Environmental Engineering Reference
In-Depth Information
Then, the core was transferred to the EK test cell. In the EK cell the glass
frits separated the core compartment from the formation water in the elec-
trode reservoirs, and the electric field was applied using titanium mesh
electrodes placed at the two-end caps of the core.
The typical current densities used in field applications of EKEOR have
been reported to be in the range of 1.0-1.5 Amp/m
2
(Wittle et al., 2008a
and 2008b). A constant voltage gradient of 4V/cm was applied to the
cores in order to achieve current density of 1 Amp/m
2
in the laboratory
experiments. The volume production of each liquid was monitored at the
cathode reservoir over time for 36 hours. Knowing the measured volume
of the produced water, the applied electrical gradient, and the absolute
EO permeability of the core (
k
e
), the
k
er w
,
coefficient could be computed
at a specific initial water saturation of the core. For each measurement,
the core was dried and air vacuumed and the flooding procedure was
repeated to establish the next water saturation level for evaluation of the
corresponding
k
er ww
,
coefficient. Figure 5.5 shows the measured
k
er w
,
coefficient variation at four different water saturations of the four rock
cores designated as A, B, C, and D. As observed, the
k
er w
,
coefficients
increased with water saturation, owing to higher water production by the
EO flow.
5.8.4.2
Diagonal relative permeability coefficient for
oil phase
[
k
er oo
Most crude oils are mixtures of non-polar compounds. Hence unlike water,
which is polar and may contain dissolved charged particles, direct appli-
cation of electric field does not create a notable EO body force in crude
oil. To better discern the effect of applied electric field on the oil phase
compared to the water phase, the EO permeability of the porous medium
is computed using water only and the oil only as the pore fluid. Using
Helmholtz-Smoluchowski equation, the computed ratio of
k
e
(cm
2
/V.sec)
of a given formation with oil to that with water is significantly low, rang-
ing between10
-7
to 10
-3
. This stems from the large differences between the
dynamic viscosity and the permittivity of the two liquids. The dynamic
viscosity of most crude oils is in the range of 0.038-0.339 Pas.sec (for heavy
crude oils the range is 1-5 Pas.sec), while for water it is around 0.001Pas.sec.
The range of relative permittivity of most oils is 2.5-5, while for water it is
80. In conclusion, the
k
er,oo
was set equal to zero assuming negligible effect
of the applied electrical gradient on the oil phase body force (Ghazanfari,
2013a).
]
,
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