Formation Evaluation Through Casing - Cased-Hole Log Analysis and Reservoir Performance Monitoring - page 160

Table 11.3 ʣ values for log
interpretation

ʣ Material Sigma (Cu)

Matrix Sand 8-10

Limestone 12

Dolomite 8

Hydrocarbon Oil (function of R s ) 22

Gas (function of ʳ g , P , T ) 8

Water Fresh 23

Seawater 34

Brine 122

Figure 11.21 shows this method. Note that all water-bearing points fall on the
line joining the matrix (porosity = 0, ʣ = 10) to the water (porosity = 100, ʣ = 100).
Likewise, all 100 % oil-bearing points lie on the line joining the matrix to the oil
(porosity = 100, ʣ = 22). Thus, all points lie inside a solution triangle covered by the
matrix, water, and oil points. By simple constructions, lines of constant S w can be
drawn. The dashed lines on Fig. 11.21 join at the point given in Question #11.3,
( ˕ = 30 %, ʣ Log = 25.3).

Fig. 11.21 Interpretation in clean formations

How much confidence can be placed in the value of S w derived as in Fig. 11.21 ?
To a large extent, the accuracy depends on the difference between ʣ hy and ʣ w . In
fresh formation waters (low ʣ w ), the interpretation will be very questionable; but in
very salty formation waters (high S w ), it will be reliable. Figure 11.22 illustrates
this concept.