American Oil and Gas Reporter - May 2015 - 77

SpecialReport: Study In Geophysics
time-based view of production.
Approaching microseismic from a processing, rather than "earthquake analysis"
perspective, he says the company uses
the entire microseismic signal instead of
hypocenters only. Using the whole signal
allows interpreters to identify activity or
movement on faults and fractures that
might otherwise be overlooked.
"Traditional approaches look for one
really loud event and try to locate its position in x, y, z space," says Peebles.
"Using a depth migration approach, it is
possible to pull out additional geologic
information that is otherwise buried in
the signal."
Microseismic data are recorded for
hours or even days, creating thousands
of 3-D volumes at different points in
time. Peebles says Global Geophysical's
patented processing method stacks these
3-D volumes and the total trace energy
over extended periods, adding tremendous
sensitivity and imaging surfaces. "When
the many hundreds of volumes are stacked,
it becomes apparent where the cumulative
acoustic activity is over the whole period,
highlighting fracture areas," he asserts.
Microseismic And 3-D Reflection
With improvements in recording technology and the advent of autonomous
nodal recording systems, both microseismic and traditional reflection seismic can
be recorded using one system, Peebles
says. By recording microseismic during
quiet times of traditional 3-D seismic acquisition, two different but complementary
datasets of a single rock volume can be
imaged. Processed separately, he says,
the microseismic delineates active natural
faults and fractures, while the 3-D seismic
provides rock properties and surfaces.
"Combined seismic/microseismic
analysis helps identify frac stages that
are likely to be unproductive, potentially
resulting in significant cost savings in
completions," says Peebles, adding that
integrating microseismic and 3-D reflection seismic provides guidance through
the completion and design phases of production.
According to Peebles, there are various
applications to integrated microseismic
and 3-D seismic data. For example, fractures can provide additional insight into
faults. "Faults under stress may have
fractures active around them," he illustrates. "Combined with other insights
from attributes, identifying these fracture
swarms could indicate a hazard to avoid

One of the significant developments in marine seismic surveying is the capability to detect marine mammals by position and species. A listening device developed by Sercel
that can discriminate the frequency range associated with different species displays onscreen the distance and bearing from the seismic vessel of mammal life in the water.

or a boon for production."
Peebles says integrating microseismic
and 3-D seismic presents an opportunity
for geophysicists to identify the most important characteristics of a given well,
informing drilling, completion and production decisions.

Marine Surveying
Significant developments in marine
surveying run a gamut, suggests Robin
Ellis, vice president sales and marketing
at Sercel in Houston. One is more accurate
placement of receivers. "The advent of 4D surveys requires operators to reshoot a
survey and compare the images with those
from a previous shoot," he comments.
He says this enables them to see
changes in the reservoir resulting from
production, such as the effect of an injection program on reservoir depletion.
To be successful, he points out, both
sources and receivers need to be in exactly
the same position they were in the previous
survey. But sea and current conditions
may have changed significantly. He says
real-time positioning systems account for
that and put sources and receivers in the
right place.
"It is extremely complex to synchronize
positioning and timing on multiple vessels," Ellis remarks. "Each acquisition
vessel may tow 12 or more eight-kilometer
seismic streamers, with each receiver
point in those streamers being positioned
in real time."
Given the increasing demand for environmental oversight, another significant
development is the capability to detect

whales and other marine mammals by
position and species, Ellis continues.
"This technology is unique in that it can
display onscreen the distance and bearing
from the vessel of mammal life in the
water," he describes.
Previously, he says, detecting marine
mammals involved listening devices with
an on-deck observer using powerful binoculars. The new technology delivers greater
precision and supports 24-hour operations.
"We integrate this technology directly
into our acquisition systems, using both
dedicated, specialized sensors and the
sensors in the seismic array itself," Ellis
says. "The technology also can be deployed as an independent array."
He describes the technology as a listening device that can even discriminate
the frequency range associated with different species.
Finally, advises Ellis, watch for accelerometers to make a big difference in
marine acquisition. He says these devices,
used in addition to standard hydrophones,
allow processors to calculate the direction
of arriving wave fronts. This, in turn, enables better differentiation of noise.
Processing is all about finding the
seismic reflection and signal. Noise is
introduced when the environment is not
uniform. "The seabed is not flat, the
ocean surface is not flat, and the subsurface
itself may be severely deformed," Ellis
illustrates. "The trick in processing is to
figure out the ray paths and use that
insight to remove noise."
At present, acquisition technology is
ahead of processing in this area, Ellis
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American Oil and Gas Reporter - May 2015

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