Page 101 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 4 Hybrid Chemical EOR Using Low-Salinity and Smart Waterflood 93

solution, but the change is not significant. Using the Johannessen and Spildo (2013) investigated the po-
fluids, the four sets of coreflooding are performed. tential of LSSF by comparing the optimum salinity sur-
Two coreflooding experiments are designed with sec- factant flood. The LSSF introduces the moderately low
ondary LSWF and tertiary LSSF. Additional oil recov- IFT, and the surfactant flood at optimum salinity brings
eries by about 32% and 30% are obtained by tertiary the ultralow IFT. Two North Sea crude oils and the
LSSF process, respectively. The increasing differential various versions of diluted seawater are prepared for
pressure and pH are observed during the tertiary LSSF. the experiments. The experiments include the phase
In the third coreflooding, the secondary injection of behavior test of microemulsion, IFT measurement, cor-
seawater is followed by the tertiary mode of LSSF. The eflooding, dispersion test, and dynamic retention mea-
tertiary LSSF enhances the oil recovery with the surement. The less water-wet Berea core by crude oils
increasing pH and differential pressure. These observa- aging is used for coreflooding. The low-salinity brine
tions are explained that the increasing pH is attributed is the diluted seawater by a factor of 0.07. The microe-
to the alkaline properties of the surfactant solution. mulsion system is composed of the water, surfactant,
The incremental oil recovery is higher in previous two cosurfactant, cosolvent, and crude oil. The solubiliza-
coreflooding experiments compared with the third cor- tion ratio and IFT by varying salinity and WOR are

eflooding experiment. The last coreflooding investigates experimentally measured at 50 C through phase
the performance of secondary LSWF and tertiary high- behavior test. The optimum salinity corresponding
pH LSWF. The slight increment of oil recovery by 7% one of the crude oils is determined as diluted seawater
is achieved for the tertiary process. The experimental by a factor of 0.43. The optimum salinity of surfactant
study drew a number of conclusions. The IFT reduction solution is relatively higher than the low salinity condi-
of surfactant is still effective in low salinity condition. tion, which is diluted seawater by a factor of 0.7. The
Stabilizing a low salinity environment can improve surfactant solution at optimal salinity condition is
the tertiary oil recovery of LSSF. The contribution of also observed to have ultralow IFT on the order of
pH increase by alkali addition is slightly effective for ter- 3 10 4 dyne/cm. The surfactant solution at low
tiary recovery of LSWF. salinity condition results in the moderately low IFT as
2
Alagic, Spildo, Arne, and Jonas (2011) further inves- 1.8 10 . Another crude oil is determined to have
tigated the performance of tertiary LSSF on the recovery the optimum salinity condition as diluted seawater by
of remaining oil after secondary LSWF and quantified a factor of 0.5. In a number of coreflooding tests, LSSF
the role of crude oil aging and initial wettability on and optimum salinity surfactant flood process are
the oil recovery of LSWF and LSSF. The same anionic compared (Fig. 4.23). The hybrid LSSF is designed to
surfactant and two different concentrations of surfac- follow the secondary or tertiary LSWF. The optimized
tant are prepared. The coreflooding experiments use surfactant flood also follows the secondary or tertiary
the aged cores, i.e., less water-wet, and unaged cores, optimum salinity waterflood. Significant increases in
i.e., water-wet. During the coreflooding of secondary oil recovery are observed when surfactant is injected
LSWF, the retardation of Mg 2þ is observed for the regardless of salinity condition. The additional oil re-
aged core. Because the mineral dissolution might coveries by LSSF range from 7% to 30%. The increments
compensate the retardation of Ca , the retardation of by 23.2%e37% are observed during optimum salinity
2þ
Ca 2þ is hardly measured for both aged and unaged surfactant flood. The relatively lower oil recovery in-
cores. The less water-wet core, aged core, shows the crease of LSSF than optimum surfactant flood is attrib-
less fine migration than the water-wet core, unaged uted to the higher performance of preflush LSWF
core. Less fine migration is consistent with extensive compared with that of preflush optimum salinity water-
studies of LSWF. The secondary LSWF also produces flood. The dispersion test is carried out to examine the
higher oil recovery in aged cores than unaged cores. heterogeneity of cores. The core cleaning process differ-
During the coreflooding of tertiary LSSF, the higher re- entiates the dispersion profiles from cores. It is
covery of remaining oil is obtained for high surfactant explained that residual oil is blocking the pore and
concentration and crude oileaged core system. During cleaning process eliminating the residual oil gives acces-
hybrid LSSF, the oil layer becomes destabilized at low sibility to the isolated and dead-end pore. Lastly, the
salinity condition and lower capillary pressure by sur- retention of surfactant is measured to validate the
factant injection mobilizes the trapped oil. The studies benefit of low salinity condition. The dynamic measure-
(Alagic et al., 2011; Alagic & Skauge, 2010) experimen- ment of retention monitors the produced surfactant
tally have demonstrated the potential of hybrid LSSF on concentrations of coreflooding experiments. The less
recovery from the less water-wet cores. retardation and higher total production of surfactant