Modifications in the Composition of Crude Oils During In Situ

Chapter 22

Modifications in the Composition of Crude Oils During In Situ Combustion

Downloaded by UNIV LAVAL on October 15, 2015 | http://pubs.acs.org Publication Date: July 10, 1989 | doi: 10.1021/bk-1989-0396.ch022

A. Audibert and J . Roucaché Institut Français du Pétrole, B.P. 311, 92506 Rueil-Malmaison, Cedex, France

During enhanced oil recovery by i n - s i t u combustion, crude oil undergoes chemical and physical changes. In in-situ combustion laboratory tests, a i r i n j e c t i o n was stopped to interrupt the reactions. The organic matter sampled ahead of the burnt zone was analyzed using an analytical procedure s p e c i f i c a l l y designed to characterize the evolution of the composition of the crude oil. The coke deposit was characterized by Infrared Spectroscopy and O i l Show Analyzer. The residual oil and the produced oil samples were characterized by SARA Analysis. The interpretation of tests involving crude o i l s with d i f f e r e n t geochemical compositions shows the possible influence of the crude oil composition on the amount of coke deposit and on its a b i l i t y to undergo i n - s i t u combustion. The results which provide valuable information f o r numerical simulation of i n - s i t u combustion, concern not only the coke deposit (amount, composition, oxygen r e a c t i v i t y ) but also the organic matter sampled ahead of the combustion zone (composition, coke precursors) and the produced oil.

During enhanced o i l recovery by i n - s i t u combustion, a crude o i l undergoes chemical changes (pyrolysis reactions) and physical changes ( d i l u t i o n by the cracking products, vaporization and condensation of some f r a c t i o n s ) . Both phenomena are important f o r o i l production : - easier and higher recovery due to the change i n o i l viscosity, - influence of the amount of coke deposit on the propagation of the combustion process. 0097-6156/89A)396-0408$06.00y0 © 1989 American Chemical Society In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


22. A U D I B E R T A N D R O U C A C H E

Composition of Crude Oils

409

The cracking and the low-temperature oxidation of crude o i l s have been studied previously i n order to simulate the thermal transformations of o i l to gas and coke during enhanced o i l recovery (1-6). Other authors characterize the thermal modifications of o i l i n the presence of a vapor phase (7)The objective of this work i s to study the possible influence of the crude o i l composition on the amount of coke deposit and on i t s a b i l i t y to undergo i n - s i t u combustion. Thus, the results would provide valuable information not only for numerical simulation of in-situ combustion but also to define better i t s f i e l d of application. With this aim, f i v e crude o i l s with different compositions were used i n s p e c i f i c laboratory tests that were carried out to characterize the evolution of the crude o i l composition. During tests carried out i n a porous medium representative of a reservoir rock, a i r i n j e c t i o n was stopped to interrupt the reactions. A preliminary investigation has been described previously (8). EXPERIMENTAL Oils properties. Five crude o i l s with d i f f e r e n t geochemical compositions have been studied. The different properties of the o i l s are l i s t e d i n Table I. These o i l s can be c l a s s i f i e d under different categories : . O i l A (Paris Basin) - from a marine o r i g i n which i s already altered and w i l l not be further transformed. . O i l B (Rumania) - from the class of naphtenic-aromatic crude o i l s . This o i l w i l l need only a small quantity of energy to be chemically modified to form l i g h t e r hydrocarbons. . Oils C (Boscan), D (Cerro Negro), E (Athabasca) - from the class of asphaltenic-aromatic crude o i l s , have a high sulfur content. The f i r s t two o i l s coming from carbonate source rocks contain polar compounds consisting of very stable polycyclic aromatics. On the other hand, the l a s t o i l contains aromatics which are less condensed and more reactive. Procedure. The combustion c e l l , which i s 2.1 m long and 20 cm i n diameter and the procedure have been described previously (9)• The fluids produced are regularly sampled during the propagation of the combustion front. The o i l samples are separated and analyzed according to the a n a l y t i c a l procedure detailed i n the next paragraph. The a i r i n j e c t i o n i s generally stopped when the combustion front has propagated along the f i r s t half of the length of the porous medium. After a complete cooling of the combustion c e l l under rotation, samples are taken at different points of the porous medium, generally at each thermocouple and at half distance between two successive thermocouples. A l l the coke zone which i s observed downstream from the combustion front i s sampled.

In Oil-Field Chemistry; Borchardt, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1989.


J

P ~ u

|1007 (15°C) 7092 (60°C)|

|1000 (20°C) 2150 (50°C)|

D

E

32.1 36.5

17-3

21.5

1

|

|

43.0

15.5 (210*)

11005 (1S°C) 1300 (60°C)|

C

B

40 (30°C)|

|

| 890 (1S°C)

A

23.6

Aromatics |

47.4

1 Saturates | %

| 960 (20°C) 2000 (18°C)|

mPa.S

1

kg/m

34

1 1

55.2

Oil

TABLE I - OIL PROPERTIES

1 1

36.8 30.8

8.1

13.8

12.0

|

29.5

0.3 1

28.8

|

|

|

1

4.3

4

5.3

0.2

0.3

|

0.1

1

Sulfur % wt

|Asphaltenes| 1 % 1

10.7

%

Resins


22. AUDIBERT AND ROUCACHE


411


A n a l y t i c a l procedure. An a n a l y t i c a l procedure ( F i g . 1) has been improved to characterize both the residual organic matter i n the sands and the o i l recovered during the tests. For example, the analysis of samples by the O i l Show Analyzer (OSA, IFP Fina process, commercialized by Delsi Instruments-France) gives the organic content of rocks (10) and permits the study of the evolution i n the o i l composition. This analysis ( F i g . 2) i s based on a two-step procedure involving successively (a) pyrolysis from ambient temperature up to 600°C, and (b) combustion i n a i r at 600°C. The f i r s t peak corresponds to the detection of the gaseous hydrocarbons up to C_, v o l a t i l i z e d at about 90°C during 2 minutes (gas amount SO i n g/100 g of rock), the following to the l i q u i d hydrocarbons, v o l a t i l i z e d at 300°C during 3 minutes ( o i l amount SI); the hydrocarbons released during the cracking of the residual organic matter from 300°C to 600°C form the peak S2. The detection of the C0 produced by combustion i n a i r at 600°C during 5 minutes of the previously pyrolyzed sample leads to the peak S4 and allows the residual organic carbon content to be determined. The d i f f e r e n t product contents are generally given i n g per 100 g of rock. Here, the different product contents are also given versus the t o t a l carbon content (for example S0/S0+S1+S2+S4) to eliminate the effect of o i l saturation. The o i l extracted from the sand samples or the produced o i l i s studied by thin layer chromatography, which gives the d i s t r i b u t i o n of the different structural groups : saturates, aromatics, resins, asphaltenes (SARA). I f changes are observed i n the o i l composition, the different fractions are further analyzed by gas chromatography on c a p i l l a r y columns with a s p e c i f i c detector f o r each group (Flame i o n i s a t i o n detector f o r aromatics, flame photometry detector f o r thiophenic compounds and thermoionic s p e c i f i c detector f o r nitrogen compounds). After extraction of the l i q u i d o i l phase, the residual organic matter i s isolated from the mineral phase by acid attack (HCl/HF), i n a nitrogen atmosphere at 70°C (11). The residual organic matter i s then characterized by elemental analysis and infrared spectroscopy. 2

RESULTS The porous medium properties f o r the different tests are presented i n Table I I . The tests are carried out i n a porous medium constituted of s i l i c a sand, kaolinite (4%), mixed with heavy crude o i l and water. Analysis of the residual organic matter by O i l Show Analyzer. The evolution i n the composition of the residual organic matter i s studied by OSA i n the coke zone and i n a l l the zone ahead of the combustion front. Whatever the o i l , i n each sand sample, the amount of gaseous hydrocarbons (SO) i s low because a l l the l i g h t hydrocarbons have been stripped by the gas flow. For o i l A, ahead of the coke zone, the amount of organic carbon i n S0+S1+S2 has decreased from 6 g/100 g of rock ( i n i t i a l amount i n the porous medium) to 3 g/100 g. The higher decrease can


OIL-FIELD CHEMISTRY

412

ANALYTICAL PROCEDURE

RECOVERED

OIL SHOW ANALYZER

SAMPLES

OIL

DISTILLATION FRACTION t

ORGANIC

2I0°C


SOLVENT WASHED

Elimination of the free sulphur

DISTILLATE $

EXTRACT

210°

ROCK

HCI/HF leaching

I

I

INSOLUBLE

ORGANIC

MATTER

PRECIPITATION ASPHALTENES (nC ) 7

ELEMENTAL ANALYSIS

INFRARED \

ASPHALTENES

ELEMENTAL ANALYSIS

TLC CHROMATOGRAPHY \SATURATED HYDROCARBONS I

I AROMATIC COMPOUNDSX

ELEMENTAL ANALYSIS

GLASS CAPILLARY GC

AROMATIC COMPOUNDS

THIOPHENIC COMPOUNDS

GLASS CAPILLARY GC

NITROGEN COMPOUNDS

Figure 1. Analytical procedure. (Reproduced with permission from ref. 8. Copyright 1984 Institut Francais du Petrole.)

TABLE II - POROUS MEDIUM PROPERTIES Oil "So fo Sw % O i l content kg/cnr

Air requirement Nm /m Front temperature °C % burned J

57.1 35-4

50.5 20.1

167.4

172.7

57^~

54.4 25.1

5ST4 26.7

-

26.5 203.4

209.5

427

376

207.3 212

298 393

J

450-470

450-500

510-750

635-750

10.2

11.8

19.5

19.3

660-750 16.7





413

AFTER OXIDATION

FREE HC

Figure 2. OSA diagram. (Reproduced with permission from ref. 8. Copyright 1984 Institut Francais du Petrole.)


414

OIL-FIELD CHEMISTRY


be observed for S 2 which corresponds to the content of heavycomponents released from 300 to 600°C. Just ahead of the coke zone, there i s an increase i n the r a t i o S 1 / S 2 with respect to the i n i t i a l o i l . This i s due to the presence of l i q u i d hydrocarbons which have been formed by cracking of heavier hydrocarbons or have been swept by the combustion gases. The same cracking effect i s observed for the other o i l s B to E but on the contrary, the amount of organic carbon i n S 0 + S 1 + S 2 i s equal or even higher than the o r i g i n a l one. Thus, a l l the zone ahead of the coke zone has been enriched by the cracking products but the heavy product content ( S 2 ) remains also high. An example of the progressive changes of the organic matter properties due to the combustion can be observed on F i g . 3 for OIL E . The coke zone and the zone ahead of the coke where the changes are noticeable have been s p e c i a l l y studied. Analysis of the coke zone The amount of the residual organic matter i s given i n Table III for different samples studied. The material balance i s consistent with the results obtained by OSA (S2+S4 i n g/100 g ) . For o i l A, the coke zone i s very narrow and the coke content i s very low (Table I I I ) . On the contrary, for a l l the other o i l s , the coke content reaches higher values such as 4.3 g/ 100 g ( o i l B), 2.3 g/100 g ( o i l C ) , 2.5 g/100 g ( o i l D), 2.4/100 g ( o i l E ) . These organic residues have been studied by infrared spectroscopy and elemental analysis to compare their compositions. The areas of the bands c h a r a c t e r i s t i c of C-H bands (3000-2720 cm ), C=C bands (1820-1500 cm ) have been measured. Examples of results are given i n F i g . 4 and 5 for o i l s A and B. An increase of the temperature i n the porous medium induces a decrease i n the atomic H/C r a t i o , which i s always lower than 1.1, whatever the o i l (Table I I I ) . Similar values have been obtained i n pyrolysis studies (4). Simultaneously to the H/C r a t i o decrease, the bands characteristics of CH^ and CH- groups progressively disappear. The absorbance of the aromatic C-n bands also decreases. This reflects the transformation by pyrolysis of the heavy residue into an aromatic product which becomes more and more condensed. Depending on the oxygen consumption at the combustion front, the atomic 0/C r a t i o may be comprised between 0.1 and 0.3« Analysis of the zone ahead of the coke zone. In this zone, the quantity of extracted o i l i s generally sufficient to obtain the d i s t r i b u t i o n of the different structural groups (SARA analysis) except for o i l A ( F i g . 6 to 9). For o i l B ( F i g . 6), for the f i r s t two samples, the amount of extracted products i s too low and the analysis i s uncertain. It can only be noticed that the asphaltene content i s n u l l . On the contrary, just beyond the coke zone (samples I I I - I V ) , the asphaltene content respectively reaches 12.9 and S*A% whereas the asphaltene content of the i n i t i a l o i l i s only 0.3$. This effect i s also observed for o i l C (10$ versus 6.3%) (Fig. 7), D (24$ versus 13-8$) ( F i g . 8), E (24-4$ versus 8.1$) (Fig. 9). For a l l the o i l s , the amount of resins+asphaltenes generally remains constant and the amount of saturates increases


Composition ofCrude Oils



Figure 3. Analysis by OSA of samples taken in the porous medium for Oil E.


415


|

VII

-

-

0.096

-

0.92

2.06 0.134

1

0.65

4.27 0.15

1-59

1.05

D

-

0.094

0.048

1.49

1 1.1

2.17

2.37

2.51

(1)

0.4

0.35

0.34

(2)

0.194 0.8

| 0.082

1

c

2.27

| 0.22

1

1

0.5

(1)

| 2.1

1 1

3-52

(2)

-

B

0.103

(1)

(1) amount of residual organic matter i n g/100 g of rock. (2) H/C r a t i o determined by elemental analysis.

|

VI

-

1.15

0.4

-

|

IV

0.7

0.7

0.95

|

III

0.55

0.79

(2) 0.75

A

1.02

(1)

I 0.35

1

II

v

|

I

Sample nb|

TABLE I I I - COKE PROPERTIES

-

-

1.48

2.39

O.58 0.6

1.9

1.96

(1)

0.4

0.31

(2)


E

-

0.63

0.5

0.42

0.32

(2)

53

I

r

o

4t




Figure 4. Analysis of the coke zone for Oil A.


417

OIL-FIELD CHEMISTRY


418

Figure 5. Analysis of the coke zone for Oil B.



COMPOSITION

Composition ofCrude Oils

OF THE EXTRACT

419

OIL B

100%-

SATURATES

'OO


AROMATICS

RESINS 0,3%

.ASPHALTENES INITIAL OIL

HI

IE

2E

Figure 6. SARA analysis of extracted oil for Oil B.

COMPOSITION OF THE

EXTRACT

OIL C

100%

SATURATES

AROMATICS

RESINS

ASPI'.^TENES

Figure 7. SARA analysis of extracted oil for Oil C.


420

OIL-FIELD CHEMISTRY

COMPOSITION

OF T H E EXTRACT

OIL D

SATURATES


AROMATICS

RESINS

ASPHALTENES

Figure 8. SARA analysis of extracted oil for Oil D. COMPOSITION O F T H E E X T R A C T

INITIAL OIL

1

I

21

M

OIL E

II

Figure 9. SARA analysis of extracted oil for Oil E. (Reproduced with permission from ref. 8. Copyright 1984 Institut Francais du Petrole.)




421

whereas there i s a s l i g h t decrease i n the aromatic content. For example, for o i l C, the C c - C « saturate content increases from 37-9$ ( i n i t i a l value) to 58.7$ (sample IV). Ahead of t h i s zone, the o i l extracted from the porous medium progressively recovers i t s i n i t i a l properties. 1

0

Analysis of the recovered o i l . The o i l recovered i s f i r s t d i s t i l l e d . For o i l A, the f r a c t i o n having a b o i l i n g point lower than 210°C at atmospheric pressure (210~ or C~ fraction) represents 2.6 to 11% of the recovered o i l , whereas the i n i t i a l o i l contains 2.5$ of this f r a c t i o n . The chemical changes affecting the produced o i l are consistent with the evolution of i t s physical properties ( F i g . 10). The same effect can be ^observed for a heavier crude. For example, for o i l E, the 210"" f r a c t i o n represents 10 to 15% of the recovered o i l even though this f r a c t i o n doesn't exist i n the i n i t i a l crude o i l . The variations i n the composition of the f r a c t i o n having a b o i l i n g point higher than 210°C (210 ) depend strongly on the i n i t i a l composition of the o i l . For o i l A, s l i g h t differences i n composition exist; the aromatic and r e s i n fractions hardly decrease to form l i g h t e r saturate compounds. The effects are quite similar to those on o i l B whose global composition does not change. But i n the saturate f r a c t i o n , the amount of n and i s o alkanes i s three times higher i n the recovered samples than i n the i n i t i a l one ( F i g . 11). For crude o i l s C and D, some l i g h t e r hydrocarbons are formed during the cracking reactions but the composition of the 210 f r a c t i o n i s hardly modified. In p a r t i c u l a r , i t can be noticed that the asphaltene contents of both of the recovered o i l s remain high. On the contrary, for o i l E the quantity of asphaltenes decreases from 8.1% for the i n i t i a l crude o i l to 4*1% f o r the sample produced at the end of the test ( F i g . 12). Moreover, the amounts of resins + asphaltenes decreases whereas the amounts of saturates and aromatics increase (51.4$ i n the i n i t i a l o i l , 72.4$ for a sample recovered at t = 24 h). The analysis by GC shows that each o i l f r a c t i o n i s enriched i n components with molecular chains ranging from 15 to 30 carbons which don't exist i n the i n i t i a l o i l (n-alkanes, aromatics O^-C^C) ^complex than the initial ones, thiophemc compounds C -C ). The elemental 10 O composition of the asphaltene f r a c t i o n of the samples recovered during the test are shown i n Table IV. There i s an high increase i n the oxygen/carbon r a t i o compared to the s l i g h t decrease i n the hydrogen/carbon r a t i o . The results of the analysis of the resin f r a c t i o n are quite similar. The thermal cracking of the o i l induces the formation of l i g h t e r molecular weight compounds and of a polar denser residue. Those results are consistent with the observations of a f i e l d study (12).


2

w

n

i

c

n

a r e

ess

1 C

9 C

CONCLUSIONS Elemental analysis characterization of

and the

infrared spectroscopy coke deposit. From one

give crude

a good o i l to


OIL-FIELD CHEMISTRY

422

PHYSICAL PROPERTIES OF THE RECOVERED OIL -OIL A % , Recovery /^g/cm (

)

0

m Pa .S

C

—


2

3

Figure 10. Characterization of the recovered oil for Oil A.




423

GC OF SATURATES

INITIAL OIL


- Cai ^on Nb •

OIL

RECOVERED

AT

T=46h

Carbon Nb •

Figure 11. Saturates chromatography for a sample recovered at 46 h of test, compared to the initial one for Oil B.

COMPOSITION

OF THE RECOVERED OIL

OIL E

100%-,

SATURATES

C?OD

m

oOP.

m

50-

W

AROMATICS

i RESINS ASPHALTENES INITIAL OIL

17H30

20H45

24H

31H10

34H10

40 H

Figure 12. SARA analysis of the recovered oil for Oil E.


OIL-FIELD CHEMISTRY

424

TABLE IV - ELEMENTAL ANALYSIS OF ASPHALTENES IN THE RECOVERED SAMPLES - OIL E -

1


I Initial | | Sample recovered at t= | 1 17h30 J 1 20h45 1 1 24h | I 28h | 1 31hlO | 1 34hlO | 1 40h |

H/C

o/c

1.21

|

0.028

|

1.12 1.15 1.16 1.16 1.17 1.16 1.12

1 1 1 1 1 | |

0.144 0.137 0.054 0.133 0.053 0.052 0.048

1 1 1 1 |

another, the amount of coke i s quite d i f f e r e n t , the highest amounts of coke being obtained from the heaviest crude o i l s , and especially those which contain more reactive compounds. For a l l the o i l s , the evolution of the coke composition versus the temperature evolution i s similar; for example, the H/C r a t i o i s generally comprised between 0 . 5 and 0 . 6 for a temperature equal to 400°C. The lowest H/C values ( i . e . lower than 0 . 4 ) are observed for the highest temperatures of the combustion front ( i . e . higher than 500°C). It means that the coke composition can be related to the temperature reached i n the porous medium and i t s amount to the o i l thermal r e a c t i v i t y which i s influenced by the o i l geochemical composition. As the sampling moves downstream from the coke zone, i t may be noticed that whatever the o i l composition, - the f i r s t samples contain the highest amount of residual carbon and no asphaltenes i n the extracted f r a c t i o n of the sample, - i n the following samples having a lower residual carbon content, the extracted o i l contains a higher asphaltene content than the i n i t i a l o i l . This effect i s observed even i f the i n i t i a l asphaltene content of the o i l i s quite n u l l . It seems that the coke formation can be written as the following balance : Aromatics — • Resins — • Asphaltenes — • coke where the r e s i n + asphaltene content remains constant and asphaltenes are the main precursors of coke. The same observations have been made i n low-temperature oxidation experiments ( 6 ) . Whatever the o i l composition, the cracking reactions enhance the amount of the 210~ f r a c t i o n i n the recovered o i l . The composition of the 210 f r a c t i o n depends on the i n i t i a l o i l composition : i t i s not modified i f the o i l i s already altered or i f the o i l contains very stable compounds. This experimental work gives data that help us to understand the mechanisms of coke formation during i n - s i t u combustion. Moreover, i n case of a f i e l d application, a study of the o i l produced and the organic matter from cores taken behind the combustion front, related to the analysis of the i n i t i a l o i l could provide information on the propagation of the combustion front.




425

REFERENCES 1.

2.

3.

Fassihi, M.R., Meyers, K.O., Weisbrod, K.R., "Thermal Alteration of Viscous Crude O i l s " , Annu. Fall Meeting of Soc. Petroleum Engrs, SPE paper No 14225 (Sept. 1985). Ungerer, P., Béhar, F., V i l l a l b a , M., Heum, O.R., Audibert, A., "Kinetic Modelling of O i l Cracking". 13th Internation. Meeting on Organic Geochem., Venice (Sept. 1987). Béhar, F., Audibert, A., V i l l a l b a , M., "Secondary Cracking of Crude o i l s : Experimental Study" - Submitted to Energy and

Fuel (1988). 4.

Abu Khamsin, S.A., Brigham, W.E., Ramey, H.J., "Reaction Kinetics of f u e l formation for i n - s i t u combustion", F i t h Soc Petroleum Engrs Middle East Show, SPE paper No 15736 (March

5.

Millour, J.P., Moore, R.G., Bennion, D.W., Ursenbach, M.G., Gie, D.N., "A simple Implicit Model for Thermal Cracking of Crude O i l s " , Annu. F a l l Meeting of Soc. Petroleum Engrs, SPE Paper No 14226 (Sept. 1985). Millour, J.P., Moore, R.G., Bennion, D.W., Ursenbach, M.G., Gie, D.N., "An Expanded Compositional Model for Low Temperature Oxidation of Athabasca Bitumen". J . Canad.


1987)

6.

Petroleum Technol., (May-June 1987), p. 24-32. 7.

Monin, J.C., Audibert, A., "Thermal Cracking of Heavy Oil/Mineral Matrix Systems", Soc. Petroleum Engrs, Internation. Symp. on O i l f i e l d Chemistry, SPE paper No 16269,

8.

Audibert, A., Roucaché, J . , "Evolution of the Composition of a Crude O i l During I n - s i t u Combustion", Characterization of Heavy Crude Oils and Petroleum Residues. Ed. Technip, Paris, p

9.

Burger, J . , Sourieau, P., Combarnous, M., "Thermal Methods of O i l Recovery", Ed. Technip, Paris and Gulf Publishing Company, Houston (1985). E s p i t a l i é , J . , Marquis, F., Barsony, J . , "Geochemical Logging by the O i l Show Analyzer" A n a l y t i c a l Pyrolysis - Techniques et Applications - Voorhees, Ed. Butterworth, Londres, (1984). Durand, B., "Kerogen", Ed. Technip, Paris (198O). Bojes, J.M., Wright, G.B., "Application of F l u i d Analyses to the Operation of an i n - s i t u Combustion P i l o t " . Annu. Technical Meeting of Petroleum Soc. of CIM, Paper No 86-37-61, (June 1986).

(Feb. 1987).

135-139, (1984).

10.

11. 12.

R E C E I V E D November 28,1988


Modifications in the Composition of Crude Oils During In Situ

Recommend Documents