Geology Reference
In-Depth Information
Full stack amplitude change
Water saturation change
Red-blue
Sw
Hardening
0.5
Softening
0.25
Reservoir pressure change (psi)
Gas saturation change
PSI
Sg
3000
0.05
1500
0.03
0
Figure 10.30
Schiehallion Field time-lapse mapping using a multi-attribute calibration of production data (after Floricich et al.,
2006
). The
attributes used in this example were far amplitude, intra-reservoir time-stretch (i.e. time-shifts computed in a window below the reservoir
minus time-shifts computed in a window above the reservoir), near amplitude, full amplitude and instantaneous frequency.
+2
months
+5
months
+9
months
+13
months
+19
months
+31
months
Figure 10.31
Vertical seismic sections
from baseline and monitor surveys in the
Duri Field, Indonesia. The yellow lines
show the top and base of the steam
injection interval. Note how the reflection
time of the base increases as the
steamflood progresses in time, whilst the
data do not change above the steam
zone (after Jenkins et al.,
1997
).
Baseline
workflow for example by the introduction of Bayesian
concepts (e.g. Floricich et al.,
2006
).
Travel-time differences have typically been used to
analyse time-lapse situations with large changes in fluid
compressibility. For example,
Fig. 10.31
illustrates
travel-time changes on base reservoir reflections with
progression of a steamflood. However, timing effects
can also be associated with geomechanical changes in
the reservoir (i.e. porosity reduction) and in the over-
burden as a stress response to pressure depletion in the
reservoir. These phenomena have been described from
a range of producing fields including North Sea Chalk
fields which compact during production (e.g. Nickel
et al.,
2003
; Herwanger et al.,
2010
) and high pressure/
high temperature fields (e.g. Hatchell and Bourne,
2005
; Hawkins et al.,
2007
).
Figure 10.32
shows the
time-lapse time-shift effect related to subsidence on
Ekofisk field (after Nickel et al.,
2003
). Geomechanical
time-lapse effects can be modelled using rock physics
relationships (e.g. Hatchell and Bourne,
2005
) and
these can be compared with the time-lapse seismic
result (
Fig. 10.33
). Time-shifts are now being specific-
ally incorporated into time-lapse inversion methodolo-
gies (e.g. Bhakta and Landro,
2013
).
Confident identification of time-lapse effects gen-
erally requires high levels of seismic repeatability.
244
