Читать книгу Acoustic and Vibrational Enhanced Oil Recovery - George V. Chilingar - Страница 16

Electric currents are prevalent in the Earth’s crust and probably were amplified in the geologic past (Serruya et al., 1967 [29]). Upon application of DC current, for example, the flow rate can increase many fold both in clays and sands (Amba et al., 1965 [1]; Chilingar et al., 1970 [10]). Thus, the presence of intense electric currents in the geologic past possibly facilitated primary migration of oil. Figure 1.2 shows the schematic diagram of electrokinetic double layer.

Figure 1.2 Schematic diagram of electrokinetic double layer (I: Immobile layer, II: Mobile double layer, III: Free water, IV: Velocity profile as envisioned by Dr. G. V. Chilingar. Solid curved line: velocity profile in a capillary. P-D.C., current power supply).

Theory of the electrokinetic flow is based on a double-layer theory as illustrated in Figure 1.2. According to Figure 1.2, the negatively charged surface of the clays attracts the positive ions of the aqueous medium, forming the immobile double layer. This immobile double layer is followed by a thick mobile layer with a predominance of positively charged ions (cations) with a few negatively charged ions (anions).

Upon application of direct electric current, the mobile double-layer moves toward the cathode, dragging the free water. A schematic diagram of EEOR field setup, as used by Wittle et al. (2008) [38] and (2011) [39] in Canada and California oil fields, is presented in Figure 1.3.

In case where imposed electric potential gradient, E, is in the same direction as the pressure drop (Δp), the total flow rate (q_t) upon application of D.C. current is as follows:

(1.1)

where k is the hydrodynamic permeability; is the electrokinetic permeability; Δp is the pressure drop; µ is the viscosity; L is the length of porous media; A is the cross sectional area of porous media; ζ is the zeta potential; F is the formation resistivity factor (Archie’s); E is the electrical potential; and D is the dielectric constant.

Figure 1.3 Schematic diagram of EEOR (Electrical Enhanced Oil Recovery) electrode arrangement in oil fields as used by Wittle et al. (2008) [38] and (2011) [39], Ambah et al. (1965) [1], and Titus et al. (1985) [35].

Equation (1.1) can be presented in a dimensionless form by normalizing the flow rates and, thus, eliminating µ, A, and L terms (Chilingar et al., 1970 [10]):

(1.2)

and

(1.3)

where q_i is the initial hydrodynamic stabilized flow rate:

(1.4)

Thus, the possible existence of strong D.C. current in the rocks during the geologic past could have facilitated the movement of fluids (Ambah et al., 1965 [1]).