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PSFrom collection to utilization: Outcrop analog data in a 3D world*
By
John B. Thurmond1
Search and Discovery Article #40126 (2004)
*Adapted from poster presentation at AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.
1University of Texas at Dallas ([email protected])
The collection of
three-dimensional data from outcrops is playing an increasingly important role
in reservoir characterization studies. There are a variety of techniques that
can be used to acquire three-dimensional data from outcrops, and each should be
applied individually or in concert to collect data in specific circumstances.
The current suite of emerging methods typically used in outcrop-scale
measurement includes traditional surveying, direct GPS measurement, laser
scanning (LIDAR), photogrammetry, and photorealistic 
mapping
(texture draped
geometry). Depending on the morphology, setting, and particular data needs of a
specific outcrop, different methods can be used to acquire data. Case studies of
individual outcrops will be shown to illustrate the problems and benefits of
several of these methods.
Once three-dimensional data is collected, utilizing the data can present its own set of challenges. Each collection method produces a different type of data, each of which requires a variety of processing and interpretation methods to utilize effectively. In most cases, there is also the need to integrate data from a variety of sources into a single interpretable data set. Again, case studies provide specific illustrations of effective methods that have been used in various projects to produce reservoir models from a variety of environments, including deep-water channel systems, heavily faulted fluvial environments, and carbonate build-ups.
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uAbstractuPhotorealistic outcrop capture
uAbstractuPhotorealistic outcrop capture
uAbstractuPhotorealistic outcrop capture
uAbstractuPhotorealistic outcrop capture
uAbstractuPhotorealistic outcrop capture
uAbstractuPhotorealistic outcrop capture
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Figure Captions
MethodsThe most
straightforward method for Normally, Real-Time Kinematic GPS systems are used, which provide an accuracy of approximately 2cm. Due to the practicalities of efficiently walking on a geologic surface, the normal accuracy is about 50 cm.
Advantages: High accuracy (50 cm or less). Accurate data distribution (no surface, no data) eliminates “interpolation” problems.
Disadvantages: Slow (5-10 km per day).
Re-interpretation can require
re-
Laser Rangefinder Often, it is not physically possible to “walk” on a stratigraphic surface, so other techniques are required. Reflectorless Laser Rangefinders, coupled with high-precision GPS receivers, provide the opportunity to capture data from such locations. These systems integrate an EDM for distance measurement with a digital compass and inclinometer, so 3D position can be measured remotely. However, this technique requires surfaces that are visible from a remote location.
Advantages: Fast.
Disadvantages: Lower accuracy (varies with distance). Encourages interpolation/extrapolation.
Re-interpretation can require
re-
Photorealistic Outcrop Capture (Figures 7 and 8) Using a scanning laser system, coupled with a high-accuracy GPS system, it is possible to scan the topography of an outcrop with a high degree of accuracy. Digital photographs can then be accurately mapped to the topography, which provides an accurate, three-dimensional model of the outcrop. This model can then be interpreted in 2D (on the photographs) or in 3D (on the model), and re-interpreted as often as necessary. Some laser systems provide the capability of scanning color simultaneously with distance, but the data sets are incredibly difficult to work with, even with the most advanced 3D workstations available. However, 3D geometry combined with texture data from photographs renders extremely quickly, even on laptops (ask for a demo!).
Advantages: Fast. High accuracy (5-10cm pixel error (!)). Provides images with data, so interpretations are believable. Data sets can be re-interpreted as paradigms change.
Disadvantages: Expensive equipment required. Processing can be intensive.
CarbonatesLocation: Last Chance Canyon, Guadalupe Mountains, New Mexico (Figures 5 and 6) Problem:
Excellent 3D exposures of a mixed carbonate and siliciclastic system.
Antecedent topography is an important control on subsequent facies
deposition.
Techniques: Currently, only GPS Results: Current: 3D geologic model of (hydrodynamic?) mud-mounds. Model provides evidence for re-interpretation of processes controlling mud-mound deposition. Future: Interpreted photorealistic model of Last Chance Canyon. This will provide a framework for building a 3D geologic model of the canyon, which will be an excellent research and teaching data set.
SiliciclasticsLocation: Eocene Ainsa II deepwater channel and lobe complex of the South-Pyrenean Foreland Basin, Spain (Figures 7, 8, 9, 10, and 11) With: Ole J. Martinsen and Tore M. Løseth, Jan Rivenaes, and Kristian Soegaard, Norsk Hydro Research Centre Problem: These deep-water siliciclastics are an excellent analog for active production fields in offshore Angola. Accurate 3D data captured from outcrop facies relationships is used to build a reservoir model, which can help predict heterogeneity in the subsurface and will also make an excellent teaching data set. Techniques: Numerous integrated photorealistic models were used to collect accurate 3D representations of the outcrop. Surfaces were interpreted in an immersive visualization environment (a CAVE) and, combined with spatially accurate 3D structural models, produced by the University of Barcelona. Results: A reservoir model was produced from the 3D data acquired from the outcrops.
Fault
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