Formation Evaluation Through Casing - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 159

Hydrocarbon Σ hy φ (1− S w )

φ

φ S w

Water Σ w

Matrix Σ ma

(1−φ)

Fig. 11.20 Components of ʣ Log

Of course, the “fluid” may, in fact, be a mixture of oil and water, in which case,
the log response is described by:

( ) + ( )

SSfSfSf
Log

= 1 - S + 1 S -.

ma w w hy w

By rearrangement of the equation, we have:

( ) - ( )

SSfS S - -

Log a hy a

S w =

( )

fS S -

w hy

Question #11.3
Given: ʣ Log = 25.3 cu.
ʣ ma = 10.0 cu.
ʣ hy = 22 cu.
ʣ w = 100 cu.
˕ = 30 %.
Find S w = _________________ .

In the previous example, the values for ʣ ma , ʣ log , and ʣ w were given. However, in
practice, these values may not be known. As a guide, Table 11.3 gives values of ʣ
for commonly found materials. More exact methods for inding ʣ ma , ʣ w , and ʣ hy will
be covered later in the text.
Log interpretation in clean formations is straightforward. The linear equations
can also be thought of graphically. If, for example, a crossplot is made of ʣ (on the
Y -axis) and ˕ , (on the X -axis), straight lines represent mixtures of pairs of
components.