Difference between revisions of "Gravity anomaly models"

From AAPG Wiki
Jump to navigation Jump to search
Line 29: Line 29:
  
 
[[file:applying-gravity-in-petroleum-exploration_fig15-5.png|thumb|{{figure number|2}}]]
 
[[file:applying-gravity-in-petroleum-exploration_fig15-5.png|thumb|{{figure number|2}}]]
 +
 +
[[file:applying-gravity-in-petroleum-exploration_fig15-6.png|left|thumb|{{figure number|3}}]]
  
 
==Effect of depth==
 
==Effect of depth==
 
The amplitude of the gravity signal varies as a function of 1/depth<sup>2</sup> to the source. [[:file:applying-gravity-in-petroleum-exploration_fig15-5.png|Figure 2]] shows the gravity responses to a body of positive density contrast buried at different depths. The upper half of the diagram shows the gravity responses (labeled A, B, and C) to a body buried to depths A, B, and C, shown in the cross section in the lower half.
 
The amplitude of the gravity signal varies as a function of 1/depth<sup>2</sup> to the source. [[:file:applying-gravity-in-petroleum-exploration_fig15-5.png|Figure 2]] shows the gravity responses to a body of positive density contrast buried at different depths. The upper half of the diagram shows the gravity responses (labeled A, B, and C) to a body buried to depths A, B, and C, shown in the cross section in the lower half.
 
[[file:applying-gravity-in-petroleum-exploration_fig15-6.png|left|thumb|{{figure number|3}}]]
 
  
 
==Effect of size==
 
==Effect of size==

Revision as of 22:08, 21 January 2014

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
Store AAPG Store

Three key parameters of the source body affect the size and shape of the gravity response:

  • Density
  • Depth
  • Size

In the following discussion, 2-D cross sections demonstrate each of these parameters on theoretical gravity profiles. While the models may not be geologically reasonable, the concepts they demonstrate provide important building blocks for more complex geometric modeling, which is often performed to solve real exploration problems. When modeling gravity effects, it is much more important to constrain the size (shape) and depth of the geologic body than it is to constrain the density.

Effect of density

Figure 1 

The amplitude of a gravity anomaly has a linear relationship to density. Positive density contrasts produce gravity highs; negative density contrasts produce gravity lows. The wavelength of the anomaly is unaffected by differences in the density. Figure 1 shows the different gravity responses to a body with different positive density contrasts. In the upper half of the diagram are the gravity responses. The lower half of the diagram is a cross section. Values for the different densities are written next to the gravity response in the upper part of the figure.

Figure 2 
Figure 3 

Effect of depth

The amplitude of the gravity signal varies as a function of 1/depth2 to the source. Figure 2 shows the gravity responses to a body of positive density contrast buried at different depths. The upper half of the diagram shows the gravity responses (labeled A, B, and C) to a body buried to depths A, B, and C, shown in the cross section in the lower half.

Effect of size

The gravity response is related directly to the amount of anomalous mass. Size differences in three dimensions are X3 functions. file:applying-gravity-in-petroleum-exploration_fig15-6.png|Figure 3]] shows the gravity responses to bodies of the same density, at approximately the same depth, that are of different sizes.

See also

External links

find literature about
Gravity anomaly models
Datapages button.png GeoScienceWorld button.png OnePetro button.png Google button.png