American Oil and Gas Reporter - September 2015 - 84

SpecialReport: Reservoir Characterization
Figure 1C displays the PCA results,
but this time the second highest eigenvalue
was selected and produced a different
set of seismic attributes. The top seismic

attributes from the second principal component include instantaneous frequency,
thin bed indicator, acceleration of phase,
and dominant frequency, which total al-

FIGURE 2
A)

N

S

B)

C)

This shows SOM A results on
a north-south in-line through
the field. 1A shows the original
stacked amplitude. 2B shows
SOM results with associated
five-by-five color map displaying all 25 neurons. 2C shows
SOM results with four neurons
selected that isolate attenuation effects.

Attenuation

FIGURE 3
A)

N

S

B)

C)

Gas/Oil Contact
Oil/Water Contact
Undrilled Flat Spot

84 THE AMERICAN OIL & GAS REPORTER

SOM B results are shown
on the same in-line as Figure 2. 3A is the original
stacked amplitude. 3B
shows SOM results with
associated
five-by-five
color map. 3C is the SOM
results with a color map
showing two neurons that
highlight flat spots in the
data.

most 70 percent of the variance of the 18
instantaneous seismic attributes analyzed.
These results suggest that when applied
to an SOM analysis, perhaps the two sets
of seismic attributes for the first and
second principal components will help
define different types of anomalous features or different characteristics of the
same feature.
The first SOM analysis (SOM A) incorporates the seismic attributes defined
by the PCA with the highest variation in
the data, i.e., the five highest percentage-contributing attributes in Figure 1B.
Several neuron counts for SOM analyses were run on the data, and lower count
matrices revealed broad, discrete features,
while the higher counts displayed more
detail and less variation. The SOM results
from a five-by-five matrix of neurons
(25) were selected for this article.

Detecting Attenuation
The north-south line through the field
in Figures 2 and 3 show the original
stacked amplitude data and classification
results from the SOM analyses. In Figure
2B, the color map associated with the
SOM classification results indicates all
25 neurons are displayed. Figure 2C
shows results with four interpreted neurons
highlighted.
Based on the location of the hydrocarbons determined from well control, it
is interpreted from the SOM results that
attenuation in the reservoir is very pronounced. As Figures 2B and 2C reveal,
there is apparent absorption banding in
the reservoir above the known hydrocarbon
contacts defined by the wells in the field.
This makes sense because the seismic
attributes employed are sensitive to relatively low-frequency, broad variations in
the seismic signal often associated with
attenuation effects.
This combination of seismic attributes
employed in the SOM analysis generates
a more pronounced and clearer picture
of attenuation in the reservoir than any
of the seismic attributes or the original
amplitude volume individually. Downdip
of the field is another undrilled anomaly
that also reveals apparent attenuation effects.
The second SOM evaluation (SOM
B) includes the seismic attributes with
the highest percentages from the second
principal component, based on the PCA
(see Figure 1). It is important to note that
these attributes are different from the attributes determined from the first principal
American Oil and Gas Reporter - September 2015

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