Page 121 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

CHAPTER 5 Hybrid CO 2 EOR Using Low-Salinity and Smart Waterflood 113

EFFECT OF SALINITY ON THE SOLUBILITY Caudle and Dyes (1958), uses the water to support
IN WATER the CO 2 EOR process. The first interesting scheme of
The presence of salt or electrolyte in an aqueous solution miscible gas-water injection is the simultaneous water
modifies the solubility of organic components in water. and CO 2 injection (Caudle & Dyes, 1958). Then, the
The phenomena of salting-out effect have been termed CO 2 water-alternating gas (CO 2 WAG) process is
less soluble organic components in aqueous salt solu- proposed and extensively investigated (Christensen,
tions than in pure water. The empirical Setschenow equa- Stenby, & Skauge, 2001; Rogers & Grigg, 2001). The
tion (Setschenow, 1889) has been developed to describe water injection of the CO 2 WAG process offers an
this effect. Until the work of Harvey and Prausnitz improvement in an inherent unfavorable mobility ratio
(1989), the investigation of EOS model considering between the solvent and oil to secure the recovery
the salinity-dependent solubility is limited. Most of the mechanism of CO 2 EOR process. Some studies of
studies considering the effect are applicable to only CO 2 WAG have explored the effects of CO 2 solubility
low pressure and low temperature conditions. In addi- into water and brine salinity on the performance of
tion, they used the methods that are not appropriate to CO 2 WAG process. When the injected CO 2 contacts
the system containing supercritical gases. Harvey and water during CO 2 WAG process, some of CO 2 dissolves
Prausnitz (1989) developed the EOS model to be appli- in water. The CO 2 dissolution in water might prevent
cable to the high pressure condition. The developed EOS some of CO 2 from contacting oil, contribute to lower
model accounts for the intermolecular effects by the oil recovery efficiency, and change the formation
ionic effects and conventional intermolecular forces for volume and viscosity of water. The CO 2 solubility in
nonelectrolytes. The model also uses the Setschenow brine is sensitive to pressure, temperature, and salinity
constant. Although the model accurately predicts the of the water. The CO 2 solubility in brine increases
salting-out effects under the low salt condition less with the increasing pressure and decreasing salinity. In
than 1 molal concentration, it underpredicts the addition, the recent studies of CO 2 WAG process have
salting-out effect in moderate to high salt conditions. been interested in the usage of low-salinity water or
Søreide and Whitson (1992) provided the novel smart water, rather than conventional high-salinity
approach to predict the mutual solubilities of brine/ water, during the water injection period. The studies
hydrocarbon mixtures with an EOS at high pressure have investigated whether the low salinityeaugmented
and high temperature conditions in addition to CO 2 WAG (LS-CO 2 WAG) process introduces both
describing the effect of salinity in aqueous phase. mechanisms of CO 2 injection and LSWF.
The model accurately predicts the experimental results
of hydrocarbons, CO 2 ,N 2 ,and H 2 S in pure water and EXPERIMENTS
NaCl brine.
Kulkarni and Rao (2005) investigated the performances
of miscible and immiscible CO 2 WAG processes
CO 2 WATER-ALTERNATING GAS INJECTION comparing with CGI and suggested the optimum design
The injection of solvents has been of interest to the of CO 2 WAG process to maximize economics. In the
additional oil extraction from porous media. The analysis of CO 2 WAG, the effect of brine salinity
solvent injection recovers the oil by incorporating the is investigated by using both 5% NaCl brine and multi-
extraction, dissolution, vaporization, solubilization, component reservoir brine from the Yates Field in West
condensation, or other phase behavior changes with Texas. The n-decane and Berea sandstone core are
crude oil, which contribute the oil recovery mechanisms subjected to the experiments. Before the coreflooding
including the oil viscosity reduction, oil swelling, experiments, a couple of approaches determine the
solution gas drive, and oil extraction. In the early MMP of decane to define the displacement experiments
1960s, the small injection of liquefied petroleum gas to be either miscible or immiscible condition. Based on
(LPG) has been investigated for the solvent process. the data from literature studies, empirical equation,
The high cost of the LPG is a barrier for the practical and numerical simulation, the MMP of the decane is
implementation. In the late 1970s, the CO 2 has become estimated as 1880 psi. Immiscible and miscible floods
the widely used solvent. Orr and Taber (1984) are performed at 500 and 2500 psi, respectively. In
both conditions, the secondary recovery is performed
proposed the usage of CO 2 for EOR process. The CO 2
injection has a number of injection process designs, with waterflood. The tertiary CGI and CO 2 WAG follow,
which include the combination of continuous, respectively. During the water injection, the two brines
alternating, and chase fluid injection schemes. The of 5% NaCl and Yates Field brine of 9200 mg/L TDS
miscible gas-water injection, originally proposed by are used. During the secondary waterflood using both