Page 106 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

98 Hybrid Enhanced Oil Recovery using Smart Waterflooding

with the LSSF (Fig. 4.28). The LSSF with only Mg 2þ the smallest range of pore size. In line with the results
addition produces slightly less oil production of in situ contact angle measurement, the LSSF recovers
compared with the LSSF. This experimental study oil from the smallest range of pore size section. As a
demonstrated that optimizing the brine composition result, the LSSF shows the higher EOR production
can enhance the oil production of cationic surfactant than LSWF and high-salinity surfactant flood, which is
flood in carbonates. closer to the optimum salinity surfactant. In addition,
Mirchi (2018) published the pore-scale investigation the oil production can be enhanced when secondary
to quantify pore-scale fluid configurations through sys- LSWF process is applied ahead of tertiary LSSF. This
tematic coreflooding. The systematic coreflooding is study visually demonstrated the higher performance
developed to be integrated with the micro-CT scanner. of hybrid LSSF displacement by configuring the micro-
The systematic apparatus measures the in situ contact scopic fluid distribution and in situ contact angle distri-
angle and visualizes the pore space and fluid occupancy bution in oil-wet system. A couple of conclusions are
during the carbonate coreflooding. The experiments use drawn from the study. The LSSF significantly modifies
two different brines of high salinity and low salinity. the wettability of oil-wet carbonates and is effective to
The cationic surfactant of 0.2 wt% is added to the recover the trapped oil in the corners or crevices and
brines, and conventional surfactant solution and low- small size of pores. The performance of LSSF can be
salinity surfactant solutions are prepared. The IFTs improved with preflush LSWF.
between brines/surfactant solution and crude oil are Teklu et al. (2018) extended the application of LSWF

determined at 500 psi and 80 C. The low-salinity brine and LSSF to the recovery from liquid-rich Bakken shale
shows the lower IFT than the high-salinity brine. When reservoir. The spontaneous imbibition test evaluates the
the cationic surfactant is present, the high-salinity brine shale oil recoveries by LSWF and LSSF processes. The
results in lower IFT than the low-salinity brine. These three Bakken shale cores have permeability in the range
observations indicate the high salinity condition is close of 0.001e2.74 md and porosity in the range of 5.29%
to the optimum salinity of microemulsion system. e7.71%. The Bakken shale crude oil has TAN of
The systematic apparatus measures the in situ con- 0.09 mg KOH/g and TBN of 1.16 mg KOH/g. The
tact angle during coreflooding and constructs the distri- high-salinity water of 240,000 ppm KCl and low-
bution of in situ contact angle (Fig. 4.29). The salinity water of 20,000 ppm KCl are synthetically pre-
distribution indicates the pore-scaled wettability. The pared. The anionic surfactant of 1000 ppm is added to
distribution of in situ contact angle shows that initial the brines. The LSWF shows higher oil recovery by
core is estimated to have average in situ contact angle about 14% compared with the high-salinity waterflood.
with 140 degrees and wettability is determined to be Although the oil recovery during surfactant process is
oil-wet. The injections of high-salinity water and low- not quantitatively measured, the oil recoveries of the
salinity water reduce the average in situ contact angle. spontaneous imbibition tests are visually investigated.
The LSWF decreases the contact angle more compared When the low-salinity water is switched to the low-
with the conventional waterflood injecting high- salinity surfactant solution, some oil droplets are
salinity water. When the surfactant is added in the expelled from the cores. However, the high-salinity sur-
low-salinity brine, the average in situ contact angle is factant solution does not show further extrusion of oil

highly reduced below 100 C. The remaining oil in oil- droplets from core after high-salinity water. The oil pro-
wet system after waterflood is easily trapped in the cor- duction of LSSF from the spontaneous imbibition test is
ners and crevices. The distributions of the remaining oil briefly explained with driving mechanisms including
are observed before coreflooding and after LSWF or osmosis, capillary pressure, wettability modification,
LSSF (Fig. 4.30). The distribution of remaining oil indi- and IFT decrease.
cates that the LSSF is effective to reduce the trapped oil
compared with the LSWF. In addition, the performance Numerical simulations
of the injection is analyzed according to the pore size. Tavassoli, Korrani, Pope, and Sepehrnoori (2016)
The pore size is categorized with four sections. For the developed the numerical simulation of LSSF imple-
smallest pore size ranging the order of 100e200 mm, menting the mechanisms of surfactant flood and
the LSSF is still effective to decrease in situ contact angle LSWF and comprehensive geochemical reactions. The
(Fig. 4.31). The oil extraction from each pore size range study applied the in-house simulator of UTCHEM-
is estimated. Major oil production is attributed to the IPhreeqc to simulate the LSWF and LSSF based on the
mobilization of oil in largest pore size range. The addi- sandstone experimental results of Alagic and Skauge
tion of surfactant enables extraction of more oil from (2010). Because the geochemical reactions are of