American Oil and Gas Reporter - November 2015 - 52

SpecialReport: Oil & Gas Computing
the 5-D CIGs for both corrections and
seismic property extractions using "directivity driven" imaging. First, directivity driven 3-D semblance or "specularity" gathers are computed for each
5-D gather. The 3-D semblance values
are computed for each directivity bin
(dip/azimuth) over all depth points within
a given window. As the specularity
gathers are computed along the opening
angle/azimuth traces, they indicate the
coherent energetic directions of the

actual reflected events.
These directional gathers can be used
to form different types of weighted stack
filters. For example, to enhance structural
continuity of the subsurface reflectors,
the specularity values are used directly
as weighted stack coefficients. This results
in generating high-quality, full-azimuth
angle gathers that stack to the optimal
reflectivity image and considerably enrich
the information, and reduce uncertainty
in velocity model determination and am-

FIGURE 2
Eagle Ford Sections from Regular Stack (A)
And Specularity Enhanced (B) Volumes

FIGURE 3
Eagle Ford Depth Slices with Enhanced Specular Energy (Top)
And Enhanced Diffraction Energy (Bottom)
10,150 ft

11,500 ft
14,200 ft

52 THE AMERICAN OIL & GAS REPORTER

15,400 ft

plitude inversion analysis.
A further functionality is the separation
of multiple specular events that overlap
at a given imaging point, such as when a
coherently reflecting fault crosses layered
horizons, for example. Since the fault
may have a lesser overall seismic intensity,
simple stacking will mask the fault. Therefore, it is essential to consider multiple
specular reflections and to construct the
appropriate specular filter that will allow
for the unfolding of these unique seismic
events.
Another important option is "diffraction-enhanced imaging." Changes in the
elastic properties of subsurface rocks appear as seismic reflections. Diffractions
are generated by local discontinuities,
which act as a point source, whereas reflections are generated by an extensive
reflection boundary. This option involves
attenuating the high-specular energy, by
designing a filter that is one minus the
specularity values. Furthermore, duplex
waves, which exhibit directivity azimuthal
dependence, also can be extracted by
constructing the appropriate azimuthally
dependant semblance filter.
The important implication is that one
can generate different types of images,
each containing unique seismic information without rerunning the heavy computational process of the first stage.
Finally, the different images can be corendered to simultaneously visualize the
different geological characteristics.

Eagle Ford Examples
The examples presented in this article
are taken from the Eagle Ford Shale
play. Figure 1A shows the schema of
the mapping system with the surface
input parameters and the respective subsurface LAD domain parameters. The
5-D LAD gather is uniquely visualized
in the form of a 3-D display, where each
of the lateral axes combines two polar
angles: directivity dip/azimuth and opening angle/azimuth.
Figure 1B shows an example 5-D
gather for a specific in-line/cross-line coordinate from an advanced full-azimuth
angle domain imaging and analysis system
designed to image, characterize, visualize
and interpret the total seismic wave field
in all directions. The horizontal axes in
Figure B are γ (the opening angle and its
azimuth as a continuous spiral) and ν
(direction angle and its azimuth as a continuous spriral).

American Oil and Gas Reporter - November 2015

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