American Oil and Gas Reporter - January 2012 - 131

Tech Trends 2012
in Figure 3 through a coherence attribute
in gray scale co-rendered with the reflector
convergence displayed against a 2-D color
wheel. Vector convergence azimuth is
plotted against hue, while its magnitude
is plotted against lightness to produce
the color wheel. Sediments that are converging toward the southwest are colored
green while those converging toward the
northeast are shown in magenta. By integrating this image with Figure 2 (showing
rotation), the patterns can be interpreted
to indicate syntectonic deposition as the
grabens rotated, forming greater accommodation space in a given direction.
Figure 4 displays two arbitrary lines
(AA' and BB') through the same volume,
showing the infill of grabens. The change
in color is related to changes in accommodation space provided by the block
rotations. Sediments that have low convergence magnitude or that are nearly
parallel have been rendered transparent.

FIGURE 6
Coherence Time Slice as Horizontal Section Showing Channel System

Clastic Depositional System
A second example is of a clastic depositional system with minimal structural
deformation. Figure 5 illustrates the use

of reflector convergence in analyzing
stratigraphic relationships within a channel
with or without levee/overbank deposits
in terms of four cases:

FIGURE 5

Convergence

Amp

W

Coh
1.0

N

Positive

E

0

Negative

0.6

S

Convergence within a Channel
With or without Levee/Overbank Deposits

(a)

(b)

Convergence
N

(c)

W

E

S

(d)

Interpretation courtesy of Supratik Sarkar, University of Oklahoma

* Case A, where the deposition within
the channel shows no significant convergence;
* Case B, where the deposition within
the channel is such that the west channel
margin is converging toward the west
and the east channel margin is converging
toward the east (displayed in color to the
right with the help of a 2-D color wheel);
* Case C, where the deposited sediments within the channel are not converging at the margins, but the levee/overbank deposits converge toward the channel
(west deposits converge toward the east
and vice versa); and
* Case D, where both the strata within
the channel and levee/overbank deposits
are converging (this appears to be a combination of the B and C cases).
Note how the convergence shows up
in color using the 2-D color wheel as
displayed to the right in cyan and magenta
colors along the channel edges.
The computation of reflector convergence and the rotation about the normal
to the reflector dip attributes were carried
out for a suite of 3-D seismic volumes
from Alberta. Figure 6 depicts a 3-D
chair view with a coherence time slice
exhibiting a channel system, co-rendered
with reflector convergence attribute using
a 2-D color wheel. Within the area highlighted by the yellow, dotted-line ellipse,
an interpretation has been made keeping
JANUARY 2012 131
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