Environmental Engineering Reference
In-Depth Information
where
V
i
is the total volume of phase
i
,
V
p
is the pore volume. In the sec-
ond equation,
is the porosity and
V
T
is the total volume of the rock.
The simplest model for two phase fl ow is to assume that brine
and CO
2
fl ow completely independently. Suppose in our rock we have
S
g
φ
0.1, i.e., 10% of the pore volume is occupied by CO
2
and 90% by
brine. If the fl ow can be seen as two independent single fl ows, we have
10% of the rock in which CO
2
permeates as if it were a single phase and
in 90% of the rock, single phase fl ow of brine. Or, in more general
terms, if
S
i
is the saturation of phase
i
, we have a relative permeability,
simply given by:
=
k
=
S
ri
,
i
For most fl uids
k
r,i
is smaller than 1. Let us now see how differences
in wettability of the two phases change this simple picture of two-phase
fl ow.
We consider the two phase fl ow of brine and CO
2
. As we have seen
before, brine is the wetting phase.
Figure 9.7.1
presents two scenarios
for a high (a) and low (b) brine saturation. In
Figure 9.7.1
(a)
, the brine
phase occupies most of the pore space, and thereby forms a connected
Figure 9.7.1
Connected phase in pores
(a) Groundwater forms the connected phase and is relatively mobile while CO
2
exists
only as discrete blobs.
(b) CO
2
forms the connected phase while water coats the grains.
Search WWH ::
Custom Search