1995-10-02_REVISION - M1977493 ‎(7)‎

• Permit No: M1977493
• IBM Index Class Name: Revision
• Doc Date: 10/2/1995
• Doc Name: Submittal
• From: Climax
• To: DMG
• Type & Sequence: TR8
• Media Type: D
• Archive: No

28
Physical Properties and Principles / Ch 2
oil, and water in multiphase flow systems makes the use of a fluid -free conductance
parameter attractive. When measured in m or cm k is very small, so petroleum
engineers have defined the darcy as a unit of permeability. If Eq. (2.28) is substituted
in Eq. (2.3), Darcy's law becomes
v — —kpgdh
p dl
(2.29)
Referring to this equation, 1 darcy is defined as the permeability that will lead to
I\ a specific discharge of I cm /s for a fluid with a viscosity of 1 cp under a hydraulic
gradient that makes the term pg dh /dl equal to 1 atm /cm. One darcy is approxi-
mately equal to 10 cm
In the water well industry, the unit gal /day /ft is widely used for hydraulic
conductivity. Its relevance is clearest when Darcy' w is couched in terms of Eq.
(2.4):
The early definitions provided .y e U . Geological Survey with regard to this
unit differentiate between a laboratory coefficient and a field coefficient. However,
a recent updating of these definitions (Lohman, 1972) has discarded this formal
differentiation. It is sufficient to note that differences in the temperature of measure-
ment between the field environment and the laboratory environment can influence
hydraulic conductivity values through the viscosity term in Eq. (2.28). The effect is
usually small, so correction factors are seldom introduced. It still makes good
sense to report whether hydraulic conductivity measurements have been carried
out in the laboratory or in the field, because the methods of measurement are very
different and the interpretations placed on the values may be dependent on the
type of measurement. However, this information is of practical rather than con-
ceptual importance.
Table 2.2 indicates the range of values of hydraulic conductivity and perme-
ability in five different systems of units for a wide range of geological materials.
The table is based in part on the data summarized in Davis' (1969) review. The
primary conclusion that can be drawn from the data is that hydraulic conductivity
varies over a very wide range. There are very few physical parameters that take on
values over 13 orders of magnitude. In practical terms, this property implies that
an order -of- magnitude knowledge of hydraulic conductivity can be very useful.
Conversely, the third decimal place in a reported conductivity value probably has
little significance.
Table 2.3 provides a set of conversion factors for the various common units
of k and K. As an example of its use, note that a k value in cm can be converted to
one in ft by multiplying by 1.08 x 10 -3 . For the reverse conversion from ft to
cm multiply by 9.29 x 10
I I
C
0 0
N
Q , O
E�
_
Y
L
a C
C
o C
U C
0 E
C
of
LL
cm
ft 9.25
darcy 9.8",
mis 1.0:
ft /s 3.11
U.S. gal /day /ft =5.4:
*To obtain k i