Print this page
Click to view article as PDF
GCValue in Visualization*
By
Tracy J. Stark1
Search and Discovery Article #40133 (2004)
*Adapted from the Geophysical Corner column in AAPG Explorer, June, 2004, entitled “Why Do We Need to Have Visualization?” and prepared by the author. Appreciation is expressed to the author, to Alistar R. Brown, editor of Geophysical Corner, and to Larry Nation, AAPG Communications Director, for their support of this online version.
1STARK Research, Plano, Texas ([email protected])
Introduction
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 investigate rapidly – 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.
|
|
Case for VisualizationThe 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 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.
ExamplesFigure 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 have been 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 The flat spot at 2100 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 2100 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 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 do not have the textbook behavior on either side of the “fluid contact,” and the contact appears locally to “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 effect 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
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.” |
