Influence of the Crude Oil Characterization on Mmp Calculation
C A L C U L AT I O N
J.-N. JAUBERT 0
L. ARRAS 0
E. NEAU 0
0 (3) Rsidence Michelet-Delattre , 5, boulevard du Gnral-Koenig, 13009 Marseille - France
Institut national polytechnique de Lorraine1 Faculté des sciences de Luminy2
(1) Laboratoire de thermodynamique des sparations,
cole nationale suprieure des industries chimiques,
1, rue Grandville,
54001 Nancy Cedex - France
(2) Laboratoire de chimie physique,
163, avenue de Luminy,
13288 Marseille Cedex 9 - France
INFLUENCE DE LA CARACTRISATION D'UN PTROLE
BRUT SUR LE CALCUL DE LA PRESSION MINIMALE DE
Dans cet article, nous tudions lÕinfluence de la modlisation des
coupes dÕun ptrole brut sur la valeur calcule de la pression
minimale de miscibilit (MMP). En particulier, il est expliqu quels
types de constituants peuvent tre regroups sous forme d'un
peusdo-constituant sans pour autant dgrader la valeur de la
MMP. La procdure suivie dans cet article est simple : partir dÕun
ptrole brut donn, nous utilisons dans un premier temps une
reprsentation par 37 composants, exploitant lÕinformation
analytique standard disponible sur ce fluide. La modlisation des
fractions lourdes utilise est celle dveloppe par Avaulle et al.
(1997a), dans laquelle nous avons ajust deux paramtres du
rsidu de distillation C20+ sur les pressions de saturation
exprimentales. Sur le fluide tudi, nous mettons en vidence le
bon niveau de restitution des grandeurs volumtriques, des
donnes exprimentales de gonflement ainsi que de la MMP
mesure lors d'une exprience de dplacement en tube mince.
Dans un deuxime temps, les composs intermdiaires lourds, les
intermdiaires moyens et les composants lgers font
successivement lÕobjet de regroupement en pseudo-constituant. L'influence
de tels regroupements sur la valeur calcule de la MMP est alors
INFLUENCE OF THE CRUDE OIL CHARACTERIZATION
ON MMP CALCULATION
This paper focuses on the influence of the crude oil
characterization on minimum miscibility pressure (MMP)
calculation. It is shown what kind of compounds may be lumped
together in order to calculate the MMP with a good accuracy. In a
first step, a selected crude oil is modeled with 37 pure compounds
using the characterization procedure developed by Avaulle et al.
(1997a) in which two parameters of the distillation residue are fitted
on the experimental bubble points. In this context, all the
experimental data (PVT, swelling test, slim tube test) are
calculated with a very good accuracy. In a second step, the heavy
intermediate, the middle intermediate and the light compounds are
successively lumped. The influence of such lumping procedure on
the calculated MMP is discussed.
INFLUENCIA DE LA CARACTERIZACIîN
DE UN PETRîLEO CRUDO RESPECTO AL CçLCULO
DE LA PRESIîN MêNIMA DE MISCIBILIDAD
En este artculo se estudia la influencia de la modelizacin de las
fracciones de un petrleo crudo con respecto al valor calculado de
la presin mnima de miscibilidad calculada (MMP). Bsicamente,
REVUE DE L’INSTITUT FRANÇAIS DU PÉTROLE
VOL. 53, N° 1, JANVIER-FÉVRIER 1998
se indica qu tipos de componentes se pueden reunir en forma de
un seudocomponente sin por ello degradar el valor de la MMP. El
procedimiento seguido para este artculo es sencillo : tomando
como punto de partida un petrleo crudo determinado, utilizamos
en una primera etapa una representacin por medio de
37 componentes, en cuyo caso se utiliza la informacin analtica
estndar disponible en este fluido. La modelizacin de las
fracciones pesadas utilizada es aquella desarrollada por Avaulle
y sus colaboradores (1997a), en la cual hemos ajustado dos
parmetros del residuo de destilacin C20+ en las presiones de
saturacin experimentales. Se hace resaltar, para el fluido
estudiado, el correcto nivel de restitucin de las magnitudes
volumtricas, de datos experimentales de aumento de volumen,
as como de la MMP medida con motivo de una experiencia de
desplazamiento en tubo delgado. En una segunda etapa, los
compuestos intermedios pesados, los intermedios medianos y los
componentes livianos, son sucesivamente objeto de reagrupacin
en seudocomponente. Se analiza entonces la influencia de
semejantes reagrupaciones sobre el valor calculado de la MMP.
It is well known from the literature
the miscibility process, when a gas is injected into a
crude oil, is controlled by a sequence of nc-1 key tie
lines if nc is the number of components present. There
is the initial tie line (the tie line that extends through the
original oil composition), the gas tie line (the tie line
that extends through the injected gas composition) as
well as nc-3 intermediate tie lines called crossover tie
lines as initially defined by
Monroe et al. (1990)
. In this
context, the minimum miscibility pressure (MMP)
which is a key parameter in a gas injection project
design must be defined as the lowest pressure at which
any one of these nc-1 tie lines becomes a critical
tie-line. However, in softwares currently available in
petroleum companies, a crude oil is usually described
by a maximum of 10 components or
pseudocomponents meaning that some hydrocarbons are
lumped together in order to reduce computing times. It
is obvious that such a lumping procedure makes
disappear many key tie lines and may lead to very
different values of the MMP. The goal of this study is to
test the influence of such lumping procedures on the
calculated MMP value.
1 EXPERIMENTAL DATA
A crude oil for which many PVT experiments were
performed by the French Petroleum Company
TOTAL SA was selected. The composition of the
reservoir fluid and the results of the True Boiling Point
(TBP) distillation are shown in Table 1.
The following experimental data are available:
– Bubble points, total densities and relative volumes
measured during constant mass expansions
performed at three different temperatures
(t1 = 87.8°C, t2 = 103.3°C and t3 = 121.1°C). The
reservoir temperature is t2. In such experiments,
the relative volume (Vtot Vsat ) is defined as the total
cell volume divided by the liquid volume at
– Liquid densities, compressibility factors of liberated
gas and Bo measured during a differential
vaporization at the reservoir temperature.
It is recalled that Bo = (Vliq Vref ) is defined as the
liquid volume divided by a reference volume
(liquid volume at the final pressure measured under
atmospheric conditions: 15°C, 1 atm). It is thus
possible to calculate the relative volume
( Bo Bosat ) defined as (Vliq Vsat ) where Bosat is the
Bo value at the bubble point.
– Bubble points and densities of the reservoir oil
swollen with a lean gas at the reservoir temperature
– The minimum miscibility pressure MMP (slim tube
test) when the lean gas used during the swelling test
is injected into the reservoir crude oil.
The composition of the injection gas is shown in
Table 2. All the experimental data are summarized in
Tables 3 to 6.
RP2Tcc2 exp êëêém × èçae1 - èae TTcøö 0.5 ø÷ö úûúù
In order to calculate correct densities, the molar
volume v, solution of the EoS must be reduced using a
volume translation c as proposed by
Péneloux et al.
v correct = veos - c
with c = RTc [0.1153758 - 0.440642ZRA ]
In the previous equation, ZRA is the Rackett
compressibility factor appearing in
modification of the Rackett Equation.
For a mixture containing p compounds of mole
fraction xi, classical mixing rules were used:
bm = å xibi cm = å xici
am ( T ) = å å [ ai(T ) × a j(T ) xi × x j(1 - kij(T ))]
with kij(T ) =
d i =
ai( T )
Eij(T ) - (d i - d j )
2d i d j
The binary interaction energies Eij were estimated
using the group contribution method developed by
Abdoul et al. (1992)
3 CRUDE OIL MODELING
According to the EoS described in the previous
section, each component of a petroleum fluid is
characterized by the following parameters:
critical temperature Tc
critical pressure Pc
acentric factor w
Rackett compressibility factor ZRA
atomic group fractions allowing the calculation of the
binary interaction parameters (bips).
3.2 The intermediate compounds
In this study, each cut from C11 to C19 was modeled
according to the method recently developed by
Avaullée et al. (1997a). In this approach, each cut is
in a first step modeled as a mixture of three pure
compounds (one paraffin, one naphtene and one
aromatic). The relative amount of these three molecules
is determined in order to reproduce the experimental
molar weight and density of the cut. The critical
properties and the acentric factor of these three pure
compounds are estimated using the group contribution
method developed by Avaullée et al. (1997b). In
a second step, these three compounds are lumped
together in order to model a given cut by one
pseudocomponent only. The critical temperature, critical
pressure and acentric factor of this pseudo-component
are solution of a non-linear three equation system
(Avaullée et al., 1997a)
. The Rackett compressibility
factor and the group fraction allowing to estimate the
bips are calculated by additivity balanced by the
corresponding relative amounts.
3.3 The C20+ residue
Once more, the method developed by Avaullée et al.
(1997a) was used in order to model the C20+ residue
by a single compound. In order to use the PR EoS, the
critical temperature, critical pressure and the shape
parameter m must be estimated. Avaullée et al. (1997a)
developed a specific correlation allowing the
calculation of the critical pressure knowing the critical
temperature and suggest to tune the critical temperature
and the m parameter on the experimental bubble points
of the crude oil. Since in this study, three saturation
pressures were experimentally determined, this method
can be used. The Rackett compressibility factor of the
residue is determined so that the density calculated
using the cubic EoS matches the experimental one.
Moreover, the knowledge of the experimental molar
weight and density of the C20+ compound allows
to determine the group fractions necessary to estimate
4 CALCULATION OF THE PVT
3.1 The light compounds
For light compounds (until C10), all these parameters
are known in the literature.
Before performing MMP calculations, the crude oil
modeling previously described was used in order to
check whether it was accurate to reproduce with a good
accuracy the experimental data. The evolution of
the relative volume versus pressure for the four
depletions, the PT phase envelop and the P-X diagram
corresponding to the swelling test are shown on
Figures 1 to 6. Moreover, during the swelling test
simulation, the densities of the saturated mixtures of
reservoir oil and injected gas were calculated with
a 0.8% deviation. The average overall deviation
between calculated and experimental total densities
obtained during constant mass expansions was 1.6%.
During the differential vaporization simulation, the
liquid phase densities and the liberated gas
compressibility factors deviated respectively of 1.5%
and 0.7% from experimental data. In conclusion, the
characterization procedure used allows a very
satisfactory estimation of the various PVT data.
5 MMP CALCULATIONS
5.1 Results using the complete crude oil compositional model
In a first step, the previous crude oil modeling was
used to calculate the MMP when the gas, the
composition of which is given in Table 2, was injected
in the reservoir crude oil. Before performing such a
calculation, it is necessary to determine the process
mechanism: pure vaporizing (VGDM), pure condensing
(CGDM) or mixed condensing/vaporizing (C/VM).
For the fluids investigated in this study, the
mechanism was found to be a mixed C/V mechanism
as discovered by
. In this case, the MMP
may be determined using either a multicell approach
developed by Zick but never published, or a classical
commercial 1D simulator. The first solution was chosen
in this study. The results of the calculations are shown
in Table 7 and evidence a very good agreement
between experimental and calculated MMP. Indeed,
the deviation observed is less than 3% which is the
experimental uncertainty in the determination of the
MMP using a slim tube.
Comparison between calculated and experimental MMP using a
37 component characterization for the crude oil
200 300 400
Relative volume Vtot/Vsat versus pressure during a constant mass
expansion performed on the selected crude oil at t3 = 121.1°C.
Relative volume Vliq/Vsat versus pressure during a differential
vaporization performed on the selected crude oil at t2 = 103.3°C.
experimental saturation pressures
calculated phase envelop
P-T phase envelop of the selected reservoir crude oil.
experimental bubble pressures
calculated phase envelop
5.2 Results using different compositional models
In this section it was decided to lump together
successively the middle intermediate components
(from C11 to C19), the light intermediate components
(from C5 to C10), the light hydrocarbons (from C1 to C4)
and to compute the MMP. A similar lumping procedure
was applied to the injected gas composition.
The pseudoization (lumping procedure) used in this
paper was the very simple API method. In order to
lump together n compounds of internal mole fractions
xi in a pseudo-component k, the following formulae
Vck = å xiVci with Vci =
(in this study Zci was merged with ZRAi )
å xiVc i Tc i
w k = å xiw i
ZRAk = å xiZRAi
n ê ç
Pc k = åi=1 xi Pc i êê1 - b × çç1
n Tc k ÷÷ úúú
å xiTc i ÷ø ú
b = 5.808 + 4.93w k
On the other hand, atomic groups of
pseudocomponent k were calculated knowing those of
compounds i and the internal mole fractions xi.
The complete results are shown in Table 8.
Table 8 clearly evidences that it is not conceivable
to lump together the light components to calculate
Indeed, the calculated value is very far from the one
obtained using the complete modeling of the crude oil
and the process mechanism is not the same.
Effect of various clustering configurations on the calculated MMP
Using 37 components a crossover tie line controls
the miscibility process whereas the initial oil tie line
does control the miscibility when light compounds are
On the other hand, lumping together either the
compounds from C5 to C10 or from C11 to C19 gives a
calculated MMP close to the one obtained with the
complete compositional model. It is interesting to
notice that lumping together the middle intermediate
compounds makes decrease the MMP whereas lumping
together the light intermediate components makes
increase the MMP. In a last step, it was decided to
model the crude oil with only 12 components
introducing simultaneously both pseudo-components
"C5-C10" and "C11-C19". The calculated MMP was thus
MMP = 325 bars, what is very close (1.9% deviation)
to the reference value. In this later case, the number of
components has been reduced by a factor three and
computing times by a factor 10.
This paper showed that:
– the characterization procedure developed by
Avaullée et al. is suitable for MMP calculation;
– The MMP may be calculated with the same
accuracy, modeling the crude oil with 37 or
12 compounds. To do so, the light intermediate
compounds and the heavy intermediate compounds
have to be lumped into two pseudo-components;
– Lumping together the light compounds is not
Abdoul W. , Rauzy E. and Péneloux A. ( 1992 ) A group contribution equation of state for correlating and predicting thermodynamic properties of weakly polar and non-associating mixtures. I. Binary and multicomponent systems . Fluid Phase Equilib., 68 , 47 - 102 .
Avaullée L. , Neau E. and Jaubert J.N. (1997a) Thermodynamic modeling for petroleum fluid . II. Prediction of PVT properties of oils and gases by fitting one or two parameters to the saturation pressures of reservoir fluids. Fluid Phase Equilib ., 139 , 171 - 203 .
Avaullée L. , Neau E. , Trassy L. and Jaubert J.N. (1997b) Thermodynamic modeling for petroleum fluid. I. Equation of state and group contribution for the estimation of thermodynamic parameters of heavy hydrocarbons. Fluid Phase Equilib ., 139 , 155 - 170 .
Johns R.T. ( 1992 ) Analytical theory of multicomponent gas drives with two-phase mass transfer . PhD Stanford University, Stanford, CA.
Monroe N.N. , Silva M.K. , Larsen L.L. and Orr F.M. ( 1990 ) Composition paths in four component systems: effect of dissolved methane on 1D CO2 flood performance . SPERE , 423 - 432 .
Péneloux A. , Rauzy E. and Frèze R. ( 1982 ) A consistent correction for Redlich-Kwong-Soave volumes . Fluid Phase Equilib., 8 , 7 - 23 .
Peng D.Y . and Robinson D.B. ( 1976 ) A new two-constant equation of state . Ind. Eng. Chem . Fund., 15 , 59 - 64 .
Rauzy E. ( 1982 ) Les méthodes simples de calcul des équilibres liquide-vapeur sous pression . PhD University of AixMarseille III.
Spencer C.F. and Danner R.P. ( 1973 ) Prediction of bubble point density of mixture . J. Chem. Eng. Data. , 18 , 230 - 234 .
Trebble M.A. and Bishnoï P.R. ( 1987 ) Development of a new four-parameter cubic equation of state. Fluid Phase Equilib ., 35 , 1 - 15 .
Zick A.A. ( 1986 ) A combined condensing/vaporizing mechanism in the displacement of oil by enriched gases . SPE 15493 , 1 - 11 .
Final manuscript received in December 1997