GATE-2018 (24) :Wyllie – Time average equation

CSIR-NET JUNE 2018

101) The Formation factor obtained for the data given below is

Resistivity of the flushed zone=1.30Ωm

Resistivity of the mud filtrate=0.65Ωm

Residual oil saturation=25%

Saturation exponent = 2

a)0.125 

b)1.125 

c)2.125 

d)3.125

(Thanks to Suresh Sir ANU)

(Thanks to Neeraja AU)

Sol:

The relation between Resistivity of the flushed zone, Resistivity of the mud filtrate, Water Saturation and Formation factor is.

$S_w^n=\frac{FR_{mf}}{R{xo}}-(1)$

n=2

Above problem Residual oil saturation is given, using this we can calculate the Water Saturation using below formula.

$S_w=1-S_h$

$S_w=1-0.25$

$S_w=75%$

$S_w=0.75$

$S_w^2=\frac{FR_{mf}}{R{xo}}$

$FR_{mf}=S_w^2R_{xo}$

$F=\frac{S_w^2R_{xo}}{R_{mf}}$

$F=\frac{(0.75)^2\times1.30}{0.65}=\frac{0.7312}{0.65}=1.125$

Formation Factor  (F)=1.125