Toward More Accurate Reservoir Definition
5D full-azimuth angle domain diffraction imaging provides new insights on fracture distribution
Contributed by Paradigm
I
n an effort to obtain a more accurate definition of the
reservoir, E&P companies have made huge investments
in acquiring rich seismic data with wide azimuth and long
offset, especially in fractured and subsalt reservoirs. Traditional seismic image volumes generated from these surveys
capture the composite response of the subsurface to wavefronts propagating from all subsurface angles and from all
directions or azimuths.
While these volumes of data are appealing to the seismic interpreter in defining major structural and stratigraphic events, small faults, discontinuities, and other
reservoir heterogeneities are often masked or lost in conventional seismic imaging procedures.
Because standard seismic imaging procedures integrate a large number of seismic events from energy arriving at different angles and all possible dips at each image
point, smearing of the image along key subsurface objects
can occur, especially in complex geological areas characterized by faults, pinchouts, and material discontinuities.
Consequently, the standard discontinuity attributes (e.g.
coherence curvature, fault-likelihood) can suffer from
inaccuracy, instability, and considerable uncertainty when
applied to poststack image volumes.
Full-azimuth angle domain imaging reorganizes surface-recorded seismic data in physically meaningful ways
to generate higher quality images and information that are
not obtainable from conventional methods.
The technology recovers a full spectrum of azimuth
data in-situ and in-depth, much the way borehole tools
sample the subsurface. The procedure avoids the problems associated with the traditional approach of sectoring
surface-recorded seismic data in order to obtain subsurface properties that vary with azimuth. It also avoids
the problem of early integration or summation (stacking) of seismic amplitude data, allowing for the recovery of high-resolution subsurface features. These features
can have a substantive impact on the production of what
would otherwise appear to be homogeneous and continuous reservoirs.
In full-azimuth angle domain imaging, seismic surface data is decomposed and organized into five-dimensional data objects (prestack data) that fully describe
SEG DAILY NEWS I
both the directivity (dip
and azimuth) and reflectivity (opening angle and
azimuth) of subsurface
events. From this richly
“decomposed”
seismic
data, geophysicists can create specular and diffraction
images, where the specular
images emphasize structure continuity and the diffraction images emphasize
small-scale discontinuities.
Diffracted energy can
carry the signatures of
high-resolution subsurface
stratigraphic and structure
features. Standard seismic
Comparison of Coherence Cube applied to poststack seismic image (left) versus
imaging operators and pro- full azimuth diffraction imaging (right). Note the preservation of reef features and
cedures are preferentially associated faulting in the diffraction imaging. Data courtesy of Sintez Petroleum.
biased against this diffracevery common image gather. By carrying this process
tion energy and consequently cannot recover the subsurout in the full azimuth local angle domain, the energies
face features that generated them.
associated with high-resolution diffraction events are
Paradigm has developed a patented seismic depth
preserved. Consequently, even low energy diffraction
imaging system (EarthStudy 360) that maps and decomdata sources can be both isolated and emphasized in
poses surface-recorded seismic data into subsurface mulspecial workflows. Note that this type of structural or
tidimensional prestack image gathers. This mapping and
stratigraphic information is routinely derived from post
decomposition technique is carried out with a rich, botmigration image volumes, created either by ray-based
tom-up diffraction ray-tracing operator in an in-situ
Kirchhoff or wave equation migrations, using local
reference system referred to as the local angle domain
coherent event analysis or structure-oriented filters. The
(LAD). Because the EarthStudy 360 local angle domain
images, however, are preferentially biased towards the
migration retains dip information, filters can be designed
specular energy.
to enhance or attenuate the higher amplitude reflectors
While improved fault recovery and imaging is a natand enhance the reflections or diffractions in the imaged
ural
outcome of the process, diffraction imaging also can
data, respectively. These reflection/diffraction events can
reveal
high-resolution heterogeneities in a reservoir that
then be stacked to give reflection/diffraction migration
are
not
recovered in standard seismic imaging workflows.
volumes that can be co-rendered for improving the interThese
images
can reveal controlling stratigraphic features
pretation process.
that
can
influence
field development and drilling deciThe power and efficacy of the implementation is
sions.
that the images are computed from full azimuth preFor more information, visit Paradigm at booth
stack data based on a visible discrimination from
2808.
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continuous or specular energy at every depth point of
WEDNESDAY 21 OCTOBER 2015
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