Geology Reference
In-Depth Information
a)
b)
c)
Difference
Baseline 1993
Monitor 1998
Figure 10.23
.,
2000
); (a) baseline (1993)
survey showing clear oil water contact, (b) monitor (1998) survey with no obvious flat reflection at original contact and brightening at top
Forties reservoir; (c) difference section.
An example of time-lapse seismic in a producing oil field (Gannet C Field, North Sea, after Koster
et al
2500
2500
3500
3000
2000
2000
2500
1500
1500
2000
1500
1000
1000
1000
OWC
500
500
500
OOWC
OOWC
OOWC
0
0
0
1998
2001
2004
(high definition)
0
6km
Figure 10.24
Time-lapse maps from Draugen Field, offshore Norway (1990-2004): RMS seismic amplitude difference (relative to 1990)
showing 1998, 2001 and 2004 water encroachment. There is a higher noise level for the 2004 map because of differences in acquisition
geometry. OOWC ΒΌ original oil/water contact (after Mikkelsen et al.,
2008
. Copyright 2008, SPE; reproduced with permission of SPE, further
reproduction prohibited without permission).
et al.,
2011
; Fehintola and Olatunbosun,
2011
). How-
ever, whilst there are a number of different types of
feasibility studies that can be carried out, it is not
always straightforward to determine the precise cost-
benefit. Time-lapse can confirm an existing percep-
tion of field performance or it might yield surprises
which can be used to adapt and optimise reservoir
development strategy.
Any change in the reservoir will have an effect on
acoustic behaviour; the main question for assessing
the feasibility of time-lapse is whether these changes
are large enough to be detected on seismic given the
perceived levels of seismic repeatability. Key reservoir
factors include:
state of consolidation,
239
porosity,
