fuel 2005 (3)

8/12/2019 fuel 2005 (3)

1/10

FTIR and SUVF spectroscopy as an alternative method in reservoirstudies. Application to Western Mediterranean oils

A. Permanyera,*, L. Douifib, N. Dupuyb, A. Lahcinia, J. Kisterb

aUniversitat de Barcelona, Facultat de Geologia, Dt. de Geoqu mica, Petrologia i Prospeccio Geologica, Marti Franques, s/n., 08028 Barcelona, Spain

bFacultedes Sciences et Techniques de St. Jerome, UniversitedAix-Marseille III, CNRS UMR 6171, Systemes Chimiques Complexes,

Laboratoire de Geochimie Organique Analytique et Environnement (GOAE), Case 561, 13397 Marseille cedex 20, France

Received 14 April 2004; accepted 23 June 2004

Available online 7 August 2004

Abstract

Reservoir geochemistry assessment has traditionally used the gas chromatogram fingerprint method and star diagrams. Recently we tested

alternative techniques, such as Fourier transform infra red (FTIR) and synchronous ultra violet fluorescence (SUVF) spectroscopy to

optimise the evaluation of reservoir continuities, and to characterize the geochemical evolution of oils from individual reservoirs. We used

some Western Mediterranean oils to demonstrate that these independent techniques provide results that are in good agreement with each

other. GC fingerprints, FTIR and SUVF spectroscopy can describe the oil characteristics and its evolution in the reservoir. We also show that

some FTIR parameters can be closely related to the API degree.

q 2004 Elsevier Ltd. All rights reserved.

Keywords: Reservoir geochemistry; Fourier transform infra red spectroscopy; Synchronous ultra violet fluorescence; Gas chromatography; Mass spectrometry;

Western Mediterranean; Offshore Spain

1. Introduction

The role of organic geochemistry in the petroleum

industry has been overwhelmingly geared towards

exploration [1]. It has now become apparent that

petroleum geochemistry can play a key role in petroleum

exploration appraisal and development [2].

Geochemistry of reservoirs is well documented in the

literature with most of the studies focusing on characteriza-

tion of oils to solve problems, such as vertical and lateral

reservoir continuities[37].

Heterogeneities in petroleum populations may be used

laterally and vertically for early identification of reservoir

compartmentalization. Indeed, structural and functional

composition of crude oils may be affected by reservoir

compartmentalization. Gas chromatography fingerprints of

oils are extensively employed to detect changes in

composition linked to reservoir connectivity. Star diagrams

using selected inter n-alkanes peak ratios identifiable on a

whole oil chromatogram are currently employed.

However, differences in oils cannot always be deduced by

employing only chromatographic fingerprints and

therefore a new complementary method has been proposed

[8,9].This procedure is based on the Fourier transform infra

red (FTIR) and on synchronous ultra violet fluorescence

(SUVF) spectroscopy. These techniques give reliableinformation such as total concentration of aromatic

compounds or condensation degree of polyaromatic

compounds.

The m ain aim of this paper is to demonstrate

the capability of the FTIR and SUV F for use as

complementary methods to the GC fingerprint method in

reservoir geochemistry. The second goal is to develop an

alternative method to the API degree technique to determine

the maturity degree of oils.

0016-2361/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.

doi:10.1016/j.fuel.2004.06.027

Fuel 84 (2005) 159168

www.fuelfirst.com

* Corresponding author. Tel.: C34-934021416; fax: C34-934021340.

E-mail addresses: [email protected] (A. Permanyer), jacky.

[email protected] (J. Kister).
http://www.fuelfirst.com/http://www.fuelfirst.com/

8/12/2019 fuel 2005 (3)

2/10

2. Geological setting and samples

Western Mediterranean oil fields are located offshore of

the Ebro delta (NE Spain) and were explored and produced

mainly between 1970s and 1990s (Fig. 1). Significant papers

have been published by several authors, who highlighted

both geological and geochemical features[1015].

Mesozoic karstified carbonate rocks, as well as Miocene

dolomites mainly constitute the reservoirs. The Mesozoic

rocks form a horst-graben rift system, where highs make up

Fig. 1. Location map of oil fields of the Western Mediterranean. The Casablanca, Boqueron and Rodaballo are the most important fields currently in

production.

A. Permanyer et al. / Fuel 84 (2005) 159168160

8/12/2019 fuel 2005 (3)

3/10

the main reservoir structures sealed by a thick Pliocene to

Pleistocene series [1517]. The oils from the Casablanca

field are reservoired in Jurassic karstified carbonates, which

constitute the major structure in the area. The Boqueron and

Rodaballo fields consist of single Mesozoic highs and are

separated from each other and from the Casablanca structure.

The Casablanca field produces at wells 8 and 11, situatedin the northern and southern parts of the main structure,

respectively. The Boqueron and Rodaballo fields produce at

their respective wells. Reservoir top depths increase from

Casablanca to Rodaballo fields (25503380 m, respectively).

The origin of the studied oils is assumed to be a tertiary

source rock, which presumably consists of marine shales

deposited in an anoxic environment since the early Miocene

[12]. Lateral variations in source rock facies may occur

locally and should be considered.

3. Experimental

3.1. Gas chromatography and gas chromatographymass

spectrometry

Whole oils were analysed by gas chromatography

(GC) and chromatograms were compared. The 19 minor

interparaffin peak ratios, from C7 to C13 alkanes

were selected (Fig. 2) and the peak height ratios were

plotted on star diagrams to establish similarities or

dissimilarities between the oils. Some classic ratios such

as Pr/Ph, Pr/nC17 and Ph/nC18 were also reported

and plotted together with the peaks selected before

(Fig. 10).Saturated hydrocarbons were also analysed by gas

chromatography/mass spectrometry (GC/MS) to identify

the significant oil features and biomarkers.

3.2. FTIR analysis

The spectrometer used for the FTIR analysis was a

Nicolet Protege-460 coupled to a Nicolet Nic-Plan IR

microscope. Oil samples were analysed by transmission on a

potassium bromide (KBr) thin plate. The film thickness was

about 20mm. A recording between 4000 and 400 cmK1 was

made with the KBr thin plate alone (reference acquisition)and then with the sample. Spectra were recorded with

64 scans and 2 cmK1 resolution.

For each sample, preparation and data acquisition were

performed three times. All the spectra were normalised for

comparison [18]. The main IR bands were determined

Fig. 2. Gas chromatogram fingerprints showing the peaks chosen for constructed star diagrams.

A. Permanyer et al. / Fuel 84 (2005) 159168 161

8/12/2019 fuel 2005 (3)

4/10

thanks to indexes which had been described in

earlier studies[19]. These indexes were used to determineand compare the chemical composition of each sample.

Assignments of the main IR bands were determined by

reference to an earlier work [20]. A deconvolution

technique was applied to increase spectral resolution of

overlapping infrared bands[18]. The main assignments of

the FTIR bands used in this study are described in Fig. 3

and the applied indexes are defined as:

Aliphatic index: (A1460CA1376)/P

A

The sum of the areaP

Arepresents:

XAZ

A1700 CA1600 CA1460CA1376 CA1030 CA864

CA814 CA743 CA724 CA2953;2923;2862;

which is equivalent inFig. 3to

XAZA1CA2CA3CA4CA6CA8CA9CA10

CA11CA12CA13CA14

Aromaticity index: A1600/P

Aaro, (A2/A9CA10CA11

inFig. 3)

Long chains index: A724/(A1460CA1376), (A11/A3CA4

inFig. 3) Substitution 1 index:A864/A864CA814CA743 Substitution 2 index:A814/A864CA814CA743.

The most accurate ratios of these indexes were finally

applied for reservoir compartmentalization and oil maturity

evaluation.

3.3. Synchronous ultra violet fluorescence analyses

Fluorescence measurements were carried out using a

PerkinElmer LS50B luminescence spectrometer.

The wavelength (Dl) interval between lex and lem was

constant and equal to 23 nm. One centimetre thick quartzcells were used.

Fluorescence intensity is related to the quantity of

aromatic compounds present in the sample. It also depends

on various parameters such as temperature, sample

concentration and the kind of solvent [21]. The concen-

tration of 10 mg lK1 was chosen to obtain a suitable signal/

noise ratio of the spectrum. The crude oils were dissolved in

tetrahydrofurane (THF). The THF solvent and the high

dilution used reduced fluorescence-quenching effects.

The analysis of UV fluorescence spectra of standard

polycyclic aromatic hydrocarbons, which are present in

crude oils, allows us to define three main regions A1, A2and A3 (Fig. 4). Each of these spectral regions is

characterized by the number of condensed aromatic

rings, yielding qualitative information on the nature of

the aromatic species present in oils (spectral region from

280 to 580 nm)[22]. The fluorescence index (A2/A1 ratio)

represents the ratio of the aromatic compounds with

three or four rings with respect to the compounds with

two rings. The A3 represents aromatic condensation

with five or more aromatic rings.

Fig. 3. FTIR spectrum of a crude oil between 4000 and 400 cmK1. Band areas measured from valley to valley.

Fig. 4. Synchronous UV fluorescence spectrum of polycyclic aromatic

hydrocarbons present in crude oils. Each spectral region is characterized

by the number of condensed aromatic rings: A1 (two rings), A2

(three or four rings), A3 (five rings or more). (THF, tetrahydrofurane

solution).


8/12/2019 fuel 2005 (3)

5/10

4. Results and discussion

4.1. Geochemical characteristics

Table 1 summarizes the main geochemical parameters

along with global data from the analysed oils.

All samples have similar characteristics, with somedifferences (Table 1). Gas chromatograms show a similar

distribution of n-alkanes, as well as pristane and phytane

isoprenoids, and a minor decrease in nC28C in the

Rodaballo oil (Fig. 5).

Tricyclic terpanes are similar in the two Casablanca oils

(Fig. 6). By contrast, the Boqueron and Rodaballo oils show

dissimilarities between the epimers R and S in the C26 and

C28 tricyclics, and a clear diminution in the C24 tetracyclic

in the Boqueron crude. The C24 tetracyclic is absent in the

Rodaballo oil.

These particularities could be related to discrete

variations in the source rock sedimentary environment,which would be supported by the variation in Ts(18a (H)-trisnorneohopane) in Boqueron and Rodaballo

with respect to the Casablanca oils, and Ts/Tminversed ratio

in the Boqueron oil (Fig. 6). The C24/C23 tricyclic ratio

shows similar values in the Casablanca oils, and higher

values in the Boqueron and Rodaballo oils, thus suggesting

a predominantly shaly environment (Fig. 7).

Pentacyclic terpanes are practically identical in the two

Casablanca samples. The Boqueron crude shows a

diminution in homohopanes (C31C35) homologues. This

diminution is more marked in the Rodaballo oil

(quasi absence of homohopanes as well as Ts and Tm)

(Fig. 6). Tertiary origin for all oils is supported by the

presence of oleanane, which is related to angiosperms[23].

The C27, C28, C29 regular sterane distribution (Fig. 8)

is very similar for all the samples, and is consistent with the

marine origin of source rock. Steranes show a quantitative

diminution from the Casablanca to Boqueron and Rodaballo

oils (Fig. 9). The isotope signature of the four oils is similar,suggesting that they originated from the same source rock

(Table 1).

4.2. GC fingerprints

Three groups of oils are identified when peak ratios are

plotted in star diagrams (Fig. 10). The two oils from

Casablanca compose the first group, indicating very

close ratios, with only one discrete dissimilar ratio

(ratio number 11). This result shows that the Casablanca

crude presents good homogenization across the field

structure, and behaves as a single reservoir compartment.

The Boqueron and Rodaballo oils form two distinct

groups. These two oils present star diagrams that differ from

each other and from that of the Casablanca oils. This finding

clearly shows that the oils belong to different field structures

and m ust therefore be regarded as independent

compartments.

The results obtained by GC fingerprints are consistent

with the geological structures of the fields in this area.

This case constitutes a good example for testing the

application of FTIR and UV techniques in reservoir

evaluation.

Table 1

Geochemical data and parameters of the studied oils

Sample CASABLANCA-8 CASABLANCA-11 BOQUERON RODABALLO

Depth of reservoir (m) G2450 2555 2997 3388

8API gravity 32.2 35.3 38.7 41.3

d13C Saturate HC () 20.55 20.45 20.2 19.5

d13C Aromatic HC () 19.65 19.30 18.30 17.75

% Ro equ.Z0.487*(C29aa20S/aa20R)C0.33 0.74 0.78 0.80 1.03

Moretane/hopane (C30) 0.12 0.11 0.10 0.00

Homohopane index 0.07 0.07 0.09 0.00

Gammacerane indexZGamm/C30HOP 1.71 1.82 2.18 0.00

Oleanane indexZOLN/C30 HOP 0.21 0.27 0.47 1.07

C33 22SC22R/C34 22SC22R 1.90 1.85 2.03 n.d.

Diahopane/C30 hopane 0.03 0.04 0.10 0.26C21/C23 Tricyclic terpanes 0.53 0.54 0.61 0.84

C26/C25 Tricyclic terpanes 0.85 0.88 0.95 1.14

C24/C23 Tricyclic terpanes 0.63 0.65 0.73 0.58

2829 Tric/(TricCC2933 Hop) 0.07 0.09 0.15 0.23PC19C30 Tric/S C29C35 Hop 0.35 0.50 1.18 5.79

% C27 sterane 30.91 28.36 32.44 27.10

% C28 sterane 35.16 26.27 36.92 33.19

% C29 sterane 33.93 45.38 30.65 39.71

C29 20S/(20SC20R) 45.70 47.87 48.81 58.77

C29bb(20SC20R)/C29 bbCaa(20SC20R) 48.03 49.34 50.65 59.41

C29aa (20S)/C29 aa (20R) 0.84 0.92 0.95 1.43

20S/20R and bbb/abbCaaaZisomeric ratios from C29 steranes (%)

% Ro equ.Zvitrinite reflectivity equivalent[24]


8/12/2019 fuel 2005 (3)

6/10

4.3. FTIR and UV

4.3.1. Aliphatic and aromatic compounds determined

from FTIR

Fig. 11 shows two infrared spectra obtained from two

different oils. Globally the spectra seem to be very close but

some small variations can be seen particularly near

1500 cmK1.

Fig. 12shows that Rodaballo is the sample which has the

lowest aliphatic rate and the highest number of long chains,

when compared with the three other samples. The Boqueron

oil has a greater degree of aliphaticity and a lower long

chains rate. The two Casablanca oils have the greatest

degree of aliphaticity, particularly Casablanca 8. The lowest

long chains rate is detected in Casablanca 11. This diagram

does not show a clear differentiation between the Boqueron

and Casablanca 11 oils.

If we compare the aromaticity vs. FTIR substitution

2 indexes (Fig. 13), the results appear more accurate, with

the three groups of oils being better defined. The two

Casablanca oils form one group, and the Boqueron and

Rodaballo oils each form a group. These groups are

Fig. 6. GC/MS chromatogram corresponding to terpanes (191 ion).

Fig. 5. Gas chromatograms of studied topped oils (C15C).


8/12/2019 fuel 2005 (3)

7/10

Fig. 7. Tricyclic terpane diagram showing a discrete variation of source

rock deposition environment.

Fig. 8. C27, C28, C29 regular sterane distribution.

Fig. 9. Sterane GC/MS chromatograms, ion m/z217.

Fig. 10. Star diagrams. The Casablanca oils show a closed diagram between

them, and differ clearly from the Boqueron and Rodaballo oils.

Fig. 11. Infrared spectra of two different oils.


8/12/2019 fuel 2005 (3)

8/10

consistent with those determined by GC fingerprints

(Fig. 10).

4.3.2. Aromatic compounds determined from UV

The fluorescence indexes are related to a predominant

region for each type of condensation. In the studied oils,A3

was very small with the result that the number of

compounds with five or more aromatic rings was considered

to be insignificant. In this study, therefore, we present only

the results obtained in the A1 andA2 areas.

The fluorescence index (A2/A1 ratio,Fig. 4) proved to be

an accurate parameter to determine reservoir compartments

when combined with the FTIR substitution 1 index[9]. In

Fig. 14the three groups of crude oils, Boqueron, Casablanca

and Rodaballo can be distinguished very clearly. Casa-

blanca 8 and 11 oils form a very compact group related tothe single reservoir structure in accordance with the GC

fingerprints (Fig. 10).

4.4. Maturity degree

As shown inTable 1,a good correlation exists between

API gravity and top reservoir depths.

The results obtained by gas chromatographymass

spectrometry suggest that variations in hopanoids and

trisnorhopanes may be related to an increase in the maturity

degree from the Casablanca to the Rodaballo oils. Theincrease in maturity was also evidenced by sterane

isomerization [24] (Fig. 15A). A good correlation also

exists with API gravity (Fig. 15B).

The ratio between both aromaticity and aliphaticity

indexes shows an evolution path that can be related to the

degree of maturity [9]. In Fig. 16 samples are aligned

Fig. 12. Aromaticity vs. long chains index diagram.

Fig. 13. Aromaticity vs. substitution 2 index diagram. Three groups of

samples can be distinguished.

Fig. 14. Substitution 1 vs. fluorescence A2/A1 index diagram. A good

discrimination is shown between the three reservoir structures.

Fig. 15. (A) Regular sterane isomerization shows increasing maturity from

Casablanca to Rodaballo oils. (B) The increasing values of gravity

(API8degree) appear to be related to sterane isomerization.


8/12/2019 fuel 2005 (3)

9/10

8/12/2019 fuel 2005 (3)

10/10

References

[1] Larter SR, Aplin AC. Geological Soc Spec Publ 1995;86:522.

[2] England WA, Cubitt JM. Geological Soc Spec Publ 1995;86:13.

[3] Kaufman RL, Ahmed AS, Elsinger RL. GCS-SEPM Foundation

Ninth Annual Research Conference Proceeding, New Orleans

1990;26382.

[4] Hwang RJ, Ahmed AS, Moldowan JM. Org Geochem 1994;21:17188.

[5] Hwang RJ, Baskin DK. Middle East Pet Geosci Geo 1994;94(2):

52941.

[6] Magnier C, Trindade LAF. Rev Latin Am Geoqu Org 1999;5:2537.

[7] Magnier C, Trindade LAF, Becker M, Becker W, Cerqueira JR.

Proceedings of the International Meeting on Organic Geochemistry,

Istambul, Sept. 1999.

[8] Permanyer A, Douifi L, Lahcini A, Lamontagne J, Kister J. Fuel 2002;

81(7):8616.

[9] Permanyer A, Douifi L, Alberdi M, Rebufa C, Kister J. Eigth Latin-

American Congress on Organic Geochemistry 2002;1114.

[10] Albaiges J, Algaba J, Clavell E, Grimalt J. Org Geochem 1986;10:

44050.

[11] Garca-Sineriz B, Querol R, Castillo F, Fernandez JR. Proceedings of

the 10th World Petroleum Congress, Bucarest, vol. 4;1980 p. 14.

[12] Demaison G, Bourgeois FT. Am Assoc Pet Geologists Stud Geol

1985;18:15161.

[13] Seifert WK, Carlson RMK, Moldowan JM. Adv Org Geochem 1981

1983;71024.

[14] Seemann U, Pumpin VF, Casson N. AAPG Treatise Pet Geol, Atlas

Oil Gas Fields 1990;A-017:120.

[15] Berastegui X, Clavell E. Spec Publ Eur Assoc Pet Geoscientists 1991;

1:35568.

[16] Watson HJ. AAPG Memoir 1982;32:23750.

[17] Orlopp DE. Proceedings of the Offshore Technology Conference

1988.

[18] Doumenq P, Guiliano M, Mille G, Kister J. Anal Chim Acta 1991;

242:13741.

[19] Guiliano M, Mille G, Kister J, Muller JF. J Chim Phys 1988;85(10):

96370.

[20] Pieri N, Planche JP, Kister J. Analysis 1996;24:11322.

[21] Vo-Dinh T, Gammage RB, Martinez PR. Anal Chim Acta 1980;

118(2):31223.

[22] Kister J, Pieri N, Alvarez R, Diez MA, Pis JJ. Energy Fuels 1996;10:

94857.

[23] Peters KE, Moldowan JM. The biomarker guide, interpreting

molecular fossils in petroleum and ancient sediments. Englewood

Cliffs, NJ: Prentice Hall; 1993 p. 363.

[24] Bein A, Sofer Z. Am Assoc Pet Geol Bull 1987;71:6575.


fuel 2005 (3)

Documents

Transcript of fuel 2005 (3)