Introduction to Electrokinetics - Electrokinetics for Petroleum and Environmental Engineers - page 11

which is valid, for example, for clays or clayey sands. Electrokinetic flow
rate increases with increasing clay content in sands. For sands it is possible
to raise the hydrodynamic component of the total flow by injection of spe-
cial purging solutions (Shapiro and Probstein, 1993).
Calculated k e /k can be used as an index for predicting the probability of
success and applicability of Electrically Enhanced Oil Recovery (EEOR).
The larger the ratio, the better the chance of success in dewatering sand
and increasing the relative permeability to oil. In very tight formations, k e
may exceed k causing an increase in the degree of electric dewatering at
the wellbore.
Electrical field application in situ, as a rule, leads to an increase in
temperature. In turn, the temperature increase reduces the viscosity of
hydrocarbon-containing fluids that, according to Eq. 1.9, would result in
an increase of the total flow rate (Chilingar et al., 1968). Analyzing the
results of “in situ” trials and verifying corresponding mathematical mod-
els, one should keep in mind this additional positive side effect to avoid
possible misinterpretations of electrokinetic efficiency. This effect is insig-
nificant for the dissolved gaseous hydrocarbons (like butane and meth-
ane). For crude oils (e.g., California crude oils), however, the viscosity can
be reduced more than twenty times by heating from 50 to 100 o C (Ungerer
et al., 1990). This (at least in theory) would increase the total fluids flow
twenty times.
Discussing an electrical field application for the acceleration of fluids
transport in situ, one needs to consider also electrical properties of soils
(electrical resistivity, for example) and ionization rate of the flowing fluids
that can considerably affect the total flow rate. In addition, Chilingar and
his associates (Chilingar et al., 1970) discovered that application of DC
field to some soils leads to an increase of their hydraulic permeability that,
in turn, can considerably accelerate the fluids transport. In addition, some
clays are destroyed (become amorphous) upon application of direct elec-
tric current, possibly as a result of driving the interlayer water out (do not
swell any longer).

1.5 Dewatering of Soils

Electrokinetics has long been applied in soil engineering. Several patents
on the removal of water from clayey and silty soils by electrokinetic were
issued in Germany before World War II. Later, the method was widely
and successfully used in Germany, England, the U.S.S.R., and Canada