Page 237 - Fundamentals of Enhanced Oil and Gas Recovery

Waterflooding 225

It has been observed from many field projects that the level of improved oil recov-
ery from alkaline flooding is low. Based on analysis of the data reported by Mayer
et al. [65], the incremental oil recovery factor over waterflooding was 1% 2% in most
of the projects, and 5% 6% in a few projects [45].

7.6.2.4 Multicomponent Ion Exchange
Different affinities of ions on rock surfaces results in the Multicomponent Ion
2+ 2+
Exchange (MIE) in which multivalent or divalent such as Ca and Mg strongly
adsorbed on rock surfaces until the saturation point of the rock. Polar compounds
present in the oil phase and multivalent cations at clay surfaces bonded together
and form organometallic complexes; this mechanism yields the rock surface
toward oil-wet condition. During the injection of LS brine, MIE will take place,
removing organic polar compounds and organometallic complexes from the
surface and replacing them with uncomplexed cations [45,66].The suggested
mechanism of MIE is supported by the pore-scale model proposed by Sorbie and
Collins [66].
Meyers and Salter [67] carried out several adsorption experiments; in their tests,
they observed that the steady-state effluent concentrations of calcium and magne-
sium were observed to be slightly greater than the injected concentrations. These
excess concentrations increased as the injection concentrations decreased. When
NaCl brine was injected into the cores, “residual” calcium and magnesium concen-
trations were still observed in the effluent. However, Valocchi et al. [68] injected
21
fresh water in a brackish water aquifer and noticed that the concentration of Ca
21
and Mg in different control wells were lower than the invading water and the
connate brine [45].

7.6.2.5 Double Layer Effect
The double layer theory combines the effects of the electrostatic repulsion and van
der Waals attraction owing to the so-called double layer of counter ions. LS brine
using the mechanism of the expansion of the electric double layer to reduce
clay clay attraction. Indirect interactions between oil, brine, and rock highly
affect the discharge of clay particles; this mechanism normally occurs in kaolinite
plates and involve in their charge distribution [46]. LS water makes water film
more stable owing to this expanded double layer effect, resulting in more water-
wet on clay surfaces and more oil is detached; conversely, adsorption of divalent at
water/sand and water/oil interfaces changes the wettability from water-wet state
to oil-wet condition [45,70,71].