Geology Reference
In-Depth Information
a)
b)
c)
Seismic Lithofacies
Elastic parameter pdfs
Parameter correlations
Shale
V
p
Shaley sand
V
s
Water sand
Oil sand
Gas sand
Correlations
e.g. V
p
and V
s
,
Density and V
p
Density
V
p
AI
d)
e)
f)
Stratigraphic context
and facies ordering
Variograms: vertical
and lateral
Depth Trends
Lateral
Vertical
γ
distance
AI
V
p
/V
s
distance
Figure 5.49
Elements of the rock model.
seismic trace inversion (
Chapter 9
) and net pay
analysis (
Chapter 10
).
sectionfromanareainwhichthereservoirsand-
stones are relatively widespread and thick is shown
in
Fig. 5.50a
. A top sand interpretation has been
made with a consistent black peak (hard event),
tying the water wet well down-dip to the right of
the section (
Fig 5.50a
). A basic workflow was rap-
idly implemented using the data from the down-dip
well, comprising fluid substitution of water wet
sands to hydrocarbon (nearby fields provide infor-
mation on likely fluid parameters), extracting aver-
age properties from the logs and generation of a
single interface AVO plot. The AVO plot (
Fig
5.50b
) suggests that at the effective angle of the
seismic the presence of hydrocarbons would result
in a dramatic dimming of the top reservoir reflec-
tion. So, either the initial interpretation is correct
andtheprospectiswaterfilledorthereisanother
interpretation.
The AVO plot suggests that an oil water contact
would have a similar polarity and level of amplitude
5.4.1 Examples of rock model applications
The time and effort put into generating a rock physics
database and Rock Model to some extent depends on
the application. In partially explored areas it is often
the case that a relevant seismic model can be estab-
lished fairly quickly by an analysis of wells close to the
prospect. In such cases it can reasonably be assumed
that the stratigraphy and rock types have been
adequately sampled in the offset wells. In other cases,
such as regional evaluations or detailed statistical
applications, a considerable amount of time is spent
in generating the rock model and understanding
variance.
Figure 5.50
illustrates an example of an applica-
tion of a simple seismic rock model in interpreting a
potential oil prospect. A migrated full stack seismic
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