Typical Fault Seal Potential Variable settings

This section describes typical settings required in WizGen in Flexible project mode to calculate the most commonly used measures of Fault Seal Potential, i.e. Shale Gouge Ratio, Clay Smear Potential as per Yielding et al. or as per Fulljames et al., Shale Smear Factor as per Lindsay or by combining multiple shale beds.

The user can also create their own method, for example see the modified version of calculating Clay Smear Potential created using user-defined keywords in the CELLPROP plugin.

Shale Gouge Ratio (SGR)

SGR is defined as:-

Equation constants

Therefore, in the generalised FSP equation, Exponent l = -1, Exponent m = 1, Exponent n = 0 and Exponent p = 1.

Distance options

Distance is not used in the equation (since Exponent n = 0), however a valid distance option is still required. Distance option, Centre of beds (distance_switch = 2) is as good as any.

Combination options

If the properties of the cells in the footwall and hangingwall are the same, any of the Combination options - Maximum of layers then sum, Sum layers then maximum, Sum layers then take average, Sum in hangingwall or Sum in footwall would give sensible answers. The option Sum layers then take average is equivalent to the default in TransGen version 2, and is, in general, our recommended combine option for SGR. Sum in hangingwall is recommended for growth faults or in reservoirs with severely eroded crests.

Effective vshale

This setting will depend on the Included Data for the current project. If, as in the TRIANGLE demo dataset, there is only NTG data, the Net-to-gross only option would be applicable.

Plunge correction

Retain the default Three dimensional setting unless you specifically want to report the FSP measures on a vertical projection of the fault.

Shale definition

If, as in the TRIANGLE demo dataset, all the cells have a non-zero Vshale, all cells must be used in the calculation. Shale definition is therefore set to Based on all cells.


The WizGen Fault Seal Potential Variables page looks like this:-

and the TGFSP keyword record in the TGDATA run file is:-

'sgr' -1 1 0 1 4 ' ' 1 6 1 ' ' 1 /

where the string is:-
'name' l m n p shale_switch shale_ string distance_switch combine_switch evshale_switch evshale_string plunge_correction /

Clay Smear Potential (CSP) after Yielding et al. 1997

CSP is defined as:-

Equation constants

Therefore, in the generalised FSP equation, Exponent l = 0, Exponent m = 2, Exponent n = -1 and Exponent p = 0.

Distance options

Centre of beds (distance_switch = 2) setting is appropriate.

Combination options

The summation is performed on the maximum values of the terms calculated in the footwall and hangingwall, i.e. Maximum from layers then sum.

Effective vshale

This setting will depend on the Included Data for the current project. If, as in the TRIANGLE demo dataset, there is only NTG data, the Net-to-gross only option would be applicable.

Plunge correction

Retain the default Three dimensional setting unless you specifically want to report the FSP measures on a vertical projection of the fault.

Shale definition

When using the Maximum from layers then sum combination option, the only possible Shale definition to individually name the Layers.


The WizGen Fault Seal Potential Variables page looks like this:-

and the TGFSP keyword record in the TGDATA run file is:-

'csp_yielding' 0 2 -1 0 1 '8-13, 26-29, 34, 38, 45-47' 1 1 1 ' ' 1 /

where the string is:-
'name' l m n p shale_switch shale_ string distance_switch combine_switch evshale_switch evshale_string plunge_correction /

Clay Smear Potential (CSP) after Fulljames et al. 1997

The Fulljames et al. (1997) definition differs from that of Yielding et al. in that:-

Distances are measured to the Far side of beds.

FSP is calculated independently in the hangingwall and footwall sides of the fault and the final FSP is the maximum of these, i.e. Combination options setting should be Sum layers then take maximum.

NOTE:- It is possible with this method of CSP calculation to base the Shale definition on any of the options, but for direct comparison with the CSPs obtained as per Yielding et al., the Layers setting has been retained.


The WizGen Fault Seal Potential Variables page looks like this:-

and the TGFSP keyword record in the TGDATA run file is:-

'csp_fulljames' 0 2 -1 0 1 '8-13, 26-29, 34, 38, 45-47' 2 2 1 ' ' 1 /

where the string is:-
'name' l m n p shale_switch shale_ string distance_switch combine_switch evshale_switch evshale_string plunge_correction /

Shale Smear Factor (SSF) after Lindsay et al. 1993

The original SSF formulation (Lindsay et al. 1993) is:-

This method does not consider the possibility of multiple shales, calculating the SSF value associated with every shale that has passed a point on a fault and taking the minimum. Unlike both SGR and CSP, faults with lower value of SSF are more likely to have higher sealing capacity.

Equation constants

Therefore, in the generalised FSP equation, Exponent l = 1, Exponent m = -1, Exponent n = 0 and Exponent p = 0.

Distance options

Distance is not used in the equation (since Exponent n = 0), however a valid distance option is still required. Distance option, Centre of beds (distance_switch = 2) is as good as any.

Combination options

The formulation of SSF attributed to Lindsay et al. calculates the SSF value associated with every shale that has passed a point on a fault and takes the minimum, so the Combination options should be set to the Minimum value.

NOTE:- More connections will be undefined using SSF as a FSP measure than when using either of the CSP methods. This is because any connections which have not had any shales layers pass them are undefined for SSF because the Minimum value combination option setting does not involve summation and it is impossible to define the minimum term of no terms at all. Whereas all the CSP measures involve some sort of summation and the sum of no terms is 0.0.

Effective vshale

This setting will depend on the Included Data for the current project. If, as in the TRIANGLE demo dataset, there is only NTG data, the Net-to-gross only option would be applicable.

Plunge correction

Retain the default Three dimensional setting unless you specifically want to report the FSP measures on a vertical projection of the fault.

Shale definition

This should be set to Effective Vshale cutoff and input an appropriate value, e.g. 0.5 to define the shale layers based on the Effective vshale (which is a simple function of Net-to-gross).


The WizGen Fault Seal Potential Variables page looks like this:-

and the TGFSP keyword record in the TGDATA run file is:-

'ssf_lindsay' 1 -1 0 0 2 '0.5' 2 4 1 ' ' 1 /

where the string is:-
'name' l m n p shale_switch shale_ string distance_switch combine_switch evshale_switch evshale_string plunge_correction /

Shale Smear Factor (SSF) Definition 2

This SSF combines multiple shale beds using the expression:-

This expression cannot be calculated directly using the generalized expression for FSP and this is a rare example of when it is useful to modify a FSP in the PERM or THICK plugin.

The Fault Seal Potential Variables are set to calculate the summed Shale bed thicknesses which are then used in either the permeability or thickness plugin to get the expression for SSF.

Equation constants

To calculate the summed shale bed thicknesses in the generalised FSP equation, Exponent l = 0, Exponent m = 1, Exponent n = 0 and Exponent p = 0.

Distance options

Distance is not used in the equation (since Exponent n = 0), however a valid distance option is still required. Distance option, Centre of beds (distance_switch = 2) is as good as any.

Combination options

This is set to Sum layers then take average to calculate shale bed thickness from the average of the thickness in the footwall and thickness in the hangingwall.

Effective vshale

This setting will depend on the Included Data for the current project. If, as in the TRIANGLE demo dataset, there is only NTG data, the Net-to-gross only option would be applicable.

Plunge correction

Retain the default Three dimensional setting unless you specifically want to report the FSP measures on a vertical projection of the fault.

Shale definition

This should be set to Effective Vshale cutoff and input an appropriate value, e.g. 0.5 to define the shale layers based on the Effective vshale (which is a simple function of Net-to-gross).


The WizGen Fault Seal Potential Variables page looks like this:-

and the TGFSP keyword record in the TGDATA run file is:-

'ssf_2' 0 1 0 0 2 '0.5' 1 6 1 ' ' 1 /

where the string is:-
'name' l m n p shale_switch shale_ string distance_switch combine_switch evshale_switch evshale_string plunge_correction /

The THICK (or PERM) plugin is then used to modify the summed shale bed thickness to derive an expression for SSF as shown below in the User-defined plugins page of WizGen.

The if statement is needed to ensure that connections which have had no shales pass them are set to undefined connections, otherwise they would take on values of infinity.