a full stack dataset was available
and a shear velocity log had not been acquired. It is
generally accepted now that the reflectivity series
used in well matching should be calculated at the
effective angle of the stack (
Chapter 2
).
Figure 4.30
shows an example (from Simm et al.,
1999
)wherean
initial tie was made to full stack data using a zero
offset reflectivity series, although the top reservoir is
characterised by Class IIp reflectivity. The tie is not a
good one: PEP
2000
TWT
ms
2300
Figure 4.31
Improved well tie: intercept stack and zero offset
synthetic calculated from invasion-corrected logs (after Simm et al.,
1999
). Note the arrow marks the top reservoir on the synthetic.
phase error is 9°), and the top reservoir is now
clearly tied from synthetic to seismic.
It is evident from this discussion that well ties are
a critical part of seismic interpretation and that ana-
lytical approaches give valuable information to the
interpreter. They also provide a useful tool in guiding
seismic processing (Barley,
1985
).
¼
43% and estimated phase error
is 16°. The top reservoir is not clearly identified on
the full-stack seismic. Subsequent re-processing of
the seismic to create an intercept (i.e. zero offset)
stack and log conditioning to remove the effects of
fluid invasion resulted in the tie shown in
Fig. 4.31
.
The tie is improved (PEP
¼
72% and estimated
57
