A multicomponent oil-cracking kinetics model for modeling preservation and composition of reservoired oils

Pergamon

0146-6380(93)E0012-B

Org. Geochem. Vol.21, No. 8-9,pp. 911-925, 1994 Copyright ((S)1994ElsevierScienceLtd Printed in Great Britain.All rights reserved 0146-6380/94$7.00+ 0.00

A multicomponent oil-cracking kinetics model for modeling preservation and composition of reservoired oils LUNG-CHUANKuo and G. ERIC MICHAEL Conoco Inc., I000 South Pine, Ponca City, OK 74602-1267, U.S.A. (Received 1 September 1993; returned for revision 21 October 1993; accepted 20 November 1993)

Abstract--Accurate assessment of the preservation of crude oils is essential for evaluating the economics of deep petroleum accumulations. This paper describes a multicomponent kinetics model which calculates the extent of cracking, API gravity, GOR, and composition of reservoired oils as a function of the initial oil composition, residence time, and thermal/burial history of the reservoir. This model uses the program PMOD developed by Lawrence Livermore National Laboratory (LLNL) as the software platform. It contains ten petroleum components; the density and composition of each component was determined based on literature data. Its reaction network contains seven cracking reactions with activation energies (E) that range from 37.1 to 80.0 kcal/mol and Arrhenius factors (A) from 3.838E21 to 2.844E34my-~. A reaction network was created for a waxy oil and one for a nonwaxy oil by using the published IFP experimental data as calibration. A method was developed to derive the input oil composition by combining data from reservoir fluid analysis, liquid chromatography, and whole-oil gas chromatography. Several output examples are presented. In addition, field data from the Jurassic Smackover Trend in northern Gulf of Mexico are used to test and demonstrate the application of the model. The present model may be used not only to model oil cracking but to identify secondary alteration (such as biodegradation and fractionation) in reservoired oils. Future research is needed to test the sensitivity of the parameters, to create reaction networks for other types of oils, and to incorporate the pressure effect into the model. Key words---oil preservation, oil cracking, computer model, kinetic modeling, reservoir geochemistry, petroleum alteration

INTRODUCTION Modeling hydrocarbon generation, migration, accumulation, and preservation is essential for determining the quantity, composition, and distribution of petroleum reserves in a given basin. Petroleum hydrocarbons are in thermodynamic disequilibrium under geologic conditions and constantly evolve towards more stable forms which include simple gases (such as methane and carbon dioxide), aromatic compounds (such as benzene, toluene, xylenes), and coke. As a result, black oils which survive in shallower reservoirs may turn into lighter oils, condensates, or gases in progressively deeper reservoirs. Accurate assessment of the oil preservation limit is, therefore, essential for evaluating the economics of deep petroleum accumulations. This paper presents a multicomponent kinetics model for modeling cracking of reservoired oils. This model is different from the existing oil cracking models in two aspects. First, this model uses multiple E - A sets to model oil cracking, whereas existing models use either a single E - A set (e.g. Tissot et al., 1987; Welte et aL, 1988) or multiple E with a single A (e.g. Mackenzie and Quigley, 1988, Behar et aL, 1991) to model oil cracking. Single E - A models frequently underestimate the preservation limit of crude oils because they do not

take into account complex reactions involved in oil cracking. Multiple E-single A models ignore the covariation between E and A (referred to as compensation effect) in many reactions including hydrocarbon cracking (Boudart, 1968; Sekhar and Ternan, 1979). Second, the present model focuses on the cracking of reservoired oils, thus mass balance is maintained only among the initial oil and its cracking products. Most existing models (e.g. Braun and Burnham, 1992; Behar et al., 1992) handle oil generation (primary cracking) and oil cracking (secondary cracking) as a closed system, thus mass balance is maintained between kerogen, oils, and oil-cracking products. However, oils generated from source rocks, as assessed by the analysis of shale extracts and/or pyrolysis experiments, often do not represent oils accumulated in reservoirs. Oils remaining in source rocks are continually altered by thermal maturation, and differences between reservoired oils and those remaining in source rocks arise from primary migration (Leythaeuser et al., 1988; Wilhelms et al., 1990), secondary migration (England et al., 1991), mixing of oils from different sources (Hiilebrand and Leythaeuser, 1992), and secondary alteration processes such as phase separation (Thompson, 1987; Larter and Mills, 1991). The present model uses the composition of reservoired oils as initial input regardless of their origin. The secondary

911

t~12

LUNG-CHUANKUO and G. Eglc MICHAEL

cracking mechanisms in the Braun and Burnham (1992) model can also be used in a similar manner. THE MULTICOMPONENTOIL CRACKINGKINETICS MODEL

Software platform The present model was developed by using the program PMOD created by Lawrence Livermore National Laboratory (Burnham and Braun, 1990; Braun and Burnham, 1990, 1992) because it can handle complex chemical reactions with a combination of parallel, serial, competing, and reverse mechanisms. Such unparalleled capability makes it possible to design complex reaction networks to more accurately predict the composition, API gravity, and GOR of reservoired oils as a function of initial oil composition and the extent of oil cracking. Selection o f components Oil cracking is modeled by specifying cracking reactions of several organic compound groups (components). These components were selected based on the following considerations: first, density and organic geochemical data must be available for the selected components so that the oil cracking model developed can be calibrated with accuracy. Second, the components selected must cover the entire spectrum of crude oil composition and their proportions can be determined readily and accurately. The ten components selected for the present model include methane (CI), ethane (C2), wet gases (C3-5), gasoline-range hydrocarbons (C6-14), stable aromatic compounds (BTXN, C~5+ saturate (SAT), Cjs+ aromatic (AROM), resin (NSO), asphaltene (ASPH) compounds, and coke (COKE) (Table 1). Coke, stable aromatic carbon compounds, and methane appear only as the cracking products, whereas the other seven components are reactants and products in the reaction network. Elemental composition o f the components Only hydrogen and carbon are considered in the models developed in this study (Table 1). An average

H/C ratio of 1.25 for the ASPH fraction and 1.36 for the NSO fraction was estimated from data on similar material (Koots and Speight, 1975; Clementz, 1976; Czarnecka and Gillott, 1980; Waxman et al.; Orr, 1986; Ungerer et al., 1981; Hirschberg, 1984; Tissot and Weite, 1984; Cornelius, 1984; Meyerhoff and Meyer, 1984; Curiale, 1986). The elemental composition of hydrocarbon components in oils was estimated from Tissot and Welte (1984), Behar et al. (1991), and Ungerer et al. (1988). The waxy oil has slightly lower H/C ratio in the SAT fraction and slightly higher H/C ratio in the C3-5 component than the nonwaxy oil which reflects, on average, the longer carbon-carbon chain length of the Cls+ compounds and shorter carbon-carbon chain length (i.e. more gassy) of the wet gas compounds in waxy oils. The H/C ratio of coke is close to 0.5 (Ungerer et al., 1981). This ratio decreases slightly with increasing thermal maturity, as is indicated by the experimental data of Ungerer et al. (1988). Specific gravity o f the components Heavy oils are composed primarily of resins (NSO) and asphaltenes (ASPH) with corresponding specific gravities in the range of 0.9-1.2 g/era 3 (Curiale, 1984; Sweeney, 1990; Meyerhoff and Meyer, 1984; Ungerer et al., 1981; Hirschberg, 1984). The specific gravities of other components were determined from the data of representative compounds in each class (Weast, 1985; Sweeney, 1990). The BTXN fraction represents benzene, toluene, xylene, and naphthalene which have specific gravities from 0.8611 to 0.9625 g/cm 3 (Weast, 1985). The AROM fraction includes compounds such as phenanthrene and methylphenanthrenes, which have specific gravities of 0.96741.060g/cm 3. The SAT fraction contains paraffins, branched alkanes, and cyclic saturated compounds. The specific gravity of paraffins and cyclic saturated compounds can range from approximately 0.7886 g/cm 3 (eicosane, C20) to 0.8584g/cm 3 (squalene, C30). The C~5 fractions are approximated by C3-5 and C6-14 components with specific gravities of 0.64 and 0.78 g/era 3, respectively (Sweeney, 1990).

Table I. Physical and chemicalproperties of petroleum components used in the present multicomponentoil crackingkineticsmodel Formula Specific API gravity* gravity Waxy Nonwaxy (g/era3) (degrees) Fraction Symbol Asphaltenes ASPH CHI2s CHI25 1.060 2.0 Resins NSO CH136 CHI.36 0.995 10.7 C~5+ aromatics AROM CH~.4o CH~.4o 0.930 20.7 C~5+ saturates SAT CH2.os CH2.~o 0.875 30.2 Stable aromatics't BTXN C H ~ o CHHo 0.875 30.2 C6-.~4 C6-14 CHI.6O CHi.6o 0.780 49.9 C3 5 C3-5 CH2.4~ CHz.~ 0.640 89.6 C2 C2 CH2.so CHzso --C~ CI CH4oo CH4.oo ..... Coke COKE C C . . . . Coke COKE H H --*Density of liquids under standard temperature-pressure(STP) conditions. tlncludes benzene, toluene,xylenes,and naphthalenes.

Modeling preservation and composition of reservoired oils 70

[ •

Sulfur Content < 1.0 wt~. [

=/

60

o~

50

•

o../.

o h'- ,*0 "0

~

30

0 :3 0

o

/

20 10 0

0

I 10

I

I

f

I

I

20 30 40 50 60 Measured API Grovlfy

70

Fig. I. A correlation between the modeled and measured API gravity of 34 crude oils.

API gravity of the components P M O D calculates API gravity from the specific gravity that is derived as the mass-weighted harmonic mean of the specific gravities of the individual oil fractions at standard temperature and pressure conditions (Braun and Burnham, 1990). The API gravity of crude oils is, therefore, calculated based on the assigned specific gravity of the individual components at STP conditions. Because the components representing large molecule groups (such as ASPH and NSO) have wide range of specific gravity and the effect of molecular interaction of functionalized groups of resin and asphaltene compounds on specific gravity is not taken into account in the calculation, it is necessary to calibrate the API gravity built in the model by data from crude oils. In the present model, the API gravity of 34 crude oils of various compositions was calculated from their composition (in wt%) with the built-in specific

913

gravity and compared to the measured API gravity. The result (Fig. I) shows that the specific gravity model in Table I provides a reasonably accurate estimation of the API gravity of these crude oils ( < 1 0 % error in most cases) between 20 and 60 degrees API. On the other hand, the present model overestimates the API gravity by more than 10% of those low-API gravity oils which contain more than 1.0% sulfur. This is probably due to the fact that sulfur is not taken into consideration in the present model, and incorporation of sulfur to form sulfursulfur and sulfur-carbon bonds generates more dense structures (with higher specific gravities) than similar structures with only carbon and hydrogen (e.g. 1,3dithiolane with a specific gravity of 1.259 g/cm 3 vs pentane with a specific gravity of 0.6262 g/cm3). Sulfur is present to a greater extent in asphaltenes and resins, and the specific gravity of these compounds increases with increasing sulfur content. This can be estimated by Specific Gravity = 0.023 S + 0.886 (for resins) Specific Gravity = 0.019 S + 0.952 (for asphaltenes) (where S is sulfur content in wt % which can be obtained from elemental analysis) which are derived based on the data of Tippee (1990). However, based on our data from Orr (1986), correction of the specific gravity of resins and asphaitenes alone is not sufficient to properly model API gravity of high-sulfur crude oils, which implies that a significant a m o u n t of sulfur is also present in hydrocarbon fractions. The effect of sulfur in crude oil cracking and API gravity prediction needs to be studied in the future.

Reaction network The reaction network in the present model is composed of seven reactions with ASPH, NSO, A R O M , SAT, C6-14, C3-5, and C2 as the reactant for each reaction. A reaction network has been established for a Boscan oil (a nonwaxy, marinesourced oil from Venezuela) and one for a Pematang oil (a waxy, terrestrial-sourced oil from Indonesia) (Table 2). These two oils were chosen because highquality, detailed oil cracking experimental data are

Table 2. Chemicalreaction network for two crude oils in the present multicomponentoil cracking kinetics model Best'an oil (aoawaxy) ASPH-*0.0703 NSO + 0,1401 AROM + 0.0060 SAT + 0.4768 C6-14 + 0.3068 COKE NSO--,0.0917 AROM + 0.5059 C6--14+ 0.1313 BTXN+ 0.1855 ASPH + 0.0856 COKE AROM--,0.7543 C6-14 + 0.0860 ASPH+ 0.1597 COKE SAT--*0.0411C3-5 + 0.4399 C6-14 + 0.5190 C2 C6-14--*0.2097C3-5 + 0.1736 C2 + 0.1885 NSO + 0.0256 BTXN+ 0.1879 AROM + 0.2147 COKE C3--5-*0.8889C2 + 0.l 111 C6--14 C2--~.0660 CI + 0.9271 C3--5+ 0.0069 C6-14 Pmstm~ oH(waxy) ASPH--*0.0579NSO + 0.1155 AROM + 0.0049 SAT + 0.3818 C6-14 + 0.4399 COKE NSO-*0.0765 AROM + 0.4101 C6-14 + 0.1096 BTXN+ 0.1548 ASPH + 0.2490 COKE AROM--*0.4928C6-14 + 0.2232 ASPH + 0.2840 COKE SAT-*0.9000 C6-14 + 0.1000 C2 C6-14--,0.5678 C3-5 + 0.0292 C2 + 0.3558 NSO + 0.0472 BTXN C3-5---~0.9000C2 + 0.1000 C6-14 C2--~.0343 CI + 0.9587 C3-5 + 0.0070 C6-14

914

LUNG-CHUAN Kuo and G. ERICMICHAEL 0.

3~.

l

F

:

0.3~ 1

i

o.7_"

cAROM ~,~T

o O.ZE ,o

0 ' 0 . 1 ~-

O. IE

a,

0.0 =_ i

0 0

2

4

6

i

i

1

I.~

0,~ ~

0

.

6

2

8

0 . 3 ~ - - -

•

• NSO + /~:q'l + AROM + SAT

NrXN + C6-14

0.2~

0,7 o

o.ed

0.6

o

"20.5 g

0.4

0,?

•

0.2

0.0~

I

0. 2

4

• 0 L

6

0

-

2

4

E

~ - -

f

• C1 • COKE

0.5

0.3E~

o0"25

t

e

~

:: o.eo #

0.1

0.0! 0t 0

0.3

I

I

I

2

4

6

Time,

8

hr

0

2

4 Time,

6 hr

Fig. 2. Calibration of the present multicomponent oil cracking kinetics model based on the IFP experimental data on a Boscan oil.

available (Ungerer et al., 1988; Behar et al., 1991) for calibration. The entire reaction network is calibrated by extensive iteration until the calculated compositional variations of the component agree reasonably well with those observed in laboratory experiments. Figures 2 and 3 compare the present muiticomponent oil cracking model (shown in solid curves) with the IFP experimental data (shown in symbols). The match is very good considering the difference between IFP and Conoco in component composition definition and analytical procedure as well as experimental error. The cracking of resin and asphaltene compounds to generate saturated and aromatic hydrocarbons is a forward reaction (Tissot and Welte, 1984; Bjoroy et al., 1988; Behar et al., 1991). Experimental data also indicate that resins and hydrocarbon compounds polymerize to form asphaltenes and coke in a reverse reaction (Philips et al., 1985; Bjoy et al., 1988). This

is taken into account by the reaction in which NSO is the reactant. The products of reactions in which AROM, SAT, C6--14, C3-5, and C2 are reactants have been identified mainly by Ungerer et al. (1988) and Behar et al. (1991). The use of toluene/benzene/ xylene and naphthalene compounds as a stable carbon fraction is supported by experimental (Erdman and Dickie, 1964; Nowak and Gunschel, 1983; Bjorodoy et al., 1988) and field (Manowitz et al., 1990) data, which indicates that the amount of toluene and benzene increases with temperature and the extent of thermal cracking. Activation energy and Arrhenius

factor

Table 3 lists the activation energy and Arrhenius factor for each cracking reaction in the present multicomponent kinetics model. The activation energy for the cracking of resins is derived from the experimental data by Magaril (1973). The activation

Modeling preservation and composition of reservoired oils 6, ~.,

!

m~ a A.~q

915

i

i

$SAT

6.!

8.2~ 6 . ~.

o

6.~ 6.6. ~

6.1 $

|

•

6 0

2

4

i

i

Z O. 4~

i

e NSO.l-lk~

8.S

6

6

+ h~OM + SAT

6 . 3 =.

i

4

6

)

l

•

•

BT'XN

+

C6-14

6.3~ 6,

.o

6.2~

O. o

6.

6.15

O. 6.1~

6,, O. ~15

6.1

e

@ 6

6.E

2 i

i 4 l

•

i 6

6

I Z

, I 4

I 6

!

6.45

,

i

i

C2

+

C3-5

¢ ci " COKE

6.49a. 3~-

8.'I

8.3~-

0 ~6.

e.ea-

IX

O. I~F.

0.8 l Z

I

I

4

6

6

Time s hr

8

2

4

6

Time s h r

Fig. 3. Calibration of the present multicomponent oil cracking kinetics model based on the IFP experimental data on a Pematang oil.

energy for the cracking of asphaltenes are determined based on experimental data on asphaltic oils (Shu and Venkatesan, 1984). Data from whole-oil hydrous Table 3. The activation energy and Arrhenius factor for the present multicomponeot oil cracking kinetics model Reactant ASPH NSO AROM SAT C6-14 C3-5 C2

E (kcal/mol)

A (I/s)

37.1 40.7 54.9 55.7 58.6 (65.0) 62.5 (75.0) 65.9 (80.0)

] .247E08 1.462E09 2.707EI3 4.630E 13 3.425E 14 (2.850EI6) 5.058EI 5 (2.851 El9) 5.327EI6 (9.014E20)

Note: the values in parentheses are recommended by the authors due to theoretical considerations and calibration using other crude oil data.

pyrolysis (Bjoroy et al., 1988) support lower activation energies for resin and asphaltene cracking (24.5-31.0 kcal/moi), but the effect of water on cracking kinetics has not been assessed (Price, 1993; Monin and Audibert, 1988). A low activation energy for asphaltene cracking is also supported by a recent study by Bianco et al. (1993) which shows that even under mild heating conditions, asphaltene dealkylation and alkyl chain length reduction occur rapidly. Asphaltenes can still occur in small concentrations in light oils, but they are likely to be intermediate in H/C ratio between original asphaltene and highly aromatic coke. A more accurate model for asphaitene cracking probably should take into account both dehydrogenation, which occurs at low activation energies and results in large decrease in H/C ratio (e.g. 1.16-0.81), and condensation of the more aromatic residual asphaltenes (H/C = 0.81), which occurs at a higher activation energy (14kcal/mo]

916

LUNG-CHuAN K u o a n d G . ERIC MZCHAEL Table 4. An example of determining the input composition for the present multieomponent oil cracking kinetics model

20] 0 ~d.(ll~) 18

•, <

~

•

~

Step l (tin) ,t d. 0oTe)

a= ~

/

./

• Shue~0H4)

16 "

•

+ Fa~l~ ~ at (t~NS) • K~ et 8. 0 m )

I

/'~

14

/

10

8

Slog

6

A = 0.3 E -

4

3.045

Component*

Mol %

Molecular weight (g/tool)

Methane Ethane Propane I-butane N-butane I-pentane N-pentane Hexanes Heptanes Octanes Nonanes Decanes Undecanes Dodecanes plus

40.59 12.83 7.24 1.40 3,65 1.27 1.72 2.64 3.36 3.56 2.99 2.09 1.60 15.06

16 30 44 58 58 72 72 86 100 114 128 142 156 247*

wt % 8.68 5.15 4.26 1.08 2.83 1.22 1.66 3.03 4.49 5.43 5.12 3.97 3.34 49.74

Step 2 wt %

20

1o

3o

40

5o

6o

70

E (kcal/mole)

Component

Fig. 4. A correlation between activation energy and Arrhenius factor for cracking of crude oils with different composition. The straight line represents the statistical fit of the data (R 2 = 0.964).

higher) than the dealkylation reactions as suggested by Bianco et al. (1993). The activation energy values for the cracking of Cls+ AROM, Cls+ SAT, C6-14, C3-5, and C2 components were derived from Behar et al. (1991); their data suggest that the activation

80

70

q)

60 O{O 1:3Y

F ~'

@

50,

1

U

O0 a

v ~J

4O

30

~l

[] Experimentaldoto .11 The present model

20 0 10

20

30 40 50 60

70 80

@0 100

°API Gravity Fig. 5. A relationship between API gravity and activation energy for oil cracking used in the present model (with a statistical fit) and determin#d by laboratory experiment (Keith et al., 1993; McNab et al., 1952; Henderson and Weber, 1965; Shu and Venkatesan, 1984; Krishna et al., 1988; Horsfieid et al., 1992).

CI C2 C3-5 C6-14 SAT AROM NSO ASPH

From step I

Methane removed

8.68 5.15 11.05

. . 5.64 12.10

75.12

82.26

With liquid chromatography data .

. 5.64 12.10 36.45 45.81

5.64 12.10 36.45 16.09 14.65 8.29 6.78

*From reservoir fluid analyses.

energy for cracking of these components is insensitive to oil type. The Arrhenius factors for cracking reactions are determined based on a correlation between E and ,4 for cracking of crude oils with wide composition range (Fig. 4). The covariation between E and A (the compensation effect) is expected because theories of molecular reaction dynamics (e.g. Benson, 1976: Atkins, 1978) state that the collision frequency of molecules must be higher in order for a reaction which requires higher acivation energy to occur. In other words, a reaction with greater energy barrier to overcome is partially compensated through more vigorous collision of molecules involved in that reaction. It is important to note that the covariation between E and A shown in Fig. 4 is not the same as that observed in kinetic analysis of kerogen pyrolysis (Ungerer, 1990; Nielsen and Dahl, 1991; Barth and Nielsen, 1993) because the latter is a result of solving the kinetic equation for non-isothermal case (e.g. Mianowski and Radko, 1992). In Fig. 4, each E - A pair is a unique solution of the Arrhenius equation based on time-dependent experiment at a number of different temperatures over a wide temperature range. Thus, linear regression of these data represents a true compensation effect (Boudart, 1968) which reflects the different nature of chemical bonding in crude oils with different composition. The laboratory kinetic parameters can be applied to geological reactions, but the mechanisms or ratc

Modeling preservation and composition of reservoired oils

c~.~-

Fig. 6. A 3-D plot illustrating the increase in API gravity with reservoir temperature and residence time for an initial 30 degree API oil. limiting steps of these reactions may be different between laboratory and geologic conditions. Recent studies (e.g. Domin6, 1989, 1991) suggested that the activation energy for cracking of low molecular weight hydrocarbons may be considerably higher in nature than that observed in the laboratory under high temperature and low pressure. The cracking mechanism is postulated to change at lower temperatures (<200°C) and higher pressures as common in sedimentary basins (Hesp and Rigby, 1973; Mallinson et al., 1992; Von Kopsch, 1992). In ad-

90

Residence Time = 50 my

INPUT OF THE M U L T I C O M P O N E N T KINETICS M O D E L

70 6O 50

O-

0~ 40 30

Y

20 10

I

,

I

,

I

J

I

,

I

,

I

,

I

,

I

i

I

I

i

20 40 60 80 100120140 160180200 Reservoir

Ternperafure

(°C)

Fig. 7. An example showing the variation in the API gravity of cracked oils as a function of reservoir temperature and initial API gravity for a residence time of 50 my. Four initial API gravity values were modeled. 0(3 21 ,'8-9~G

dition, field and laboratory data (Mango, 1990, 1991, 1992; Hayes, 1991; Price, 1993) suggest that some hydrocarbon components are thermally very stable below 150°C for millions or billions of years. For these reasons, the authors recommend that the E values be increased for the reactions in which C6-14, C3-5, and C2 are the reactants (Table 3) when this model is applied to basin modeling. Iteration using PMOD shows that increasing the activation energies of the cracking reactions for C6-14, C3-5, and C2 components to the 65-80 kcal/mol range does not affect the fit between the modeled and experimental data; the model is more sensitive to the H/C ratio of the components than to the activation energy at advanced degree of oil cracking. An exception to the recommendation of the higher activation energies is when modeling high sulfur crude oils. Modeling of a high sulfur crude (7.2 wt %) (data from Orr, 1986) indicated that lower activation energies give modeled results most similar to measured laboratory data. Relatively few low temperature oil cracking experiments have been performed (Bjoroy et al., 1988; Domin6, 1991; Mango, 1991; Domin6 and Enguehard, 1992) due to the very slow reaction rate. However, this is certainly an important area for future research. The API gravity and activation energy for cracking of the petroleum components in the present model has a correlation which is also shown by the experimental data on the cracking of natural crude oils (Fig. 5). The large range of activation energy for a given API gravity of natural crude oils very likely reflects the compositional diversity of these oils. This further suggests the inadequacy of single E - A models and the need for multicomponent kinetics model for modeling oil cracking.

~l~

80

c.~

917

The present multicomponent kinetics model predicts the cracking of oil based on its initial composition in the reservoir, and the oil composition used is dependent on the objective of the modeling. In many cases, it is reasonable to use a low-maturity, nonbiodegraded, present-day oil composition to represent the composition of the oil at the time of emplacement because this composition may remain unchanged in low-temperature reservoirs for tens of millions of years (see next section). In such cases, the modeled results provide reliable estimation on the minimum API gravity of an oil to be expected at a given drilling depth in an area. Oil composition input data are essential for accurately predicting the GOR, API gravity, and composition of oils with increasing extent of cracking. A method combining the data from reservoir fluid analysis, liquid chromatography, and whole-oil gas chromatography was developed for this purpose. Table 4 provides an example. Reservoir fluid analysis is converted into wt% by using appropriate molect,-

LUNG-CHUAN K U O a n d G . ERIC MICHAEL

918

Table 5. Examples of compositional variation o f a crude oil during cracking under different modeling conditions. The initial temperature is 100"C for all cases Composition (wl %)

Residence time (my) ........................................................ 0 10 20 40 60 70 80 90

100

110

120

130

140

Waxy oil reaction network, I°C/my heating rate ASPH NSO AROM SAT C6- 14 C3~ 5 C2 BTXN COKE CI

7. I 17.0 23.2 36.7 15.9 0.1 0 0 0 0

0.2 4.2 24,8 36.7 25.4 0.1 0.1 1.5 7.0 0

0 0.1 25.2 36.7 27.7 0.1 0.1 1.9 8.2 0

0 0 23.9 36.6 29.2 0.1 0.1 1.9 8.2 0

0 0 9.2 19.1 54,0 0.1 1.8 2.0 13.8 0

0 0 0,4 1.4 73.0 1,8 3.8 2.1 17.5 0

0 0 0 0 63.2 10.2 4.6 3.2 18.8 0

0 0 0 0 26.9 35.6 6.2 6.9 24.4 0

0 0 0 0 0.9 50.1 I1.1 9.7 28.2 0

0 0 0 0 0 34.4 27.3 9.8 28.5 0

0 0 0 0 0 10.5 49.0 10.5 29,4 0.6

0 0 0 0 0 9.2 41.3 11.8 31.0 6.7

0 0 0 0 0 5.4 22.8 15.6 36.4 19.8

0 0 0.7 1.5 64.l 1.2 20.3 2.6 9.6 0

0 0 0 0 55.9 4.8 23.0 3.2 13.1 0

0 0 0 (I 27.5 13.8 29.9 5.1 23.7 0

0 0 11 0 1.2 20.3 38.2 6.8 33.5 0

(I 0 0 q) 0 156 43.6 6.8 33.9 0. I

0 0 0 0 0 9.4 47.9 7.0 34.5 I. 2

0 0 0 0 0 8.7 41.0 7.5 36.9 5.9

0 0 0 0 0 5.0 21.1 8.7 44.9 20.3

0 0 24.2 36.1 29.5 0.t 0.1 1.8 8.2

0 0 23.2 35.1 30.8 0.1 0.3 1.8 8.7

0 0 20.2 32.6 34.5 0.1 0.9 1.8 9.9

0 0 15. I 27.5 42.4 0.3 1.3 1.8 I 1.6

ii t! 9. I 18.8 53.7 07 19 1.8 14.11

0 0 2.7 8.2 66.9 0.9 3.0 1.8 16.5

0 0 0.3 1.4 73.5 1.4 4.1 2.0 17.3

0 0 0 0 71.6 4.0 4.2 2.4 17.8

Nonwaxy oil reaction network I°C/my heating rate ASPH NSO AROM SAT C6-14 C3 5 C2 BTXN COKE Ct

7.1 17.0 23.2 36.7 15.9 0.1 0 0 0 0

0.2 4.2 25.2 36.7 27.9 0.1 0 1.7 4.0 0

0 0.1 26.0 36.7 30.1 0.t 0 2.4 4.6 0

0 0 24.3 35.3 31.2 0.1 2.1 2.4 4.6 0

0 0 9.2 18.4 51.5 0.2 10.4 2.4 7.9 0

Waxy oil reaction network, 0.5°C/my heating rate ASPH NSO AROM SAT C6 14 C3 5 (?2 BTXN COKE

7.1 17.0 23.2 36.7 15.9 0.1 0 0 0

0.5 6.7 24.4 36.7 24.3 0.1 0 1. I 6.2

0 1.2 24.9 36.7 27.6 0.1 0.1 1.6 7.8

0 0 25.2 36.7 27.9 0.1 0.1 1.8 8.2

0 0 24.9 36.5 28,4 0.1 0.1 1.8 8.2

lar weight of the compounds and compound groups. Then the oil composition is regrouped into C2, C3-5, and C 6 + by removing C1 from the composition. The C6-14 composition is determined by multiplying the C~ 10 (or C6dl) wt % from reservoir fluid analysis by a C6 14/C6 10 (or C6 14/C~lt) ratio derived from whole-oil gas chromatography data. Finally, the C . fraction is divided into SAT, AROM, NSO, and ASPH components by using liquid chromatography data. In cases where reservoir fluid data are not available, the C~5_ fraction determined from oil topping can be subdivided into C3-5 and C6-14 fractions from whole-oil gas chromatography data, and liquid chromatography data are used to determine the composition of SAT, AROM, NSO, and ASPH. PVT calculations indicate that accurate data can still be derived by using this composition for low maturity (low API gravity, low solution gas content) oils. The thermal and burial history of a modeled area is input into PMOD as a thermal history file for the reservoir. Accurate thermal and burial history is very important to the oil cracking modeling. For example, it may help determine whether high paled-heat flow history in the reservoir or late migration from deep, more mature source rock or reservoir(s) is responsible for the presence of abnormally high API gravity oils in shallow reservoirs which have low present-day temperature.

OUTPUT OF THE MULTICOMPONENT

KINETICS MODEL

Several examples of output data were generated to help visualize the relationship between residence time, reservoir temperature, and oil composition during the cracking process. Figure 6 is a three-dimensional view of the API gravity variation as a function of residence time and reservoir temperature for an initial oil of 30 degrees API. Figure 7 shows the change in API gravity with increasing reservoir temperature at a constant residence time of 50 my. This time-slice representation shows that oil cracking is highly dependent upon the initial oil composition for temperatures up to 140°C (285':F). At higher temperatures, the modeled API gravity converges for all oils regardless of initial API gravity. This is to be expected because the difference in initial API gravity is due to differences in concentration of hydrocarbon and nonhydrocarbon components with lower activation energies than C~ fractions, which are only present at higher temperatures. Such data provide a rapid estimation of the minimum API gravity expected for a reservoir in a frontier or mature area. However, detailed oil cracking modeling should be performed for areas with complex geological history. Calculation of the reservoired oil composition as a function of oil cracking reaction network and reservoir thermal history is demonstrated below by three examples. The first example shows the effect of

Modeling preservation and composition of reservoired oils

heating rate on oil cracking in high-temperature reservoirs. In this case, reservoir temperature was initially 100"C and increased linearly at l°C/my or 0.Y'C/my over a period of 140my. The waxy oil reaction network was used for modeling. The results (Table 5, Fig. 8) show that at the high heating rate, resins and asphaltenes are consumed at 25 my and aromatics and saturates are consumed at 75 my after reservoir was charged. The three major episodes of COKE generation correspond to the cracking of

creases initially and then starts to decrease as C2 and BTXN, and later Ci starts to increase significantly. The changes in the GOR of the remaining oil are mainly affected by the changes in the proportion of C3-5 and C2 components. The final remaining oil, which is approx. 20 wt % of the original oil, is composed mainly of stable aromatic compounds (BTXN). The time required to reach a certain degree of cracking is approximately doubled at the low heating rate. For example, AROM and SAT components are consumed, and C6-14 component reaches maximum at 140 my after oil cracking starts.

NSO + ASPH, AROM + SAT, and C6-14 components. The API gravity of the remaining oil in-

Vltr|nlte 1 ;

8 .1 7

reflectance,

percent 3

Z i

ref|ectanee,

qltrlnlte

v

|

I r

0.4( .

.

.

.

.

.

.

.

.

.

.

percent

3 r

2 I .

1~

8.1

919

8.31

8.1

0. Z:

_°e.1

:

ice

80

o

- B.Z|

:

e,e

e. IG

PH

e'e I

--....

e'e'~

e

e.[

"'" '......°

i

58

,

I ell

r

150

•

, ..,,o.

e.ee';

.:....."""

e.'.

i

0,4Q

"

I IB8

58 !

l

"'*,.'-. 158 1

~.3~.e" 3~ e.a~

o

.2 e.

e.1~F

e.

e.l~

e.

e.e~t

• 8E

50

1Be

158

r

50

108

158

4~:

?e ~6e >m5~

i^ 3e3E 2,4

\

4~

280

50

I ilQ Time, My

150

0

50

100 Time,

MSI

Fig. 8. The PMOD output for the compositional, API gravity, and GOR changes as a function of the extent ofoii cracking over a reservoir temperature increase from 100°C at a heating rate of l°C/my (solid curves) and 0.5°C/my (dotted curves) over a 140 my period. The modeling was performed by using the waxy oil reaction network. Percent vitrinite reflectance was calculated by EASY%Re (Sweeney and Burnham, 1990) and corresponds to the l°C/my heating rate (solid curves).

158

920

LUNG-CHUANKUO and G. ERic MICHAEL Vitrln|%e

ref|ectanc~e

1 i

0.1[

V l t r l n | t e r e f | e c t a n c e , percent

percent

2 i

1

3 i

3 1

0.1E

0.3

0.1~

;AT

0.3

0.1~

0. esI

N~

.oo. te

f

o

o.eoI 0.0E

o.z~

\

0.10

0,0

&SPH

0. ~

0,o~

. t

I 100

50

0

0t 0

150

I

-

100

50

0 . 5 E - - -

0.8

150 I

0 , 4 ~,

0.7

0.4~ 0.6 0 . 3=. 0.5

S

° 0.

o

~

~0.4

0. 0.,

0,3

S

0.2

0. 0.

0.1

0.1

0

50

0 00

!

1

f

15e

100

0

50

100

150

54

1

48

A2 m61~

36

~ sol

Nse

g 241 tD

41

/

/

181

f eo I

l

o

so

t 1oo

*~

Time, My

l 0

0

/

L-.--/~-j $0

, *~

Time, M~

Fig. 9. The PMOD output for the compositional, API gravity, and GOR changes as a function of the extent of oil cracking over a reservoir temperature increase from 100°C at a heating rate of 1"C/my over a 140 my period. The nonwaxy oil reaction network was used for the modeling.

The second example demonstrates the effect of reaction network on oil cracking. An initial reservoir temperature of 100°C, a heating rate of l°C/my, and a time of 140my are used. The major differences between the two reaction networks are that the nonwaxy reaction work results in (1) earlier appearance of C2, (2) smaller amount of C3-5 component, and (3) larger amount of C2 and COKE and smaller amount of BTXN at the final stage of cracking (Table 5, Figs 8 and 9). The reservoired oil composition shows greatest difference at 60-110my after cracking; that derived from an originally waxy oil tends to have a lower C2/C3-5 ratio (Table 5). Thus, reaction network mainly afl'eets the composition of

the reservoired oils during the cracking process. Figures 8 and 9 further show that black oils (those containing Cl5 + compounds) are present at maturity levels of 1.4% Ro or below, condensates (which contain mainly C6,4 compounds) are present at 1.4-1.8% Ro, wet gases (those containing mainly C2 compounds) are present at 1.8-3.0% Ro, and dry gases (those containing mainly Ci) are present at 3.0% Ro and above. This is an excellent agreement with the established maturity ranges in which these types of hydrocarbons are expected to be present. The third example compares the oil compositional changes in a 140 my old reservoir with a heating ratc of 0.5°C/my at an initial temperature of 100 C vs

Modeling preservation and composition of reservoired oils 50'C. The results (Fig. 10) show that the effect of lower initial reservoir temperature is similar to that of lower heating rate; both result in slower oil cracking. This example shows that oils accumulated in lowtemperature reservoirs may remain stable for a substantial period of time. In the case of the 50°C initial temperature, the only minor change after 40 my is the small increase in COKE, BTXN, and C6-14 at the expense of ASPH and NSO. After 100 my of accumulation the oil is only 5% cracked with a slight increase in the API gravity from 26 to 32 degrees and an essentially unchanged GOR between 8 and 9 SCF/ STB.

VI t r I O I t e 8.11

TEST AND APPLICATION OF THE MODEL

This section presents a test as well as demonstrates the application of the present model by using field data from the Jurassic Smackover Trend in northern Gulf of Mexico. The nonwaxy oil reaction network was used. The Northern Gulf Trend includes oils from Texas, Louisiana, and Arkansas, and the Southern Gulf Trend includes oils from Mississippi, Alabama, and Florida (Fig. 1 i). The average presentday geothermal gradient is 1.5 and I.l°F/100ft, respectively, in the Northern and Southern Gulf trends. The residence time is estimated at 50 and

percent

rear I e ¢ t a n c f f w

8.8

1.B

1.4

,

i

i

921

VI tr inlte

B.8 I

B.4~

ref

lectence,

percent

1.0 I

1.4 i

I

8.1!

......... ?" ................ "'". "-

NSO

0.1~ 8.1i

o

oo.I .g

.2

..... ,~,"

\

~8.8

8.B

f~ '-" H/" "'"'"'..... -.

8.8

8. B~

~.~ 0 8.

~

I 58

°''''°'°'"",,

I

I 180

1

0.0 I

'"',, 158

B

O. 4 q

i

8.

O. 35F

0.

a.3eF

O.

I

150

lg8

50

I

,

o. 25[-

o

o

-go. 8..:

..°... . . . . . . . . . . .

O.r. f. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

o......,"" °

02

0.1 i 58

8O

188

i

I

a. o ~ / 158

COKE

..'""

50

BTXN

100

158

108

150

!

7E

6OO

~6E

580

498

NsE

g

~9

4E 288

3~

f................ °........... °°

.,°°.,,,..,,.

I 5e

188 i lOB

Time, M~

158

8

58 Tlmet MLj

Fig. 10. The PMOD output for the compositional, API gravity, and GOR changes as a function of the extent of oil cracking from an initial reservoir temperature of 100°C (solid line) and 50°C (dotted line) at a heating rate of 0.5°C/my over a 140 my period. The waxy oil reaction network is used for modeling. Vitrinite reflectance corresponds to the 100°C initial temperature (solid curves).

922

LUNG-CHUANKuo and G. ERICMICHAEL

oKj ....... . . ~ _ __.s. .~.°. ~ nx ;

.-:

i i

~u~o,~

'

\, Northern

Gu f

Trend

*,

,~

.,:~lr~--~-~

¢ "~

TX

,;

Southern

I

Gulf

~'. . . . . . . . . .

~

i

!

"~

"

T r e n d ~ j ~ ~ " 7

~J~~"6 "

Fig. 11. An index map showing the location of the Jurassic Smackover Trend oils discussed in the text (sources: Sofer, 1988; Claypool and Mancini, 1989).

30 my, respectively, for the Northern and Southern Gulf Trends (Sweeney, 1990). The variation in API gravity with depth is attributed primarily to thermal maturation in the reservoir (Sofer, 1988; Claypool and Mancini, 1989). The calculated API gravity was determined from an initial composition of an i 1° API gravity Cretaceous Lower Tuscaloosa oil from Mississippi (Sofer, 1988). It should be kept in mind that the initial prediction of the API (17.7 °) based on the fraction composition of this oil was high because of the high sulfur content of this oil (7.6 wt %), The API prediction with increasing reservoir temperture (and extent of cracking) is considered reasonable because the sulfur content decreases significantly with thermal maturity for oils in this area (Sofer, 1988) as well as in general (Orr, 1986; Manowitz et al., 1991). The predicted minimum API gravity for the Southern Gulf Trend fits most of the data [Fig. 12(A)]. Most of the oils fall slightly to the left of the predicted API trend, indicating that most oils analyzed were expelled from their source rock(s) at slightly higher maturity than the oil used to derive the modeled API trend. Oils which plot to the right of the API gravity trend line may represent oils with shorter residence time (i.e. more recent migration) and/or with different initial composition due to organic facies variation or multiple pulse of expulsion from the source rock. The effect of overpressure present in this area on the geothermal gradient or oil cracking is not taken into account in the model. The present model shows that oil cracking begins around 80°C and reaches approx, 20% by 100°C [Fig. 12(A)]. This temperature for initial oil cracking is lower than that estimated from commonly used models with single component E - A kinetic parameters. For example, an earlier study by Quigley and Mackenzie (1988) used a single activation energy (54.9 kcal/mol) which predicts reasonably well the percent oil cracked at higher temperatures (see their Fig. 8) compared with the present reaction network model. Quigley and Mackenzie (1988) calculated the

percent of oil cracking based on the amount of gas generated instead of the decrease in the amount of oil fractions (such as asphaltenes and resins) at low temperatures. In fact, their data do suggest some low temperature cracking, but it is not taken into account in their model. Thus, the present reaction network model provides more accurate results because it is capable of predicting the composition (API gravity) change of an oil during early cracking ( < 15%) at low reservoir temperatures [Fig. 12(A)]. The early cracking history of an oil is important in recognizing multiple stages of oil migration into shallower reservoirs. Figure 12(B) compares measured G O R data from Claypooi and Mancini (1989) and modeled GOR from the present reaction network. It shows that most observed G O R is slightly higher than the modeled GOR at all reservoir temperatures. This confirms the

Gulf Trend

Southern

9oiA

I°I '0"- Modelled ..,d Data Data I

80 ~0

70 ~ 80 o

i42 "u

/ /

o£ 28 O 21 O 32

50

g.

~ 40 30

@ o_

20 •

I

0

10 l

,

20

I

L

40

L

L

60

I

,

L

,

I

h

I

,

I

L

,

L

80 100 120 14-0 160 180 200

30000 B

o

25000 ~"

20000

~, ~ 15000 "

1ODD0

O 05DO0

0o000

L

,

I

,

I

,

t

,

I

.

I

,

J

•

I

I

I

2o 4o 6o 8o loo 120~40160180200 Reservoir

Temperature

(°C)

Fig, 12. A comparison of the predicted (open circles) and measured (solid circles) API gravity (A) and GOR (B) of the Southern Gulf Trend oils (nonwaxy oil reaction network, 30 my residence time).

Modeling preservation and composition of reservoired oils

Northern Gulf Trend •

90

....O "

Field Data I Modelled Data

,o

70

•

• •

0

a-

l

42

u

120

•

20 i

0

10|1 20

~ I , ] 40 60

•

•

1 2

It.

|

I [ I , i , I , i t I 80 100 120 14-0 160 180 200

Reservoir Temperature (°C) Fig. 13. A comparison of the predicted (open circles) and measured (solid circles) API gravity of the Northern Gulf Trend oils (nonwaxy oil reaction network, 50 my residence time). interpretation that many reservoired oils were expelled from their source at maturity levels higher than the source for the low API gravity oil used for modeling. Fractionation between gas and oil during secondary migration may also account for the deviation of measured GOR to the modeled trend. The Northern Gulf Trend oils also show a general correlation between API gravity and the present-day reservoir temperature, but they plot farther to the left of the predicted API gravity trend (Fig. 13). This may be due to a combination of two factors: (1) the reservoir temperature was higher in the geologic past due to higher paleo-heat flow and/or recent uplift and erosion, and (2) oils plotted were expelled from source rock(s) at different thermal maturity levels. Other factors which cause the measured API gravity variation include variation in original oil composition, secondary processes (e.g. oil mixing, biodegradation, reservoir breaching), and reactions which are not considered in the present model (e.g. thermochemical sulfate reduction, Claypool and Mancini, 1989). This example demonstrates that the present model accurately predicts the minimum API gravity of an oil with a particular composition expected in a given petroleum basin with variable reservoir depths and temperatures.

CONCLUSIONS A muiticomponent oil cracking kinetics model has been developed which provides reasonably accurate estimation of the composition, API gravity, and GOR of oils as a function of the thermal history of the reservoir. This model is flexible and can be

923

applied to both frontier and mature basins. This model may further help identify other secondary alteration processes such as biodegradation and evaporative fractionation in a given petroleum basin. There are several important areas in which our oil cracking modeling can be further improved. First, a comprehensive study is needed to assess the sensitivity of H/C ratio, density, reaction network, input oil composition, and E - A for cracking reactions to the modeling results. Such a study is useful for identifying parameters which require refinement. Second, reaction networks for other types of oils (highsulfur oils in particular) need to be created when high-quality experimental data (such as the IFP data) become available. Finally, theoretical and experimental work is needed to quantify the effect of pressure on oil cracking which is essential for modeling the preservation of oils in deep, overpressured reservoirs. Associate Editor--M. RADKE Acknowledgements--The authors thank Conoco management for permission to publish this work. They appreciate helpful discussions with Larry Van Stone, Tom Ha, and Carolyn Thompson-Rizer (Conoco). The paper has benefittedfrom critical reviews by Alan Burnham and Roger Marzi. The manuscript was prepared by Cindy Larmer. REFERENCES

Atkins P. W. (1978) Physical Chemistry. Freeman, San Francisco. Barth T. and Nielsen S. B. (1993) Estimating kinetic parameters for generation of petroleum and single compounds from hydrous pyrolysis of source rocks. Energy Fuels 7, 100-110. Behar F., Kressmann S., Rudkiewicz J. L. and Vandenbroucke M. (1992) Experimental simulation in a confined system and kinetic modelling of kerogen and oil cracking. In Advances in Organic Geochemistry 1991 (Edited by Eckardt C. B., Larter S. R., Manning D. and Maxwell J. R.). Org, Geochem. 19, 173-189. Pergamon Press, Oxford. Behar F., Ungerer P., Kressmann S. and Rudkiewicz J. L. (1991) Thermal evolution of crude oils in sedimentary basins: experimental simulation in a confined system and kinetic modeling. Rev. Inst. Ft. Pet. 46, 151-181. Benson S. W. (1976) Thermochemical Kinetics, 2nd edition. Wiley, New York. Bianco A. D., Panariti N., Anelli M., Beltrame P. L. and Carniti P. (1993)Thermal cracking of petroleum residues 1. Kinetic analysis of the reaction. Fuel 72, 75-80. Bjor~y M., WilliamsJ. A., Dolcater D. L. and Winters J. C. (1988) Variation in hydrocarbon distribution in artificially matured oils. In Advances in Organic Geochemistry 1987 (Edited by Mattavelli L. and Novelli L.). Org. Geochem. 13, 901-913. Pergamon Press, Oxford. Boudart M. (1968) Kinetics of Chemical Processes. Prentice-Hall, Englewood Cliffs, N.J. Braun R. L. and Burnham A. K, (1990) Mathematical model of oil generation, degradation, and expulsion. Energy Fuels 4, 132-146. Braun R. L. and Burnham A. K. (1992) PMOD: a flexible model of oil and gas generation, cracking, and expulsion. In Advances in Organic Geochemistry 1991 (Edited by Eckardt C. B., Larter S. R., Manning D. and Maxwell J. R.). Org. Geochem. 19, 161-172. Pergamon Press, Oxford. Burnham A. K. and Braun R. L. (1990) Development of a

924

LUNG-CHUAN KtJo and G. ERIC MICHAEL

detailed model of petroleum formation, destruction, and expulsion from lacustrine and marine source rocks. In A&,anves in Organic" Geochemistry 1989 (Edited by Durand B. and Behar F.). Org. Geochem. 16, 27-39. Pergamon Press, Oxford. Claypool G. and Mancini E. A. (1989) Geochemical relationships of petroleum in Mesozoic reservoirs to carbonate source rocks of Jurassic Smackover Formation, southwestern Alabama. AAPG Bull. 73, 904-.-924. Clementz D. M. (1976) Interaction of petroleum heavy ends with montmorillonite. Clay Min. 24, 312 319. Cornelius C. D. (1984) Classification of natural bitumen: a physical and chemical approach. In Exploration for Heavy Crude Oil and Natural Bitumen (Edited by Meyer R. F.), AAPG Studies in Geology # 25, pp. 165 174. AAPG, Tulsa, Okla. Curiale J. A. (1984) Distribution and occurrence of metals in heavy crude oils and solid bitumens--implications for petroleum exploration. In Exploration .for Heavy Crude Oil and Natural Bitumen (Edited by Meyer R. F.), AAPG Studies in Geology #25, pp. 207-219. AAPG, Tulsa, Okla. Curiale J. A. (1986) Origin of solid bitumens, with emphasis on biological marker results. In Advances in Organic Geochemistry 1985 (Edited by Leythaeuser D. and Rullkrtter J.). Org. Geochem. 10, 559 580. Pergamon Press, Oxford. Czarnecka E. and Gillott J. E. (1980) Formation and characterization of clay complexes with bitumen from Athabasca oil sand. Clay Min. 28, 197-203. Domin~ F. (1989) Kinetics of hexane pyrolysis at very high pressures. I. Experimental study. Energy Fuels 3, 89. Domin~ F. (1991) High pressure pyrolysis of n-hexane, 2,4-dimethylpentane and l-phenylbutane. Is pressure an important geochemical parameter? Org. Geochem. 17, 619 634, Domin~ F. and Enguehard F. (1992) Kinetics of hexane pyrolysis at very high pressures---3. Application to geochemical modeling. Org. Geochem. 18, 41 49. England W. A., Mann A. L. and Mann D. M. (1991) Migration from source to trap. In Source and Migration Processes and Evaluation Techniques (Edited by Merrill R. K.), AAPG Treatise of Petroleum Geology, pp. 23--46. AAPG, Tulsa, Okla. Erdman J. G. and Dickie J. P. (1964) Mild thermal alteration of asphaltic crude oils. Am. Chem. Soc. Div. Pet. Chem. Preprints 9, No. 2, B69 B79. Fassihi M. R., Meyers K. O. and Weisbrod K. R. (1985) Thermal alteration of viscous crude oils. SPE 60th Ann. Tech. Conf. Exhib., Las Vegas, Nev., Paper 14225. Geniesse J. C. and Reuter R. (1932) Reaction-velocity constants of oil cracking. Ind. Eng, Chem. 24, 219-222. Hayashitani M., Bennion D. W., Donnely J. K. and Moore R. G. (1978) Thermal cracking models for Athabasca oil sands oil. SPE 53rd Ann. Tech. Conf. Exhib., Nev., Paper 7546. Hayes J. M. (1991) Stability of petroleum. Nature 352, 108-109. Henderson J. H. and Weber L. (1965) Physical upgrading of heavy crude oils by the application of heat. J. Can. Pet. Technol. 4, 206-212. Hesp W. and Rigby D. (1973) The geochemical alteration of hydrocarbons in the presence of water. Erdrl KohleErdgas 26, 70 76. Hillebrand T. and Leythaeuser D. (1992) Reservoir geochemistry of Stockstadt oilfield: compositional heterogeneities reflecting accumulation history and multiple source input. In Advances in Organic" Geochemistry 1991 (Edited by Eckardt C. B., Larter S. R., Manning D. and Maxwell J. R.). Org. Geochem. 19, 119-131. Pergamon Press, Oxford. Hirschberg A. (1984) The role of asphaltenes in compo-

sitional grading of a reservoir's fluid column. SPE 59th Ann. Tech. Conf. Exhib., Houston, Tex., Paper 13171. Horsfield B., Scbenk H. J., Mills N. and WeRe D. H. (1992) An investigation of the in-reservoir conversion of oil to gas: compositional and kinetic findings from closed-system programmed-temperature pyrolysis. In Advances in Organic Geochemistry 1991 (Edited by Eckardt C. B., Larter S. R., Manning D. and Maxwell J. R.). Org. Geochem. 19, 191-204. Pergamon Press, Oxford. Keith P. C., Ward J. T. and Rubin L. C. (1933) The cracking of mid-continent virgin gas oil over a wide range of temperatures and pressures. Am. Pet. Inst. Proc. 14M, 49~37. Koots J. A. and Speight J. G. (1975) Relation of petroleum resins to asphaltenes. Fuel 54, 179-184. Krishna R., Kuchhai Y. K., Sarna G. S. and Singh I. D. (1988) Visbreaking studies on Aghajari long residue. Fuel 67, 379 383. Latter S. and Mills N. (1991) Phase-controlled molecular fractionations in migrating petroleum charges. In Petroleurn Migration (Edited by England W. A. and Fleet A. J.L PP. 137 147. Geological Society Special Publication No. 59, The Geological Society, London. Leythaeuser D., Schaefer R. G. and Radke M. (1988) Geochemical effects of primary migration of petroleum in Kimmeridge source rocks from Brae field area, North Sea. I: gross composition of C,5 +-soluble organic matter and molecular composition of C,5 ~-saturated hydrocarbons. Geochim. Cosmochim. Acta 52, 701-.713. Mackenzie A. S. and Quigley T. M. (1988) Principles of geochemical prospect appraisal. A APG Bull. 72, 399-415. Magaril R. Z. (1973) The Formation of Carbon by Thermal Conversion of Individual Hydro-carbons and Petroleum Products. Chemia, Moscow. Mallinson R. G., Braun R. L., Westbrook C. K. and Burnham A. K. (I 992) Detailed chemical kinetics study of the role of pressure in butane pyrolysis. Ind. Eng. Chem. Res. 31, 3745. Mango F. D (1990) The origin of light hydrocarbons in petroleum: a kinetic test of the steady-state catalytic hypothesis. Geochim. Cosmochim. A cta 54, 1315-1323. Mango F. D. ( 1991) The stability of hydrocarbons under the time temperature condition of petroleum genesis. Nature 352, 146 148. Mango F. C. (1992) Transition metal catalysis in the generation of petroleum and natural gas. Geochim. Cosmochim. Acta 56. 553 555. Manowitz B., Krouse J. R., Barker C. and Premuzie E. T. (1990) Sulfur isotope data analysis of crude oils from the Bolivar Coastal Fields. In Geochemistry of Sulfur in Fossil Fuels (Edited by Orr W. L. and White C. M.), pp. 592 612. American Chemical Society, Washington, D.C. McNab J. G., Smith P. V. Jr and Betts R. L. (1952) The evolution of petroleum. Ind. Eng. Chem. 44, 2556-2563. Meyerhoff A. A. and Meyer R. F. (1984) Geology of heavy crude oil and natural bitumen in the USSR, Mongolia, and China. In Exploration for Heavy Crude Oil and Natural Bitumen (Edited by Meyer R. F.), AAPG Studies in Geology #25, pp. 31 101. AAPG, Tulsa, Okla. Mianowski A. and Radko T. (1992) Evaluation of the solutions of a standard kinetic equation for non-isothermal conditions. Thermochim. Acta 204, 281-293. Monin J. C. and Audibert A. (1988) Thermal cracking of heavy-oil/mineral matrix systems. SPE Reservoir Eng. 3, 1243 1250. Nielsen S. B. and Dahl B. (1991) Confidence limits on kinetic models of primary cracking and implications for the modeling of hydrocarbon generation. Mac. Pet. Geol. g, 483 ~492. Nowak S. and Gunschel H. (1983) Pyrolysis of petroleum liquids: naphthas to crudes. In Pyrolysis, Theory and

Modeling preservation and composition of reservoired oils hulustrial Practice (Edited by Albright L. F. et al.), pp. 277-326. Academic Press, New York. Orr W. L. (1986) Kerogen/asphaltene/sulfur relationships in sulfur-rich Monterey oils. In Advances in Organic Geochemistry 1985 (Edited by Leythaeuser D. and Rullk6tter J.). Org. Geochem. 10, 499-516. Pergamon Press, Oxford. Phillips C. R., Haidar N. I. and Pooh Y. C. (1985) Kinetic models for the thermal cracking of Athabasca bitumen. Fuel 64, 678-691. Price L. C. (1993) Thermal stability of hydrocarbon in nature: limits, evidence, characteristics and possible controls. Geochim. Cosmoehim. Acta 57, 3261-3280. Quigley T. M. and Mackenzie A. S. (1988) The temperature of oil and gas formation in the subsurface. Nature 333, 549-552. Sekhar M. V. and Ternan M. (1979) Pyrolysis of pitch derived from hydrocracked Athabasea bitumen. Fuel 58, 92-98. Shu W. R. and Venkatesan V. N. (1984) Kinetics of thermal visbraking of a Cold Lake bitumen. J. Can. Pet. Technol. 23, 60--64. Sofer Z. (1988) Biomarkers and carbon isotopes of oils in the Jurassic Smackover trend of the Gulf of Mexico. Org. Geochem. 12, 421-432. Sweeney R. E. (1990) Chemical alternation of Smackover oils as a function of maturation. In Gulf Coast Oils and Gases (Edited by Schumacher D. and Perkins B. F.), pp. 23-30. GulfCoast Section, SEPM Foundation, Houston. Sweeney J. J. and Burnham A. K. (1990) Evaluation of a simple model of vitrinite reflectance based on chemical kinetics, AAPG Bull. 74, 1559-1570. Thompson K. F. M. (1987) Fractionated aromatic petroleums and the generation of gas-condensates. Org. Geochem. 11, 573-590. Tippee B. (Ed.) (1990) Oil and Gas Journal Data Book. Penwell, Tulsa. Tissot B. P. and Welte D. H. (1984) Petroleum Formation and Occurrence, 2nd edition. Springer, Berlin.

925

Tissot B. P., Pelet R. and Ungerer Ph. (1987) Thermal history of sedimentary basins, maturation indices, and kinetics of oil and gas generation. AAPG Bull. 71, 1445-1466. Ungerer P. (1990) State of the art of research in kinetic modeling of oil formation and expulsion. In Advances in Organic Geochemistry 1989 (Edited by Durand B. and Behar F.). Org. Geochem. 16, 1-25. Pergamon Press, Oxford. Ungerer P., Behar F. and Discamps D. (1981) Tentative calculation of the overall volume expansion of organic matter during hydrocarbon genesis from geochemistry data. Implications for primary migration. In Advances in Organic Geochemistry 1981 (Edited by Bjor~y M. et al.), pp. 129-135. Wiley, Chichester. Ungerer P., Behar F., Villalba M., Heum O. R. and Audibert A. (1988) Kinetic modeling of oil cracking. In Advances in Organic Geochemistry 1987 (Edited by Mattavelli L. and Novelli L.). Org. Geochem. 13, 857-868. Pergamon Press, Oxford. Von Kopsch H. (1992) Investigations on the influence of pressure to the kinetics of pyrolysis and oxidation reactions by means of DSC. Erd~l Kohle-Erdgas 108, 363-368. Waxman M. H., Deeds C. T. and Closmann P. J. (1980) Thermal alteration of asphaltenes in Peace River tars. SPE Ann. Tech. Conf. Exhib., Paper 9510. Weast R. C. (1985) CRC Handbook o f Chemistry and Physics, 66th edition. CRC Press, Boca Raton, Fla. Welte D. H., Schaefer R. G. and Yalcin M. N. (1988) Gas generation from source rocks: aspects of a quantitative treatment. Chem. Geol. 71, 105-116. Wilhelms A., Larter S. R., Leythaeuser D. and Dypvik H. (1990) Recognition and quantification of the effects of primary migration in a Jurassic clastic source rock from the Norwegian continental shelf. In Advances in Organic Geochemistry 1989 (Edited by Durand B. and Behar F.). Org. Geochem. 16, 103-113. Pergamon Press, Oxford.