American Oil and Gas Reporter - November 2016 - 52

SpecialReport: Oil & Gas Computing
slant stack (LSS) operators, optimally
designed for each primary ray pair associated with a given source-image/pointreceiver path, and the corresponding seismic data event. The LSS is applied in
the direction of the horizontal "slowness"
components of the arriving rays at the

acquisition surface, where the size of
the LSS (the number of traces involved)
is computed independently for each ray
pair from its first Fresnel zone (a region
defining the lateral resolution of seismic
data).
Therefore, primary reflection events

FIGURE 2
Full-Azimuth Surface to Subsurface Mapping

Full-azimuth reﬂectivity
and directivity displayed as
5-D gathers

Full-azimuth reﬂectivity
and directivity displayed as
3-D gathers

Full-azimuth reﬂectivity
and directivity displayed as
2-D gathers

FIGURE 3
Full-Azimuth Directivity Gather with Depth,
Dip and Azimuth Energy Distributions

15
30

Specularity
0.0

45

Azimuth (deg)

240

Dip (deg)

60

0.1

60
30

Azimuth 90°

270

75
0

330

300

0.2
0.3
0.4

Azimuth 270°

0.5

sharing the same travel time and the same
surface directivity as the traced ray pairs
are emphasized (highly weighted), while
all other events (considered as noise) are
attenuated simultaneously.
In the second approach, the fullazimuth directivity gathers are used to
identify the respective energy distributions
of primary and multiple events in both
dip and azimuth. Special operators are
designed to subsequently remove the multiples with different dip and/or azimuth
energy distributions from the primaries.
This approach can be quite effective at
attenuating interbed multiples, particularly
if there is any structural separation of
primary and multiple events.
Figure 3 shows a full-azimuth directivity gather with energy distributions
over depth (vertical axis), dip and azimuth.
Contributions of energy can include primary specular energy, diffraction energy,
and multiple energy.
These approaches are highly complementary, and in practice, are used together
to optimize the removal of multiple energy,
where the full-wave-field imaging solution
coupled with a predetermined set of conditions is used to isolate primary energy
from multiples. The predetermined set
of conditions can be unique to the primaries and can include, for example, specific arrival directions, travel times, directions of reflected signals, angles of
reflection, arrival locations on a free surface, or any other suitable conditions or
combination of conditions.
Field Example
Figure 4 shows a comparison of multiple suppression efficiencies between a
Kirchhoff prestack depth migration (top)
and full-azimuth imaging and decomposition (bottom) focused on multiples attenuation along a Jurassic and Paleozoic

0.6
Azimuth 0

0.7

Coming In December

0.8

Last winter was the second
warmest on record, but this winter is
expected to be a different story. Temperatures are forecast to return to
more normal levels, increasing heating degree days by 12 percent yearto-year. The Natural Gas White
Papers analyze all the implications,
and consider factors such as growing
demand in electricity generation and
industrial sectors.

1.2
1.5
0

1.8
20

2.1

40

2.4
2.7
3.0
3.3

60
80
Dip (deg)

Depth (km)

52 THE AMERICAN OIL & GAS REPORTER

0.9
1.0
American Oil and Gas Reporter - November 2016

Table of Contents for the Digital Edition of American Oil and Gas Reporter - November 2016
