Page 161 - Percolation Models for Transport in Porous Media With

158 CHAPTER 9 ELECTRJC ACTION EFFECT. EXPERiMENT

Table 9.1:

Portion of Fraction in
Grain Size, mm Total Mass of Specimen,%
I II
2.5 0.04 0.02
1.25 0.13 0.20
0.63 1.85 3.15
0.315 31.88 24.04
0.16 44.34 36.57
< 0.16 21.78 36.02

However, since during the fluid flow, clay accumulates in the thin capillaries, it
follows that the fraction K- of the mudded out capillaries is small. This effect sin
1
the low conductivity.
At first, vertical tubes were packed with the rock, with distilled water supplied
gradually from the bottom sides of the tubes. This direction of water upplying en-
abled to achieve the maximal displacement of the air from the rock pores, uniform
packing and saturation of the rock with the fluid. Three tubes were usually used.
Electric treatment with impulse current was carried out in the first tube; electric
treatment with alternating current, in the second; and the third one was left for
reference. The volume of water used for the saturation of the rock in tubes was
measured, and the porosity was determined to equal 18 to 23 % in this series of
experiments.
After the tubes have been packed, the flow of distilled water through their
cross-section was set up for 15 to 25 days, until the production rates of the tubes
steadied. Further, the electric treatment of the rock with alternating current was
carried out, with simultaneous measurements of its production rate and electric
conductivity taken.
High resistance of the rock did not permit to achieve large values of the current
density even for large values of the electric field intensity.
The experiments showed that the electric conductivity of the rock bears a
notable dependence on the intensity of the applied electric field. Its permeability
increases reversibly by 30- 40% for Eo V /m, and three-fold for 3E 0 V /m. After
the current was switched off for 5 - 10 minutes, the permeability fell to its original
value. In other words, for small current density, in spite of the large values of field
intensity, no irreversible changes to the permeability were observed. This confirms
the temperature-related nature of the causes for the irreversible changes, which
were discussed in chapter 8. Substantial reversible changes in the permeability