Page 213 - Petrophysics

186 PETROPHYSICS: RESERVOIR ROCK PROPERTIES

1000

- 100
h
U
5
2
m
n
4 10 ...

1
0.1 I 10 I00
Time, hrs

Figure 3.58. Longlogplot of AP and t*AP' versus test time,

probability of the presence of reservoir nog-uniformities of a certain type
in any reservoir by considering the cores, logs, and general geologic
background of the reservoir [47]. Using a statistical analysis of laboratory
measurements of air permeability in eight directions spaced at 45"
intervals on 142 two-inch vertical plugs from 30 cores, Greenkorn et al.
showed that there is significant point anisotropy in about 60% of the core
plugs [53]. Also, they found that the permeability of a heterogeneous
anisotropic porous medium is a tensor consisting of a point-to-point
variation that depends on grain size and a point variation that depends on
bedding. Trudgen and Hoffmann proposed a procedure which employs
Pearson's system of curve fitting for defining a frequency distribution
of reservoir rock properties obtained from core data [ 541. Many more
statistical methods for describing various reservoir rock properties were
proposed. However, only few of these methods were found to be
practical.
Testerman described a statistical technique for identifying and describ-
ing porous and permeable zones in a reservoir, and for determining
which ones are likely to be continuous between adjacent wells
[55]. The technique is particularly useful in describing permeability
distribution in a reservoir where crossflow between adjacent communi-
cating reservoir strata, due to imbibition and gravity segregation, is
important. Inasmuch as there are, however, no geological parameters
concerning the depositional environment in the statistical evaluation,
judgment is necessary to determine whether the zones so defined
are, in fact, continuous and consistent with the geological model.