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Line 33: − − − http://archives.datapages.com/data/bulletns/1997/06jun/0897/Images/Fig03.GIF − − Figure 3-Gouge ratio algorithms for estimating likelihood of clay entrainment in the fault gouge zone. The gouge ratio reflects the proportion of the sealing lithology in the rock interval that has slipped past a given point on the fault. (a) Calculation for explicit shale/clay beds in an otherwise shale-free sequence; Dz is the thickness of each shale bed. (b) Calculation for a sequence of reservoir zones; Dz is the thickness of each reservoir zone and Vcl is the clay volume fraction in the zone.
Fault seal quantitative prediction: shale smear factor, shale gouge ratio, and smear gouge ratio (view source)
Revision as of 21:25, 29 September 2014
, 21:25, 29 September 2014→Shale gouge ratio (SGR)
==Shale gouge ratio (SGR)==
==Shale gouge ratio (SGR)==
The shale gouge ratio is simply the percentage of shale or clay in the slipped interval. Figure 3a illustrates how this would be calculated, at a given point on a fault surface, for explicit shale beds
[[File:Shale-gouge-ratio-fig3.png|thumb|300px|{{figure number|3}}Gouge ratio algorithms for estimating likelihood of clay entrainment in the fault gouge zone. The gouge ratio reflects the proportion of the sealing lithology in the rock interval that has slipped past a given point on the fault. (a) Calculation for explicit shale/clay beds in an otherwise shale-free sequence; Dz is the thickness of each shale bed. (b) Calculation for a sequence of reservoir zones; Dz is the thickness of each reservoir zone and Vcl is the clay volume fraction in the zone.]]
(4) SGR = (Σ (shale bed thickness) /fault throw))/fault throw ×100%
The shale gouge ratio is simply the percentage of shale or clay in the slipped interval. [[:File:Shale-gouge-ratio-fig3.png|Figure 3a]] illustrates how this would be calculated, at a given point on a fault surface, for explicit shale beds (Equation 4):
<math>\text{SGR} = \frac{\Sigma (\text{shale bed thickness})}{\text{fault throw}} \times 100%</math>
The shale thicknesses are measured in a "window" with a height equal to the throw; therefore, this window represents the column of rock that has slid past this point on the fault. The definition can be extended for cases where the stratigraphic breakdown is by reservoir zone rather than by individual beds. In these cases, the net contribution of fine-grained material from each reservoir zone can be related to the clay content and thickness of the zone. The corresponding equation is (see Figure 3b)
The shale thicknesses are measured in a "window" with a height equal to the throw; therefore, this window represents the column of rock that has slid past this point on the fault. The definition can be extended for cases where the stratigraphic breakdown is by reservoir zone rather than by individual beds. In these cases, the net contribution of fine-grained material from each reservoir zone can be related to the clay content and thickness of the zone. The corresponding equation is (see Figure 3b)
The gouge ratio algorithm can be extended to include other lithologies in addition to shale/clay. For example, if numerous coal beds are present they may contribute to the fine-grained fault gouge, although less efficiently than smeared clay. In this case the coal units can be included in the summation and down-weighted with respect to the shale.
The gouge ratio algorithm can be extended to include other lithologies in addition to shale/clay. For example, if numerous coal beds are present they may contribute to the fine-grained fault gouge, although less efficiently than smeared clay. In this case the coal units can be included in the summation and down-weighted with respect to the shale.
Unfortunately both shale gouge ratio and smear gouge ratio are commonly called SGR. They are inversely related.
Unfortunately both shale gouge ratio and smear gouge ratio are commonly called SGR. They are inversely related.
==Smear gouge ratio (SGR)==
==Smear gouge ratio (SGR)==