Lasers have been synonymous
with rock shows for years — but they are about to become important
for their rock shows.
Or, in the words of Scott Tinker (and his co-authors
Jerry Bellian, Charlie Kerans and Dave Jennette), lasers will play
a critical role in the 3-D seismic interpretation because lasers
will offer geoscientists the ability to see — and better understand
— outcrops in the same way that we currently examine 3-D seismic
surveys and derivative geologic models on workstations.
Tinker, director of the Texas Bureau of Economic
Geology, spoke in Denver at the recent annual 3-D Seismic Symposium,
sponsored by the Rocky Mountain Association of Geologists and the
Denver Geophysical Society.
He
did more than just talk, of course: He demonstrated through a slide
presentation how Bellian, Kerans, Jennette and other BEG researchers
have been using laser data to allow geologists to appear to fly
into a rock outcrop for an elevated view, or gain a perspective
not physically possible by removing canyon walls or obstructions.
"We're able to get into this world and fully interpret
the 3-D outcrop data," Tinker said, adding that working with 3-D
outcrops will revolutionize subsurface modeling.
"With this capability, we have a lot more understanding
of exactly what we're seeing."
Researchers' near-term goals are to use the high-frequency
3-D outcrop models to:
- Derive realistic 3-D synthetic seismic
data that can be used to examine seismic response as a function
of frequency.
- Test a range of seismic attribute sensitivities
to small changes in lithology, fluid and gas saturation.
- Create a portfolio of analogs for siliciclastic
and carbonate outcrop settings worldwide that give geoscientists
the ability to examine rock systems with clarity and precision
from their desktop.
The best news: Three-D outcrop studies that incorporate
land- and air-based laser, radar, electromagnetic and other remote
sensing technology will have a significant impact on subsurface
exploration and production success.
"The decades ahead promise a 4-D world of instrumented
producing fields and real-time data streaming," he said.
"Advanced recovery processes on producing fields
will require an even greater knowledge of the reservoir," he added,
"and new discoveries will be developed with fewer wells requiring
an increased understanding from remote sensing data."
'That's Fine Resolution'
Until
now, photo panoramas have provided the best means available for
studying outcrops — but their "retrieval capabilities are limited,"
Tinker said, bringing mixed results.
However, the portable, solar-powered Light Detection
and Ranging systems(LIDAR), built by Optech, can now scan 2,000
points per second for each point record x, y, z, and reflected intensity
values for outcrop faces up to one kilometer away, he said.
"We can shoot digital photos, (and) you can make
remarkably accurate renditions of canyon walls by patching it all
together and merging them to get continuous coverage of an outcrop
wall," he said. "This is just the beginning."
With this technology, tightly gridded reflection
intensity data are draped as a texture onto an optimized laser surface
model. These data can be interpreted directly as one would interpret
a black and white photopan, but the user can rotate the image to
achieve optimal perspective and accurately map the geology in real
space while still in the field.
"We are researching a range of information sources
that enhance the outcrop image, many of which may not be obvious
or even visible to the human eye," he said.
"That's a whole lot of information before you even
take a step on the rock."
Tinker's talk represented BEG research in progress
in laser technology applications and its 3-D analysis of carbonate
systems conducted by the Bureau's Reservoir Characterization Research
Laboratory (RCRL), and clastics systems conducted by the Clastics
Reservoirs Group.
Several major oil companies, large state oil companies
and independents currently sponsor the Bureau's Lidar studies.
These high frequency studies have yielded some remarkable
results, he said. Moreover, high-frequency laser data can be collected
and processed for most outcrop settings in just a few weeks, greatly
reducing post-processing and interpretation cycle time from conventional
photopan-based field methods.
"Most importantly," he added, "we retain the true
spatial relationships of the outcrop."
The initial product is a 3-D digital elevation model
with vertical resolution on the centimeter scale, which can be used
to:
- Visualize topography — and plan field
work, optimizing sampling strategies.
- Merge with digital photographs or other
remote sensing data.
- Interpret stratigraphic horizons, joints,
faults, macroscale diagenetic processes and bed-scale sedimentology.
- Drape and interpolate measured section
data.
- Calculate first derivative, second derivative,
reflection strength and other properties to help characterize
such things as faults and fractures, solution features and lithology.
- Provide the framework for input into 3-D
modeling.
Tinker backed up his words with slides of a channel
complex collected and interpreted by co-authors Bellian and Jennette
in northern Spain with an elevated view, proving the point that
"you can get different, sometimes incorrect, information by looking
at it on foot from the canyon floor.
"You can fly into the cliff," he said. "You're there
on that outcrop. It can make the field work a lot more intelligently
designed."
Even in a distant photo of an outcrop with some buildings
on top, the viewer can zoom in on details as small as the wristwatch
of a person standing on a balcony of a building.
"That's fine resolution," he said.
Jennette and Bellian will be presenting papers on
their research at the AAPG annual and international meetings in
Salt Lake City and Barcelona, Spain.