Page 311 - Petrophysics 2E

282 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

TABLE 4.17
COMPARISON OF WATER SATURATIONS AND OIL VOLUMES CALCULATED
FOR NORMALLY DRIED AND HUMIDITY-DRIED CORES [32]

Humidity-dried Core
(145°F and 45%-Relative Humidity)
Oven-dried Core
Variable (1 8O"-24O0F) (1) (2)
Porosity (%) 20 17.7 17.7
Grain density, (g/cm3) 2.65 2.61 2.61
CEC (meq/lOOg) 7 7 7
m 1.63 1.63 1.51
a 1 1 1
f 13.78 16.82 13.66
n 2.38 2.38 1.91
m* 1.92 1.92 1.9
a* 1 1 1
p" 21.9 21.9 26.84
n* 2.87 2.87 2.51
Rt 20 20 20
Qv 0.74 0.85 0.85
Rv @ 95°F 0.5 0.5 0.5
B 3 3 3
s, 0.55 0.58 0.52
(1-SW) (7,758) 698 577 659
@ (17% low) (5.6% low)
(1) Humiditydried porosity and grain density used with electrical properties data calculated on
basis of ovendried core porosity.
(2) Humiditydried porosity and grain density used with electrical properties data calculated on
the basis of humidity-dried porosity.

These results clearly show that partially dried core data yield erroneously
low oil-in-place values and, therefore, it is recommended that this type
of data should not be used in the Waxman and Smits equations [28].
Some clay-bearing cores crack when totally dried in an oven at high
temperatures and, consequently, data measured in these cores are totally
non-representative of reservoir conditions. In this case, laboratory tests
should be made on partially dried core samples for determining porosity,
grain density, and electrical properties. Water saturation and oil-in-place
are calculated as in Column 3 of Table 4.17. The calculated oil-in-place
in the Shannon sand [659 bbl/acre-ft, Column 31 is 5.6% lower than that
obtained from the totally oven-dried cores [698 bbl/acre-ft, Column 11.
Thus, it is important that the testing laboratory indicates in the report
whether saturation data are based on the partially (humidity) or totally
(oven)-dried cores. Both partially and totally dried core data including