WELLOG                          SIMANDOUX

Revised 7-26-2007

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SIMANDOUX EQUATION:

The Simandoux equation for water saturation is as follows:

                        Sw = -Vsh/Rsh + ((Vsh/Rsh)² + 4Fe^m/a Rw (1-Vsh) Rt)^1/2/(2Fe^m/a Rw (1-Vsh)

Where:

Fe = FN – FNm (1-Vsh) – Vsh (FN)sh + (DFN)ex/(Sxo (FN)mf + (1-Sxo) (FN)h – (FN)m)

FN = Neutron log apparent porosity

(FN)mf = Correction for invaded filtrate = ((rmf (1-p))

(FN)h = Correction for formation hydrocarbons = 9 ((4–2.5 rh)/(16-2.5 rh) rh

(DFN)ex = Excavation effect = 2FN² (1-Sxo) (1-(FN)h) (1-(1-Sxo) (1-(FN)h))

rmf = Density of mud filtrate

P = Dissolved solids content of mud filtrate (ppm x 10⁶)

rh = Density of formation hydrocarbons

Sxo = Estimated filtrate saturation in the flushed zone

Fe = Effective shale corrected porosity

Vsh = Shale content

(FN)sh = Neutron response to shale porosity

(FN)m – Correction for departure of formation lithology from the value used in logging

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