Introduction to Electrokinetics - Electrokinetics for Petroleum and Environmental Engineers - page 19

( )

2 2

injected is equal to the pore volume invaded [ qt ], the radial

distance the acid will penetrate until being spent, r a (ft), is equal to:

= pf h r − r

i a w

0 0936 . qt

h

2

(1.12) r =

i

+ r

a w

pf

where q i is the acid injection rate (bbl/min); t is the spending time (sec);
ϕ is the fractional porosity; h is the formation thickness (ft); and r w is the
wellbore radius (ft).
As shown in Eq. (1.12), in order to increase r a , either t or q i should be
increased. The injection rate q i , can be increased considerably by the appli-
cation of DC current (see Chilingar et al., 1968, 1970, for example). The
application of electrokinetics in Abu Dhabi carbonate reservoir rocks has
been proven to be very promising by Haroun et al. (2009).
As shown in Fig. 1.7, using electrokinetics, it is necessary to deploy an
anode in the well adjacent to the formation being acidized, and a nearby
cathode either at the surface or in the adjoining well. The electrokinetic
flow will occur from the anode towards the cathode, and thereby acidizing
the target formation, enabling the acid to move faster and deeper into the
formation in a guided fashion (see Wittle et al., 2008). The two electrodes
(anode and cathode) must be connected by cables to the Direct Current

e -

D.C.

Acid

Buried
cathode (.)

Casing

Tubing

Electric current (D.C.)

D.C. e -

Aluminum
anode (+)

Figure 1-7 Electrodes arrangement for acidizing operation (after Chilingar et al., 2013).