Page 15 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 1 History of Low-Salinity and Smart Waterflood 7

drop. These observations imply the ability of CaCl 2 on the adsorption of organic material than a gradient in
brine to change reservoir wettability toward more the salinity. In coreflooding tests, production, salinity,
oil-wet. Experiments using Middle Eastern sandstone and effluent pH are monitored. The experimental
cores are carried out to review the observations by results indicate that LSWF causes a local increase in
Lager et al. (2008) and reveal the main factor for pH and the pH increases result in the desorption of
LSWF. The core saturated with oil is flushed by forma- organic components of crude oil from the clay. Based
tion brine. The formation brine having TDS with on the results, the salting-in mechanism is proposed
þ
238,000 mg/L is composed of Na with 84,300 mg/L, for LSWF. Another study by RezaeiDoust, Puntervold,
Ca 2þ with 6800 mg/L, and Mg 2þ with 1215 mg/L. The and Austad (2011) carried out further experiments to
pure NaCl without CaCl 2 brines and NaCl with CaCl 2 verify the mechanism.
brines are injected in to the core. The two pure NaCl Nasralla and Nasr-El-Din (2014) investigated
brines are designed with 2000 and 240,000 mg/L and the LSWF with contact angle measurement, zeta (z)
other brines have NaCl with 2000 mg/L and CaCl 2 potential measurement, and corefloodings of second-
with 10 or 100 mg/L. The injection of pure NaCl with ary and tertiary oil recoveries. Through the comprehen-
2000 mg/L produces higher oil production rate as well sive experiments, they tried to explain the reason of the
as the lower level of differential pressure compared improved oil recovery with EDL expansion. Various
with the injections of other brines. Based on these brines, which have TDS from 109 to 174,156 mg/L
observations of sandstone cores, this study concluded and pH from 4 to 7.6, are subject to the experiments.
that a major contribution on the increasing oil recovery The experiments measure the z-potentials of oil/brine
is the ionic concentration of brine, i.e., ionic strength, and Berea sandstone rock/brine interfaces by changing
rather than the Ca 2þ and Mg 2þ and proposed the brine type. The experimental results indicate that
electrical double layer (EDL) expansion theory as a z-potential of oil/brine is a function of salinity and
mechanism of LSWF. cation type. In addition, it is found that lower pH
Berg, Cense, Jansen, and Bakker (2010) carried out produces the less negative and closer to zero z-poten-
the experiments to find the direct evidence indicating tial. The contact angle is measured to confirm the
the exact mechanism of LSWF. They constructed exper- wettability alteration by changing brine pH and
imental system to visualize the microscopic detachment salinity. It is also tried to quantify the relation between
of crude oil from clay layer. The experiments monitor the wettability modification and z-potential change
the movement of oil droplets attached to montmoril- and develop the relation with the results of LSWF cor-
lonite clay layer as well as thickness of the layer, when eflooding. In the test of the tertiary recovery of LSWF,
salinity of injecting brine is changed from high salinity no additional oil recovery and increasing pressure
to low salinity. It is observed that approximately up to drop due to fine migration are observed (Fig. 1.9A).
80% of oil is released from the clay layer with the However, the secondary recovery of LSWF increases
minor swelling of the clay layer. It also reports no oil recovery up to 12% than high-salinity brine
deflocculation or release of clay particles. The study injection (Fig. 1.9B). The another coreflooding of
concluded that the LSWF increases oil recovery because LSWF investigates the effects of salinity, brine compo-
of wettability modification rather than fine migration sition, and pH on the secondary oil recovery. From the
and selective plugging via clay swelling. experiments, the study concluded that the expansion
Austad, Rezaeidoust, and Puntervold (2010) of EDL is controlled by salinity and pH and it increases
published the adsorption and coreflooding experiments the secondary oil recovery when injecting brine has
of LSWF to illustrate the effects of pH and salinity. The lower salinity and higher pH. The additional study of
adsorption measurement uses the kaolinite clay Shehata and Nasr-El-Din (2017) carried out various
powder, basic organic materials of quinoline, and acidic experiments including spontaneous imbibition, core-
organic material of 4-tert-butyl benzoic acid. The flood, computed tomography (CT) scan, X-ray diffrac-
adsorption of the organic materials on the clay power tion (XRD), X-ray fluorescence (XRF), scanning
is measured in the various ranges of salinity and pH electron microscope (SEM), nuclear magnetic reso-
conditions. In the low pH condition of 5, the increasing nance (NMR), and mercury injection capillary pressure
adsorption is observed as salinity decreases. In the high (MICP) tests. The extensive experiments intensively
pH condition of 8, the sensitivity of adsorption to the investigate the effect of connate water composition
salinity depends on the salinity and the degree of on the oil recovery of LSWF and observe that the diva-
adsorption is relatively low (Fig. 1.8). This observation lent cations in connate water significantly increase the
implies that an increase in pH has much higher impact oil recovery.