Page 13 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 1 History of Low-Salinity and Smart Waterflood 5

100 100
(A) (B)
90 90

80 80
70 70
R wf (% OOIP) 50 R wf (% OOIP) 50 connate=invading S =20%
60
60
wi
S =23-27 %
wi
40
t =10 days
T a =55 °C connate=invading 40 CSRB T a =55°C
0.01CSRB
a
30 t a =7.0 days 0.1CSRB 30 0.1CSRB T d =55°C
=55 °C flood rate=6 ft/d
T d 0.01CSRB
CSRB
20 Flood rate=10 ft/d 20
10 10
0 0
0 5 10 15 0 2 4 6 8 10
Injected Water Volume (PV) Injected Brine Volume (PV)
FIG. 1.5 Effects of fine particles on the oil recovery of waterflood: (A) nonfired/acidized Berea sandstone, (B)
fired/acidized Berea sandstone. (Credit: From Tang, G.-Q., & Morrow, N. R. (1999). Influence of brine
composition and fines migration on crude oil/brine/rock interactions and oil recovery. Journal of Petroleum
Science and Engineering, 24(2), 99e111. https://doi.org/10.1016/S0920-4105(99)00034-0.)
increase, when the invading brine has low salinity. are measured and compared (Fig. 1.7). The concentra-
However, additional experiments using fired/acidized tions of the effluent brine drop lower than the concen-
sandstones or refine oils produce no change in oil trations in the injecting brine. The observations are
recovery. These results indicate that all factors of explained with adhering Ca 2þ and Mg 2þ onto rock ma-
connate and injection brines, crude oil, and the rock trix. Based on the observations of retardations of Ca 2þ
2þ
affect the sensitivity of oil recovery to brine composi- and Mg , a hypothetical mechanism of multicompo-
tion. Based on these observations, Tang and Morrow nent ionic exchange (MIE) is formulated for LSWF.
(1999) proposed the mechanism of fine migration Ligthelm et al. (2009) conducted the spontaneous
behind the LSWF. imbibition test and coreflooding using Berea and
Agbalaka, Dandekar, Patil, Khataniar, and Hemsath Middle Eastern sandstone cores. They tested various
(2008) conducted the coreflooding of LSWF as second- brines including pure NaCl brine, CaCl 2 brine, MgCl 2 ,
ary and tertiary recoveries. They monitored the change brine, and synthetic brine from Dagang to investigate
of residual oil saturation with variation in wettability, the role of divalent cations. In the spontaneous
salinity, and temperature. The brines to be tested have imbibition tests, it is found that both pure CaCl 2 and
salinities of 4%, 2%, and 1%. In the EOR potential MgCl 2 generally reduce residual oil saturation less
test, the experiments switch the injecting brine from than NaCl brine and the synthetic brine. These findings
high-saline brine to low-saline brine and elevate indicate that the multivalent cations of the brine make
temperature of injecting brine. They observe that the reservoir rock less water-wet. This interpretation is
residual oil saturation is reduced from 39% to 15% also inferred from the coreflooding. In the coreflooding
for decreasing salinity and increasing temperature experiment, the Berea sandstone core to be tested is
(Fig. 1.6). Another study by Lager, Webb, Black, saturated with 2400 mg/L NaCl brine and Brent Bravo
Singleton, and Sorbie (2008) also evaluated the crude oil. This core is flooded by 2400 mg/L NaCl brine
potential of LSWF as secondary and tertiary recoveries. following 24,000 mg/L CaCl 2 brine. Although there is
The study recorded pH of effluent fluid as well as oil negligible possibility of formation damage, increasing
recovery. In addition, it carried out the ion analyses to differential pressure is observed during CaCl 2 brine
explain the LSWF in terms of geochemistry. In the ion injection. In addition, when the brine injection is
analyses, the concentrations of divalent cations changed from CaCl 2 brine to NaCl brine, the oil pro-
(Ca 2þ and Mg ) between injecting and effluent brines duction is resumed despite the differential pressure
2þ