Exploration Insights November 2019 | Page 34

Receivers
Source
Location of all possible
solutions for source–receiver
arrangements
CMP
Sweep Ellipse
b)
Figure 4> Image showing the construction of a synthetic seismogram from the Volve Field.
These coefficients are then substituted by wavelets proportional
to this coefficient (Figure 4) that can then be compared with the
seismogram.
1
2
TWT
Ties between well and seismic data allow chronostratigraphic and
depositional models to be populated into the seismic data, along with
a calibration of models for rock properties. This level of integration is
vital for revealing the true lithological and petrophysical properties of
the subsurface.
Unmigrated data
c)
Amplitudes are located at CMP
1
1´
2´
2
Seismic interpretation is carried out in software packages that allow
the identification of faults and the lateral tracking of continuous
reflectors (Figure 1). A number of derived products are made from
these interpretations that include structure maps and/or the isopach
between them (figures 1B and C). Rock or fluid properties are also
calculated by applying algorithms to the seismic data (e.g. AVO
interpretation).
Stage
γ-ray
Lithology
Depth in meters
Callovian
250
Bajocian/
Bathonian
Migrated Data
200
Combining all possible solutions from all traces result in constructive
interference where reflectors are located
© 2019 Halliburton
Figure 3> A) Diagram showing the location of wave paths between a source and a receiver when a dipping bed occurs in the
subsurface; B) A model for unmigrated data with two dipping beds; and C) The effect of constructive interference in migrating
traces to accurately position the dipping bed.
basement.” This is the depth below which stratigraphic character cannot be resolved. This need
not correspond to a transition from sedimentary to crystalline successions, especially if reflective
features, like sills or lava flows, occur.
2150
150
2200
100
Toarcian
Bajocian
2100
a)
Exploration Handbook | 35
2250
50
WELL TO SEISMIC TIES
This integration of well and seismic data can be achieved in a number of ways that include analysis
of check shots and/or sonic logs data. Well and seismic data can also be linked by creating synthetic
seismograms from sonic and density logs (e.g. McQuillan et al., 1984; Ashcroft, 2011). Synthetic
seismograms are created by calculating the reflection coefficient where changes in lithology occur.
2300
Pleinsbachian
0
Hettangian/
Sinemurian
a
b
© 2019 Halliburton
c
Figure 5> Diagram showing the vertical resolution of seismic data compared with
stratigraphy from the Beatrice Field of the North Sea. The sine wave has a frequency of
30 Hz and a medium velocity of 2000 m/s (after Bertram and Milton, 1996). Schematic of
the Houses of Parliament (U.K.) is shown for comparison.
“Conceptual uncertainties
can be common in
interpreted seismic data.”
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