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

GATE-2008

69. In electrical logging, the measured resistivity of flushed zone is 19.2 Ωm, the resistivity of mud filtrate is 1.33 Ωm and the computed value of residual oil saturation in flushed zone is 20%. The value of formation resistivity factor is

A) 8.50                    

B)8.85                          

C)9.11                    

D)9.24

Solution:

The residual water saturation (S_wr) = ?

Formation factor (F) = ?

Resistivity of flushed zone (R_xo)= 19.2 Ωm
 

Resistivity of mud filtrate (R_mf) = 1.33 Ωm

Residual oil saturation (S_or) = 20%

                                  = 20 / 100 

 

                                  =0.2

S_wr = 1- S_or

      = 1- 0.2

      = 0.8

Formula: 

 

(S_wr)² = (F * R_mf) / R_xo ---------------------(1)

F= ((S_wr)² * R_xo )/ R_mf

F= (0.8)² * 19.2 / 1.33

F= 0.64 * 19.2 / 1.33

F= 9.239

Formation factor (F) = 9.24