Gravity data processing
| Exploring for Oil and Gas Traps | |
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| Series | Treatise in Petroleum Geology |
|---|---|
| Part | Predicting the occurrence of oil and gas traps |
| Chapter | Applying gravity in petroleum exploration |
| Author | David A. Chapin, Mark E. Ander |
| Link | Web page |
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Routine processing techniques
Gravity data as measured must be corrected for the earth's field.[1] There are five categories of corrections.
| Correction | Definition | Key Input Parameter(s) |
|---|---|---|
| Latitude | Whole-earth effect at sea level related to the shape and the spin of the earth | Latitude |
| Free air | Correction because the observation is not at sea level | Elevation |
| Bouguer | Free air correction to add back the rock between the observation and sea level | Elevation & surface density |
| Terrain | Simplified assumptions of Bouguer correction in high-relief areas | Detailed topography & surface density |
| Eötvös | Gravity collected on moving platforms has different angular velocities than the earth's for dynamic gravity | Platform's velocity & heading |
One of the most critical parameters in typical surveys is the high accuracy needed in elevation control. Submeter accuracies are usually necessary, except for marine surveys which are, by definition, collected at sea level.
Interpretive processing techniques
After obtaining either free air gravity or Bouguer gravity, subsequent processing may be needed to enhance or suppress various geologic effects. For example, Bouguer gravity naturally has lower values over higher elevations and higher values over deep ocean basins because of variations in the crustal thickness, or isostasy. An isostatic correction to suppress this deep effect can be made if the data set is large enough.[2] In smaller data sets, typically a long-wavelength surface can be removed from the data to suppress this effect. Other interpretive processing to enhance certain anomalies includes the following:
- Band-pass filtering—selecting a range of wavelengths to display
- Derivatives—edge-enhancing processes that tend to emphasize the shorter wavelength anomalies
- Upward or downward continuation—a process that attenuates or deattenuates data to simulate what might be observed at different vertical datums
Collectively, these are all termed regional or residual operators. Many different types are useful for different purposes.
See also
- Gravity basics
- Interpreting gravity measurements
- Models of gravity anomalies
- Examples of gravity applications
References
- ↑ Chapin, D. A., 1996a, The theory of the Bouguer gravity anomaly: a tutorial: Leading Edge, May 1996, p. 361–363.
- ↑ Chapin, D. A., 1996b, A deterministic approach towards computing isostatic gravity residuals: case history from South America: Geophysics, vol. 61, no. 4, p. 1022–1033, DOI: 10.1190/1.1444024.
External links
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