Gravity data processing

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Exploring for Oil and Gas Traps
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

References

  1. Chapin, D. A., 1996a, The theory of the Bouguer gravity anomaly: a tutorial: Leading Edge, May 1996, p. 361–363.
  2. 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.

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Gravity data processing
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