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The
Future of
Borehole
Seismic - by Bob Hardage |
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I became interested in VSP
in the 1970s. At the time, I was responsible for
implementing seismic stratigraphy technology at Phillips
Petroleum Company and was searching for an optimal way to
define the depth coordinates of seismic sequence
boundaries interpreted from surface-recorded seismic data.
My initial interests in VSP were limited to distinguishing
primary reflections from multiples and to positioning
depth-based geologic detail at its proper seismic
image-time coordinates across our seismic stratigraphy
prospects. Numerous other VSP applications were developed
by many people once VSP technology was established in the
early 1980s via textbooks, short courses, journal
articles, and contractor investments in equipment and
software.
We are now three decades later in developing and applying
VSP technology. In many ways, the technology is mature. We
can now deploy large vertical arrays with good sensor
coupling at all stations, acquire data at high rates,
process data at the well site, and image complex
structure. What then does the future hold?
First, the VSP applications that have been demonstrated
and proven during the past 20-plus years will make VSP an
essential part of most future energy exploration and
exploitation programs. Depth-based geology will still have
to be calibrated to time-based surface seismic data,
reservoirs will still need to be imaged and characterized
in detail, and fluid movements will still need to be
monitored over calendar time. VSP offers valuable
assistance in all of these areas.
Second, two technologies will probably become the growth
areas of VSP and dominate its future. One of these focus
areas will be VSP support of surface-based multicomponent
seismic technology. The second emphasis will be
high-resolution 3D imaging of critical stratigraphic
intervals.
Multicomponent seismic technology is thought by many to be
a revolution in our thinking that will revitalize the
seismic industry worldwide. I am one who believes
multicomponent seismic data will be the business driver of
future seismic services. Once multicomponent seismic data
is acquired, people soon discover that each mode of the
elastic wavefield has a different reflectivity at
subsurface interfaces. As a result, each shear (S) mode
(there are several) provides a different picture of
seismic sequences and seismic facies over portions of
seismic image space from that of its companion S modes,
and all of these S images differ from the compressional
(P) image that has been the sole basis of seismic
stratigraphy for decades. If acquisition and processing
have been done correctly, the image constructed from each
independent mode of the elastic wavefield has equal value
and validity. However, to utilize these several P and S
images, each image has to be calibrated to depth-based
geologic control to understand the significance of the
different sequence boundaries and facies domains that are
expressed in the image space of each wave mode.
Good-quality multicomponent VSP data that has captured the
full elastic wavefield and then expressed all P and S
modes as both depth-based and timed-based images is the
best way to calibrate subsurface geologic control to each
image option provided by surface-based multicomponent
seismic data.
Thus VSP technology must, and will, move into the arena of
analyzing the basic physics and geological importance of
multicomponent seismic imaging. The result will be that
geoscientists will begin to rely on VSP to help them apply
seismic stratigraphy principles to images provided by the
full elastic wavefield rather than to limit this valuable
science to information provided by only P-wave images.
Regarding 3D imaging, the second growth area for VSP, two
observations need to be made. First, 3D technology has
been the dominant factor that has driven the seismic
contractor business for the past 15 years. The result is
that geoscientists now accept nothing less than
high-quality 3D seismic images when they have to evaluate
prospects and characterize reservoirs. Second, almost all
VSP imaging has been limited to 2D data, which has
lessened the appeal of VSP to many potential users.
VSP technology has to expand into the 3D realm to maintain
its vitality, increase its value, and expand its
acceptance. The challenges are to develop field procedures
that make the acquisition costs more attractive and to
develop better algorithms for converting these data into
3D images. These two challenges can be met, but VSP
contractors will need the support of the VSP client
community to justify the costs that will be incurred as 3D
acquisition and processing are optimized. When 3D VSP
acquisition becomes cost effective and 3D VSP imaging
becomes robust and reliable, clients will probably abandon
2D VSP technology just as they have abandoned 2D
surface-based seismic technology.
I am pleased to see that Baker Atlas and CGGVeritas are
focused on improving the future of VSP, as is evidenced by
the numerous technical advances they are now publicizing
and the formation of VSFusion. I am honored to be asked to
share my personal views on the future of VSP technology.
Providers of VSP services need faithful clients who will
provide a stable revenue income so investments can be made
in next-generation equipment and software.
Bob A. Hardage
Bureau of Economic Geology
The University of Texas at Austin
Austin, Texas |
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