Page 181 - Characterization and Properties of Petroleum Fractions - M.R. Riazi

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TABLE 4.4—Calculation of pseudoproperties of the natural gas system of Example 4.1.
P ci ,bar
T ci , C
Component
No. QC: —/— T1: IML 4. CHARACTERIZATION OF RESERVOIR FLUIDS AND CRUDE OILS 161
◦
M i
x i
x i × M i
ω i
x i × P ci
x i × ω i
x i × T ci
1 H 2 S 0.012 34.1 100.38 89.63 0.0942 0.41 1.20 1.08 0.0011
2 N 2 0.002 28.0 −146.95 34.00 0.0377 0.06 −0.29 0.07 0.0001
3 CO 2 0.01 44.0 31.06 73.83 0.2236 0.44 0.31 0.74 0.0022
4 C 1 0.90 16.0 −82.59 45.99 0.0115 14.40 −74.33 41.39 0.0104
5 C 2 0.048 30.1 32.17 48.72 0.0995 1.44 1.54 2.34 0.0048
6 C 3 0.017 44.1 96.68 42.48 0.1523 0.75 1.64 0.72 0.0026
7 iC 4 0.004 58.1 134.99 36.48 0.1808 0.23 0.54 0.15 0.0007
8 nC 4 0.005 58.1 151.97 37.96 0.2002 0.29 0.76 0.19 0.0010
9 iC 5 0.001 72.2 187.28 33.81 0.2275 0.07 0.19 0.03 0.0002
10 nC 5 0.001 72.2 196.55 33.70 0.2515 0.07 0.20 0.03 0.0003
Sum Mixture 1.00 18.17 −68.24 46.74 0.0234
b. The system is a natural gas so Eqs. (4.1) and (4.2) are used ω for SCN groups from C 6 to C 45 . Whitson used Riazi–Daubert
to estimate pseudocritical properties using SG g as the only correlations (Eqs. (2.38), (2.50), (2.63), and (2.64)) to generate
available input data. critical properties and molecular weight from T b and SG. He
also used Edmister method (Eq. (2.108)) to generate values of
T pc = 93.3 + 180.6 × 0.6274 − 6.9 × 0.6274 2
acentric factor. As discussed in Chapter 2 (see Section 2.10),
= 203.9K =−69.26 C these are not the best methods for calculation of properties of
◦
2
P pc = 46.66 + 1.03 × 0.6274 − 2.58 × 0.6274 = 46.46 bar. hydrocarbons heavier than C 22 (M > 300). However, physical
properties reported by Katz and Firoozabadi have been used
c. To calculate the effects of nonhydrocarbons present in in reservoir engineering calculations and based on their tab-
the system Eqs. (4.5) and (4.6) are used to calculate ad- ulated data, analytical correlations for calculation of M, T c ,
justed pseudocritical properties. These equations require P c , V c , T b , and SG of SCN groups from C 6 to C 45 in terms of
mole fractions of H 2 S, CO 2 , and N 2 , which are given in N C have been developed [10].
= 0.002. Un-
Table 4.4 as: y H 2 S = 0.012, y CO 2 = 0.01, and y N 2 Riazi and Alsahhaf [16] reported a new set of data on prop-
adjusted T pc and P pc are given in Part c as T pc =−69.26 C erties of SCN from C 6 to C 50 . They used boiling point and
◦
and P pc =−46.46 bar.
specific gravity data for SCN groups proposed by Katz and
Firoozabadi from C 6 to C 22 to estimate PNA composition of
T c =−69.26 − 44.44 × 0.01 + 72.22 × 0.012
pc each group using the methods discussed in Section 3.5.1.2.
◦
−138.89 × 0.002 =−69.12 C. Then Eq. (2.42) was used to generate physical properties of
P c = 46.46 + 30.3369 × 0.01 + 41.368 × 0.012 paraffinic, naphthenic, and aromatic groups. Properties of
pc SCN from C 6 to C 22 have been calculated through Eq. (3.39)
− 11.721 × 0.002 = 47.24 bar.
using the pseudocomponent approach. These data have been
Although use of Eqs. (4.1) and (4.2) together with Eqs. (4.5) used to obtain coefficients of Eq. (2.42) for properties of
and (4.6) gives reliable results for natural gas systems, use SCN groups. The pseudocomponent method produced boil-
of Eqs. (4.3) and (4.4) for gas condensate systems or gases ing points for SCN groups from C 6 to C 22 nearly identical to
that contain C 7+ fractions is not reliable. For such systems those reported by Katz and Firoozabadi [14]. Development of
properties of C 7+ fractions should be estimated according to Eq. (2.42) was discussed in Chapter 2 and it is given as
the methods discussed later in this chapter. c
(4.7) θ = θ ∞ − exp(a − bM )
where θ is value of a physical property and θ ∞ is value of θ
4.3 CHARACTERIZATION AND PROPERTIES as M →∞. Coefficients θ ∞ , a, b, and c are specific for each
OF SINGLE CARBON NUMBER GROUPS property. Equation (4.7) can also be expressed in terms of
carbon number, N C . Values of T b and SG from C 6 to C 22 have
As shown in Tables 4.1 and 4.2, compositional data on reser- been correlated in terms of N C as
voir fluids and crude oils are generally expressed in terms of 2/3
mol (or wt) percent of pure components (up to C 5 ) and SCN (4.8) T b = 1090 − exp 6.9955 − 0.11193N C
groups for hexanes and heavier compounds (C 6 ,C 7 ,C 8 ,..., (4.9) SG = 1.07 − exp 3.65097 − 3.8864N 0.1

C N+ ), where N is the carbon number of plus fraction. In C
Table 4.1, N is 10 and for the crude oil of Table 4.2, N is where T b is in kelvin. Equation (4.8) reproduces Katz–
40. Properties of a crude oil or a reservoir fluid can be ac- Firoozabadi data from C 6 to C 22 with an AAD of 0.2% (∼1K)
curately estimated through knowledge of accurate properties and Eq. (4.9) reproduces the original data with AAD of
of individual components in the mixture. Properties of pure 0.1%. These equations were used to generate T b and SG for
components up to C 5 can be taken from Tables 2.1 and 2.2. By SCN groups heavier than C 22 . Physical properties from C 6
analyzing the physical properties of some 26 condensates and to C 22 were used to obtain the coefficients of Eq. (4.7) for
crude oils, Katz and Firoozabadi [14] have reported boiling SCN groups. In doing so the internal consistency between
point, specific gravity, and molecular weight of SCN groups T c and P c were observed so that as T b = T c , P c becomes
from C 6 up to C 45 . Later Whitson [15] indicated that there is 1 atm (1.013 bar). This occurs for the SCN group of C 99
inconsistency for the properties of SCN groups reported by (∼M = 1382). Coefficients of Eq. (4.7) for N C ≥ C 10 are given
Katz and Firoozabadi for N C > 22. Whitson modified proper- in Table 4.5, which may be used well beyond C 50 . Data on
ties of SCN groups and reported values of T b , SG, M, T c , P c , and solubility parameter of SCN groups reported by Won were

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