Page 82 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

74 Hybrid Enhanced Oil Recovery using Smart Waterflooding

to the maximum adsorption capacity, the buffer zone of CaCO 3 ). The injecting brine has the salinity of about
low-salinity water forms behind the connate water and 69,000 mg/L and the hardness of 9000 mg/L. The smart
the head of polymer front in porous media. Although water or low-salinity water is prepared by the dilution
the buffer zone can protect the rheology of low- of the injecting brine by a factor of 10. The core and
salinity polymeric solution from the interference by dead crude oil for the experiments are obtained from
high-salinity connate water, it delays the oil recovery. the target reservoir. The dead crude oil has viscosity of
Although the study addressed the promising benefits about 4.39 cp at the reservoir condition. Because the
of LSPF, it also cautioned a couple of potential risks to crude oil has gas-oil ratio less than 100 scf/bbl, the vis-
be involved in LSPF. The usage of low-salinity water cosity of crude oil is close to that of dead oil. Conse-
during LSPF disturbs the original equilibrium state in quently, the experiments using the dead oil accurately
the reservoir and causes the reequilibrium. During represent that using live oil.
the reequilibrium by low-salinity water intrusion, the In the study, the first experiment measures the
cation exchange of the clay and low salinity in the rheology of sulfonated polyacrylamide polymer at three

bulk solution might destabilize the clay and lead to temperatures of 25, 40, and 60 C. The viscosity of poly-
more clay swelling by a double layer expansion. In addi- meric solution is measured as polymer concentration
tion, the reequilibrium might involve the mineral disso- and brine type of makeup brine change. Because the
lution, which increases the multivalent cations in the reservoir temperature is higher than the experimental
solution causing chemical degradation of polymer. temperatures, the viscosity model of power law is con-
The electrostatic interaction between the polyelectrolyte structed using the experimental rheology measurements
polymer and the clay surface also can be affected by the and the viscosity of polymeric solution at the reservoir
reequilibrium process. It is concluded that the evalua- temperature is estimated. For a target viscosity of
tions of the positive benefits and negative risks are 11 cp, it is determined that 30% of polymer concentra-
required to do a full economics evaluation of LSPF tion can be reduced when the brine type is switched
and optimization to improve the economic viability from the injecting water to low-salinity water. The injec-
of the hybrid process. tion scheme of coreflooding is designed considering the
Previous studies have observed the increasing oil result of rheology experiments. The second experiment
production by the synergy of LSPF and measured the using PALS technique measures an electrophoretic
improving polymer rheology and stability by using mobility and estimates a surface electrokinetics poten-
the low-salinity water as makeup brine. However, they tial, i.e., z-potential, in the various binary systems of a
have not demonstrated whether the LSPF still secures crushed reservoir rock sample and a variety of poly-
the mechanism of LSWF or not. They only explained meric solutions. The polymeric solutions are prepared
that the higher recovery of LSPF than polymer flood at different concentrations of polymer and different
or LSWF is the evidence of securing the mechanism of brine types. It is, conventionally, known that successful
LSWF with the assistances from the improving rheology LSWF decreases the potential toward negative of
and stability of polymer. z-potential. Firstly, the experiments measure the electro-
A couple of studies (AlSofi et al., 2016, AlSofi, Wang, phoretic mobility and calculate the z-potentials of the
& AlBoqmi, 2018) have evaluated the synergy between high-salinity injecting brine and low-salinity water
chemical EOR and smart waterflood and evaluated the without polymer (Fig. 4.7). Both the mobility and po-
possibility of the hybrid EOR on the oil recovery in- tential show positive values for injecting brine and
crease in a more realistic framework. The studies have negative values for low-salinity water. It is clearly
investigated both the polymer flood and surfactant demonstrated that the LSWF possibly introduces the
flood as chemical EOR candidates. Experiments with wettability modification compared with the conven-
polymer flood are only illustrated herein and those tional waterflood. The various polymeric solutions, us-
with surfactant flood will be discussed later. The studies ing the injecting brine or low-salinity water as makeup
tried to clarify the possible synergy by performing a brine, are investigated (Fig. 4.8). It is observed that the
suite of experiments including electrokinetics potential, presence of polymer shifts the electrophoretic mobility
contact angle, rheological, coreflood, and NMR tests. from positive to negative values for the high-salinity
The target reservoir is the slightly viscous Arabian heavy injecting brine. Because the polymer has the anionic
carbonate reservoir and has the high temperature and charges on the backbone and a group of counterions
high salinity conditions. The temperature is about in the bulk solution can form an electrical double layer
99 C, and connate water has the salinity of about around the charged component in polymer, the effects

244,000 mg/L and hardness of 58,000 mg/L (as of the potential-determining ions might be shielded