Page 54 - Hybrid Enhanced Oil Recovery Using Smart Waterflooding

46 Hybrid Enhanced Oil Recovery using Smart Waterflooding

observed when injecting fluidisswitchedfrom dissolution in the aqueous phase is required. Although
seawater to low-salinity water. The numerical simula- the numerical study of Omekeh et al. (2012) considered
tion indicates that the ion exchange causes the high the effect of solubilized CO 2 in aqueous phase on the
retention of Ca 2þ , but carbonate mineral dissolution geochemistry, it assumed the aqueous solubility
generating Ca 2þ in water slightly reduces the degree without thermodynamics calculations. However,
of retention. The combined geochemical reactions Nghiem et al. (2004) calculated the aqueous solubility
contribute to the retention of effluent history of of CO 2 incorporating the equilibrium relationship be-
Ca 2þ . In the experiment, a slight reduction in the tween aqueous and gases phases. The equilibrium rela-
effluent concentration of Mg 2þ is also observed when tion of CO 2 between aqueous and gaseous phases is
the injecting fluid is switched from formation water described in Eq. (3.48). A phase equilibrium process de-
to seawater. The numerical simulation explains termines the solubility of CO 2 in aqueous phase and is
that ion-exchange reaction reduces the effluent modeled by the equality of fugacities between aqueous
concentration of Mg 2þ . Because the seawater has and gaseous phases as shown in Eq. (3.49). The EOS
higher concentration of Mg 2þ over formation water, model (Peng & Robinson, 1976) calculates the fugacity
the ion-exchange reaction replaces the adhered ions in gaseous phase, and either Henry’s law (Li & Nghiem,
with Mg 2þ on the negative sites of the clay surface. 1986) or Søreide-Whitson-Peng-Robinson (Søreide &
The study also examined the effluent pH as the result Whitson, 1992) calculates the fugacity in aqueous
of geochemical reactions. In the results of pH, the phase. Eq. (3.50) indicates the Henry’s law, and the
numerical simulation illustrates that the dissolution Henry’s constant in the law is a function of temperature
of calcite is sensitive to the pH of brine. The and pressure following Eq. (3.51).
low-salinity water has relatively high pH, and the injec-
CO 2 ðaqÞ4CO 2 ðgÞ (3.48)
tion of low-salinity water contributes to less mineral
dissolution compared with the injections of formation f i;g ¼ f i;aq (3.49)
water and seawater. This numerical simulation study (3.50)
f i;aq ¼ H i x i
successfully developed the LSWF process coupled Z
with geochemistry and explained the experimental s 1 p
ln H i ¼ ln H þ v i dp (3.51)
i
results from a geochemical point of view. However, RT p H 2 O
s
the numerical model employs the limited number of where f i,j indicates the fugacity of species i, i.e., CO 2 ,
geochemical reactions. in the phase j, H i is the Henry’s constant of species i,
Nghiem, Sammon, Grabenstetter, and Ohkuma x i is the mole fraction of species i in aqueous phase,
(2004) advanced the GEM software, developed by H is the Henry’s constant at the saturation pressure of
s
CMG (Computer Modelling Group, Ltd.), coupled i s
H 2 O, temperature, and zero salinity, p is the satura-
with the comprehensive geochemical reactions. The H 2 O
tion pressure of H 2 O, and v i is the partial molar volume
GEM software is the multiphase, multicomponent,
of species i.
and equation of state (EOS) simulator and also has a
The Henry’s constant at the H 2 O saturation pressure
capability to model the geochemical reactions. Later,
and temperature also depends on the pressure and tem-
Dang, Nghiem, Chen and Nguyen (2013) advanced
perature, and it is determined with the following Har-
the GEM simulator to model the LSWF considering
vey’s relation (Harvey, 1996). Harvey (1996)
comprehensive geochemical reactions. Before the
published the correlations of Henry’s constant at the
description of work of Dang et al. (2013), the important
H 2 O saturation pressure and temperature to handle
features of Nghiem et al. (2004) are discussed.
the effects of pressure and temperature for a few gaseous
The purpose of the Nghiem et al. (2004) is to model
components (CO 2 ,N 2 ,H 2 S, and CH 4 ). For CO 2 , the
the CO 2 storage process in saline aquifers. The
following correlation of Eq. (3.52) estimates pressure
geochemical reactions include the aqueous reaction, and temperature dependent of the Henry’s constant
mineral dissolution and precipitation, and ion on the basis of saturation pressure of H 2 O and reduced
exchange. The gaseous CO 2 has the solubility in the temperature. Saul and Wagner (1987) provided the
aqueous phase, and the aqueous solubility of CO 2 is saturation pressure of H 2 O at the temperature. The
of importance in the mechanisms of CO 2 storage. partial molar volume of CO 2 is also defined to calculate
Because the dissolved CO 2 in brine influences the pH the Henry’s constant. Garcia (2001) presented the
of brine and mineral reactions are highly affected
correlation of partial molar volume of CO 2 as a
by the pH of brine, the accurate modeling of CO 2
function of temperature as shown in Eq. (3.53).