How do you
convince "a non believer," in a short article with only a few static
Figures, the need for visualization?
Within
some companies the value of integrating visualization techniques
into the exploration workflow is well documented (pun intended).
In these companies, the answer is along the lines of: "In order
to get a well drilled, it is required by those whose money we are
using to drill the well, since it has shown repeatedly to be an
excellent risk reducer and a very good return on investment."
Visualization
encompasses the software, hardware and workflow combination that
allows trained and experienced interpreters to rapidly investigate
— and communicate to others — the internal heterogeneities of
their 3-D data volume.
All three
components are important, but the workflow element is probably the
most important. It is the workflow that allows you to answer the
questions you need to ask of the data. If you choose the wrong workflow,
some questions will remain unanswered, or poorly answered.
The ability
to use a particular workflow effectively depends upon the software
package employed. For example, package A is better than package
B for quickly comparing multiple attributes on a particular section
of data. Yet, package B's ability to opacity filter large volumes
is significantly better than package A's for identifying regional
amplitude anomalies.
The growing
amount of available 3-D data is one reason an interpreter needs
to employ visualization techniques. On a worldwide basis (excluding
North America), numbers published by the IHS Energy Group in "First
Break" indicate that from 1991 to 2002 the cumulative surface area
covered by 3-D seismic data doubled every 2.5 years. By the end
of 2001, the equivalent surface area of this cumulative seismic
data was larger than the state of Alaska.
If you
assume that a full stack and three additional attribute volumes
(such as a near-, mid- and far-stack volume) need to be interpreted,
then by the end of 2002 these combined volumes could cover the entire
United States. The speed, efficiency, completeness and multiple
workflows available from visualization tools are required to keep
up with the growing data volumes.
Moore's
Law is yet another reason you need to use visualization techniques,
and continually upgrade your computers and graphics system. Moore's
Law implies that if you upgrade your visualization hardware every
three years you will catch up on the growth of the 3-D data volume.
Your graphics and computing power will increase by ~4x, while the
data volume has only increased by ~2x.
If your
competitors are using visualization tools and continually upgrading
their hardware and you are not, how much farther behind are you
falling?
However,
the most compelling reason that you need to use visualization tools
is that if you don't, you probably will miss important features
of your data volume, such as detailed depositional patterns and
large regional flat spots.
Figure
1 contains 12 sub-images showing changing depositional patterns.
The first sub-image is of the volume-sculpted package. The other
11 images are proportional (stratal) slices through this package.
Slices (3) through (11) were taken proportional distances from the
top and bottom of the two bounding surfaces (2) and (12).
The depositional
patterns in the proportional slices are not apparent on either of
the bounding surfaces, nor are they readily apparent in the volume
rendered sub-volume.
Such details
are important as they indicate possible flow boundaries or conduits
as well as give clues where other sands might be deposited.
A volume
rendering of the largest amplitudes found in the mid-angle stack
over an undeveloped West Africa field is shown in Figure
2. This is an end on view of a ~300-square-kilometer survey.
The sands of the field, which are expected to contain in the range
of 500 bcfg to 1 tcf gas within the limits of the 3-D survey, are
between 2,400 to 2,600 ms.
The flat
spot at 2,100 ms is hard to miss — however, at least seven different
evaluation teams did not identify it as a drilling target. Clearly
these teams did not generate a similar display. Most of these teams
concentrated their efforts on the slightly deeper (250+ ms) objective
known to contain hydrocarbons and believed to be part of a giant
regional stratigraphic trap.
How many
of us don't have or take the time to explore the volume above or
below our current objective? Do you know what you are missing?
A thick,
volume-rendered, opacity-filtered time-slice around 2,100 ms, again
just showing the largest amplitudes, is provided in Figure
3. The five wells, drilled for the deeper target, missed hitting
the 60-square-kilometer flat spot, even though it covers about 20
percent of the survey. The two wells that clipped the edge of the
flat spot should be investigated for oil shows.
The AVO
nature of this event is illustrated with Figure
4. It is not a "textbook" example of a fluid contact. The "reservoir
sands" are hard to discern on the vertical sections, they don't
have the textbook behavior on either side of the "fluid contact,"
and the contact appears to locally "change phase." The "contact"
also appears to have some localized "velocity pull down."
However,
until the gathers are evaluated for proper processing and rock property
modeling has been done, a hydrocarbon affect should not be ruled
out.
If the
flat spot is a fluid contact, then optimistic approximations to
the reservoir geometry and properties imply over five billion barrels
of oil in place within the limits of the survey. Figure
3 indicates that the flat spot should extend beyond the survey
limits.
If the
right visualization tools and workflow were utilized earlier in
the project, slight modifications to two of the drilled well paths
could have allowed testing of this potential reservoir.
So is this
a missed billion-barrel field? Only a well will tell.
For those
of you who still don't think you need visualization, you might be
right, for in the words of Edward Deming:
"It is
not necessary to change. Survival is not mandatory."