Page 19 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 1 History of Low-Salinity and Smart Waterflood 11

experimentally reported the sensitivity of potential- Ca 2þ has 3.4 times higher affinity toward chalk surface
2 2þ 2þ
determining ions, the ratio of SO 4 to Ca , and tem- over Mg in the low temperature. In high temperature

perature to the oil recovery of spontaneous imbibition with 130 C, the production of Mg 2þ is seemed to be
test (Fig. 1.12). They verified the previous observations more retarded than that of Ca 2þ (Fig. 1.13). In addition,
of Strand et al. (2006) to modify wettability of chalk the effluent concentration of Ca 2þ is higher than the
because of the injection of SO 4 2 and high initial concentration of Ca . After two pore volume
2þ
temperature. (PV) injection, the effluent concentration of Ca 2þ
Zhang, Tweheyo, and Austad (2007) reported the decreases to the initial concentration of Ca . These
2þ
potential of Mg 2þ as the potential-determining ion observations explained a substitution reaction between
as well as Ca 2þ and SO 4 2 . The study evaluated the Mg 2þ and Ca 2þ on the chalk surface. The brine to
impacts of Mg 2þ present in seawater on spontaneous be used in chromatographic test has the equivalent
imbibition, z-potential, chromatographic test, and concentrations of Ca 2þ and Mg 2jþ . Because the seawater
coreflooding. They tested the different brines adjusting has about four times higher concentration of Mg 2þ than
2þ 2þ 2 2þ
concentration of Ca ,Mg , and SO 4 . The the concentration of Ca , the seawater injection intro-
z-potential measurements use milled outcrop chalk duces a pronouncing substitution reaction between
2þ
form Steven Klint near Copenhagen, Denmark. In Mg 2þ and Ca . The another series of spontaneous
the tests, the increasing z-potential is observed with imbibition tests are designed to configure the interac-
2þ
an increase in the concentration of Mg . This observa- tion between different potential-determining ions of
2þ
tion implies the potential of Mg 2þ to adjust the charge Ca ,Mg 2jþ , and SO 4 2 . The spontaneous imbibition
density on chalk surface. The coreflooding tests at low tests vary temperature from 70 to 130 C and concentra-

and high temperature conditions are carried out tions of Ca ,Mg , and SO 4 2 (Fig. 1.14). In the tests
2þ
2þ
to confirm the potential of Mg 2þ according to tempera- at 70 C, brines have the zero concentrations of Ca 2þ

2
2þ
2þ
ture. In the test, brine containing Ca ,Mg , and and Mg , but the concentration of SO 4 from zero to
2þ
SCN 1 is flooded into chalk core. The chromatographic four times of seawater. In all brine cases, the only
2þ
2þ
test analyzes the effluent concentrations of Ca ,Mg , 10% of oil recovery is observed. In the tests at 100 C,

and SCN 1 obtained from the coreflooding. In the low no additional oil is observed until the either of Ca 2þ
temperature with 23 C, the productions of both Ca 2þ or Mg 2þ is added into the brines. These results indicate

and Mg 2þ are delayed compared with the production that SO 4 2 without Ca 2þ or Mg 2þ has no potential to
of SCN and, especially, there is more delay in the modify wettability increasing imbibition. When the
production of Ca 2þ compared with the production of Ca 2þ or Mg 2þ is added in the brines, all cases
2þ
Mg . The result approximately estimates that the show the increasing oil recoveries from 20% to 42%.
70
60
Recovery (OOIP%) 40 130°C (Oil A, AN=2.07)
50
30
20
100°C (Oil A, AN=2.07)
10 70°C (Oil B, AN=0.55)

0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0
2+
[SO 4 2- /Ca ]
2 2þ
FIG. 1.12 Correlation between oil recovery, ratio of SO 4 to Ca in imbibing fluids, and temperature
effects. (Credit: From Zhang, P., & Austad, T. (2006). Wettability and oil recovery from carbonates: Effects of
temperature and potential determining ions. Colloids and Surfaces A: Physicochemical and Engineering
Aspects, 279(1), 179e187. https://doi.org/10.1016/j.colsurfa.2006.01.009.)