Calculating Fault Gouge Ratio in EarthVision 5.1

From DGInsider Newsletter, Q2 2000

Figure 1

Figure 2

Figure 3

One of the exciting new developments for EarthVision 5.1 is the ability to calculate and display fault gouge ratio. Fault gouge ratio provides information about the sealing capacity of faults, and when combined with empirical data and Allan fault plane displays is a powerful tool for understanding and predicting fault seal. To calculate fault gouge ratio, you will need two things: first, a 3D property model of clay volume fraction (Vcl); and second, fault displacement information. The first is a property that can be gridded within EarthVision just like any other property; you can use minimum tension gridding or geostatistics. You must make sure to calculate this property for more than just the reservoir of interest.

The fault gouge calculation takes into account the composition of all layers that have moved past the layer of interest, so you must calculate Vcl not only in the reservoirs but also in any intervening shales. The second part of the input data (fault displacement) is automatically calculated when you do horizon gridding. If you have used the WorkFlow Manager, this information is saved in the projectname@_hg directory. If you use the Geologic Structure Builder, you need to save intermediate files.

Once you have the input data ready, bring up the fault gouge interface (Figure 1) by typing evfgr at the command line in an EarthVision window.

Fill in the sequence file name, the transform file (fault displacement), the Vcl property name, and the fault name. You may choose to calculate 2D grids and/or rgbs. (One of the side benefits of this calculation is that you can save the displacement grid for a fault surface as well as the fault gouge grid.) A typical grid of fault gouge ratio is shown in Figure 2.

Areas of seal or non-seal become even more apparent when this same information is shown in 3D (Figure 3). To produce this display, use the macro evmergefgr, which can be downloaded in a tar file (evmergefgr.tar) from our ftp site (ftp.dgi.com) in the directory pub/newsletter. This macro lets you superimpose fault gouge or displacement contours on one or more faults for which the 2D grids have been calculated.

 
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Last updated: March 22, 2007