Net Pay

This section is about some methods to estimate some reservoir properties, such as net pay, based on siliciclastic well log data, and also a manual method using cutoffs.

Basic Calculations

stoneforge.reservoir.net_pay.cutoff(log, t, lower=True, fillzeros=False, equal=False)

Applies a cutoff to a well log data based on a specified threshold value (Crain[1], Nery[2]).

Parameters:

• log (array_like) – The well log data to which the cutoff will be applied.

• t (float) – The threshold value for the cutoff.

• lower (bool, optional) – Whether to apply the cutoff on lower values (True) or higher values (False). Default is True.

• fillzeros (bool, optional) – If True, values that do not meet the cutoff condition will be filled with zeros. If False, they will be filled with NaN. Default is False.

• equal (bool, optional) – Whether to include values equal to the threshold in the cutoff condition. Default is False.

Returns:

An array where values that meet the cutoff condition are set to 1.0, and values that do not meet the condition are set to 0.0 or NaN based on the fillzeros parameter.

Return type:

array_like

Notes

The function applies a cutoff to the input log data based on the specified threshold value t. The cutoff is applied either to values below or above the threshold, depending on the lower parameter. If equal is True, values equal to the threshold are included in the cutoff condition. If fillzeros is True, values that do not meet the cutoff condition are filled with zeros; otherwise, they are filled with NaN.

stoneforge.reservoir.net_pay.net_pay_siliciclastic(vsh, phi, sw, vsh_t=0.3, phi_t=0.2, sw_t=0.3, fillzeros=False)

Calculates the net pay for siliciclastic reservoirs based on shale volume, porosity, and water saturation logs (Crain[1], Nery[2]).

Parameters:

• vsh (array_like) – Shaliness log data (dimensionless).

• phi (array_like) – Porosity log data (dimensionless).

• sw (array_like) – Water saturation log data (dimensionless).

• vsh_t (float, optional) – Shaliness threshold value. Default is 0.3.

• phi_t (float, optional) – Porosity threshold value. Default is 0.20.

• sw_t (float, optional) – Water saturation threshold value. Default is 0.3.

• fillzeros (bool, optional) – If True, values that do not meet the cutoff conditions will be filled with zeros. If

Returns:

A dictionary containing the following keys: - ‘rock’: An array indicating the rock presence based on the shaliness threshold. - ‘res’: An array indicating the reservoir presence based on the porosity threshold and rock presence. - ‘pay’: An array indicating the pay zone based on the water saturation threshold and reservoir presence.

Return type:

dict

References

[1] (1,2)

E. R. (Ross) Crain. Crain’s petrophysical handbook. 1999. Accessed: 2026-02-23. URL: https://spec2000.net/index.htm.

[2] (1,2)

G. G. Nery. Perfilagem Geofísica em Poço Aberto: Fundamentos básicos com ênfase em petróleo. SBGF, 2013. URL: https://sbgf.org.br/mysbgf/livros/perfilagem.php.