354

ISSN 0965-5441, Petroleum Chemistry, 2009, Vol. 49, No. 5, pp. 354–359. ©

Pleiades Publishing, Ltd.

, 2009.Original Russian Text © S.S. Yanovskaya, T.A. Sagachenko, 2009, published in Neftekhimiya, 2009, Vol. 49, No. 5, pp. 374–379.

Data on the compositions of crude oils and theorganic matter (OM) of oil-prone source rocks are ofgreat importance for obtaining reliable informationabout the prospects of oil-and-gas reserves of individ-ual lithological–stratigraphic strata, the assessment ofhydrocarbon stock resources, and the prediction of itsquality. A wealth of material has been accumulated todate to characterize the hydrocarbon composition ofvarious OM types, coals, oils, and condensates [1–3].The data on heteroatomic compounds, in particular,nitrogen-containing compounds, mainly concern oils.It has been found that basic, weakly basic, and neutralnitrogen components are present in different oils,largely, as pyridine, pyridone, and carbazole derivatives[4, 5]. Investigations concerning the distribution andcomposition of these components in sedimentary rockshave been made predominantly by foreign scholars [5–12]. Note that the main publications deal with the dis-tribution and composition of neutral nitrogen com-pounds. The information on the principal compounds islimited, and there are barely any data on weakly basiccompounds.

The attention given to low-molecular-mass nitrogencompounds is mainly due to the fact that they have anunfavorable effect on the catalytic processing of hydro-carbon feedstock and the technical characteristics offuels and lubricants [4]. On the other hand, being chem-ically and thermally stable, low-molecular-mass nitro-gen compounds can be used, along with other petro-leum components, for studying the deposition forma-tion processes [5–7].

In this paper, we present data on the characteristicfeatures of the distribution of low-molecular-massnitrogen bases in crude oils and dispersed organic mat-

ter (DOM) in Upper Jurassic deposits of Western Sibe-ria, which form the main oil-and-gas play of the region.

EXPERIMENTAL

The DOM of Bazhenov rocks and oils from Vasyu-gan reservoirs of the corresponding areas were investi-gated. Rocks and oils were sampled at the depth rangesof 2414.6–2833.5 and 2452–2849 m, respectively, fromthe areas in the southeast part of Western Siberia withinTomsk oblast.

Bitumenoid was isolated by the standard procedure[13] according to which rock is mechanically ground toa particle size of 0.2–0.5 mm, placed into filter papercartridges, and extracted with a 7 vol % methanol solu-tion in chloroform using a Tecotor Soxtec HT systemover 2 h. Then, the cartridges were placed into a flaskand extracted with a fresh portion of the solvent for anhour. The extracts were combined, an the solvent wasevaporated under a vacuum to a constant weight.

Low-molecular-mass nitrogen compounds wereextracted from bitumenoids and oils with an aqueousblend composed of sulfuric acid, acetic acid, and waterin a 25 : 60 : 15 ratio [14]. This extractant makes it pos-sible to extract from complex organic mixtures nitrogencompounds that have an average molecular mass of250–350 Da and are represented by strong and weakbase components.

The concentrates obtained were subjected to chro-matographic separation on silicic acid using a sample toadsorbent ratio of 1 : 100. Toluene, toluene–diethylether (1 : 1 v/v), and toluene–ethanol (5 : 1 v/v) weresuccessively used for elution to give fractions F

1

, F

2

,and F

3

, respectively. The separation process was moni-

Distribution of Low-Molecular-Mass Nitrogen Compounds in Crude Oils and Organic Matter of Upper Jurassic Rocks

of Western Siberia

S. S. Yanovskaya and T. A. Sagachenko

Institute of Petroleum Chemistry, Siberian Branch, Russian Academy of Sciences, Tomsk, Russiae-maill: azot@ipc.tsc.ru

Received January 2, 2009

Abstract

—The distribution of low-molecular-mass nitrogen-containing components of oils and dispersedorganic matter in the Upper Jurassic play of Western Siberia has been studied. It has been found that theiramount in the organic matter of rocks is higher than that of corresponding oils. In all test samples, low-molec-ular-mass nitrogen compounds are represented by a mixture of strong and weak bases. The qualitative compo-sition of these compounds is the same. The nitrogen bases of the dispersed organic matter differ from petroleumbases by an increased amount of weakly basic components and structures with unhindered nitrogen atoms.

DOI:

10.1134/S0965544109050028

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DISTRIBUTION OF LOW-MOLECULAR-MASS NITROGEN COMPOUNDS 355

tored by following the absorbance measured on aSpecord-21 spectrophotometer at

λ

= 325 nm. The des-orption was exhaustive in all cases.

The total nitrogen content (N

t

) was determined bythe combustion method in a Pokrovskii reactor [15], thebasic (N

b

) and weakly basic (N

wb

) nitrogen contentswere determined by nonaqueous potentiometric titra-tion with a chloric acid solution in dioxane in an aceticanhydride medium [16]. The IR spectra were recordedon a Specord M-80 spectrophotometer in the range of4000–500 cm

–1

as a film from a chloroform solution.

RESULTS AND DISCUSSION

As follows from the data presented in Table 1, thetotal nitrogen content (N

t

) of test oils varies within quitea broad range, being on average 0.10 wt %. The basenitrogen content (N

b

) varies from 0.004 to 0.029 wt %(on average 0.022 wt %). The N

t

concentration in therock OM is significantly higher than that in oils (onaverage 0.89 wt %), whereas the N

b

fraction is smaller(on average 14.2 against 21.6 rel %). Another specificfeature of nitrogen compounds in rock OM is a higher

content of low-molecular-mass components. On aver-age, 2.71 wt % of low-molecular-mass components isextracted from DOM and only 0.15 wt % from oils(Table 2). The fact of a higher content of low-molecu-lar-mass nitrogen compounds in DOM in comparisonwith oils was also noted in [5, 6, 8].

The elemental and functional analysis data showthat all the concentrates are mixtures of strong andweak nitrogen bases (N

t

= N

b

+ N

wb

). The degree ofrecovery of low-molecular-mass strong bases fromDOM is 21.2–31.9 (on average 26.0 rel %). For oils,this value is lower (12.7–16.6 or 14.5 rel % on average).The degree of extraction of weak bases into the concen-trate was not evaluated because of possible errors in thedetermination of the absolute content of weak-basenitrogen of the initial samples by nonaqueous potentio-metric titration [17].

The concentrates extracted from oils and DOM dif-fer in the ratio of strong to weak nitrogen bases. Thestrong bases predominate among petroleum nitrogencompounds (60.4–79.9, or 70.3 rel % on average). Therelative amounts of strong and weak bases in DOMnitrogen compounds are practically the same (37.3–

Table 1.

Characteristics of oils and DOM of Upper Jurassic rocks of Western Siberia

Sample no.* Area, well number Occurrence depth, m

Content, wt %N

b

/N

t

×

100, %N

t

N

b

Crude oils

1 Boltnaya, 1 2452–2460 0.02 0.004 20.0

2 Fedyushkinskaya, 2 2844–2849 0.13 0.028 21.5

3 Yasnaya, 21 2641–2653 0.13 0.029 22.3

4 Kvartovaya, R-3 2595–2602 0.10 0.021 21.0

5 Pervomaiskaya, 270 2536–2539 0.11 0.025 22.7

6 Krapivinskaya, 191 2644–2648 0.08 0.019 23.7

7 Stolbovaya, 75 2595–2598 0.13 0.026 20.0

DOM

8 Boltnaya, 1 2414.6 1.20 0.188 15.7

9 Boltnaya, 1 2419.6 0.76 0.130 17.1

10 Fedyushkinskaya, 4 2833.5 0.63 0.100 15.9

11 Yasnaya, 20 2642.1 1.16 0.130 11.2

12 Kvartovaya, 10 2613.7 0.95 0.130 13.7

13 Pervomaiskaya, 2278 2548.0 0.76 0.126 16.6

14 Krapivinskaya, 211 2695.1 0.94 0.120 12.8

15 Krapivinskaya, 191 2637.4 0.99 0.124 12.5

16 Stolbovaya, 89 2601.1 0.62 0.079 12.7

* Sample numbering is the same throughout all Tables.

356

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YANOVSKAYA, SAGACHENKO

47.9 and 52.1–62.7 or, on average, 45.0 and 55.0 rel %,respectively).

The IR data show a resemblance in the qualitativecomposition of low-molecular-mass nitrogen com-pounds between oils and DOM. The vibration spectraof the concentrates display absorption bands of strongpyridine bases (inflections in the range of 1580–1520 cm

–1

); cyclic amides, which are categorized withweak bases (3450–3300 and 1660 cm

–1

); and carboxy-lic compounds (3200, 1715 cm

–1

) [18]. The last com-pounds, depending on the position of the carboxylgroup, can possess both strong base (the remote posi-tion of the carboxyl group from the nitrogen atom) andweak base (the nearest position to the nitrogen atom)properties [19].

The resemblance in the qualitative composition oflow-molecular-mass nitrogen compounds between oilsand DOM is also shown by their fractionation on silicicacid (Tables 3 and 4). In both cases, the components ofinterest are distributed in three fractions. Oils are char-acterized by a higher content (on average 59.7 rel %),

relative to DOM (30.0 rel % on average), of chromato-graphically mobile compounds eluted as fraction F

1

.The content of strongly sorbed components of rock OMeluted as fractions F

2

and F

3

is higher than that of oils(on average 40.1 against 30.6 and 29.9 against 9.7 rel %,respectively).

According to the functional analysis data, the chro-matographically mobile compounds of the F

1

fractionsof oil and DOM samples are represented by only strongbases, whereas the less chromatographically mobilecompounds of fractions F

2

and F

3

are represented by amixture of strongly and weakly basic components(Tables 3 and 4). According to published data [20], thechromatographic mobility of nitrogen compoundsdepends on the degree of shielding of the nitrogen atomin the molecule. The character of distribution of low-molecular-mass nitrogen bases over the separationproducts indicates that the hindered structures prevailamong strong and weak bases of oils, whereas slightlyhindered structures dominate the low-molecular-massbases of rock OM. For example, the major portion of

Table 2.

Characteristics of concentrates of low-molecular-mass nitrogen compounds isolated from oils and rock DOM

Sample no.

Yield,wt %

Content, %

N

b

/N

t

×

100, % N

wb

/N

t

×

100, %N

t

N

b

N

wb

abs. abs. rel.* abs.

Oils

1 0.04 2.45 1.48 14.8 0.97 60.4 39.6

2 0.14 3.18 2.54 12.7 0.64 79.9 20.1

3 0.20 3.24 2.40 16.6 0.84 74.1 25.9

4 0.14 2.98 2.18 14.5 0.80 73.2 26.8

5 0.18 2.78 2.03 14.6 0.75 73.0 27.0

6 0.14 3.08 2.08 15.3 1.00 67.5 32.5

7 0.20 2.65 1.70 13.1 0.95 64.2 35.8

DOM

8 5.45 2.30 0.95 27.5 1.35 41.3 58.7

9 2.90 3.03 1.43 31.9 1.60 47.2 52.8

10 2.00 2.69 1.28 25.6 1.41 47.6 52.4

11 2.00 2.88 1.38 21.2 1.50 47.9 52.1

12 3.47 2.60 0.97 25.9 1.63 37.3 62.7

13 2.53 2.59 1.21 24.3 1.38 46.7 53.3

14 2.20 2.87 1.27 23.3 1.60 44.3 55.7

15 2.00 3.54 1.64 26.4 1.90 46.3 53.7

16 1.80 2.65 1.23 28.0 1.42 46.4 53.6

* Calculation was made by the formula: N

b

, rel % = (Concentrate yield, wt %

×

N

b

, abs. % in concentrate)/N

b

, abs. % in oil or DOM.

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DISTRIBUTION OF LOW-MOLECULAR-MASS NITROGEN COMPOUNDS 357

strong bases of oils (on average 80.3 rel %) passes intofractions F

1

, whereas the majority of strong bases ofDOM are distributed into fractions F

2

(on average26.9 rel %) and F

3

(on average 35.1 rel %). Most ofweakly basic nitrogen compounds of both oils andDOM are represented by hindered structures, which areconcentrated in fractions F

2

. However, their proportionin DOM is lower than in oils (on average 76.4 versus84.8 rel %). At the same time, the relative amount ofweak bases with the unhindered nitrogen atom elutedwith fraction F

3

is higher than that in oils (on average23.6 versus 15.2 rel %). The prevalence of the unhin-dered structures among strong and weak bases of therock OM can be due to weak adsorption of the hinderedisomers on clay minerals and/or to their low solubilityin brine water [6].

A comparative analysis of the data on the distribu-tion of low-molecular-mass nitrogen components in

oils and DOM of Upper Jurassic rocks of Western Sibe-ria leads to the following conclusions.

The amount of low-molecular-mass nitrogen com-pounds of the organic matter of rocks is considerablyhigher than that of crude oils from the correspondingareas. These compounds in oils and DOM are repre-sented by a mixture of strong and weak bases. The qual-itative composition of these compounds is the same.The specifics of DOM nitrogen bases is an increasedcontent of slightly hindered structures. The revealeddifferences in the distribution and composition of low-molecular-mass nitrogen bases between oils and DOMcan be associated with the fractionation of these com-ponents during the primary migration of oil [5, 6, 8,21]. The results of this study are important for resolvingthe problems related to the generation and transforma-tion of oils in the sedimentary environment, the predic-tion of the quality of hydrocarbon resources, and the

Table 3.

Fractionation of low-molecular-mass nitrogen compounds isolated from oils

Sample no. Fraction Mass of

fraction, gYield of fraction,

rel %

Content, %

N

b

N

wb

abs. rel. abs. rel.

1 F

1

0.0951 60.8 1.93 79.3 none –

F

2

0.0489 31.3 0.68 14.4 2.72 87.8

F

3

0.0124 7.9 1.18 6.3 1.50 12.2

2 F

1

0.0837 62.4 3.24 79.6 none –

F

2

0.0381 28.4 1.26 14.1 1.83 81.2

F

3

0.0123 9.2 1.74 6.3 1.32 18.8

3 F

1

0.0666 63.9 3.03 80.7 none –

F

2

0.0277 26.6 1.14 12.5 2.62 83.0

F

3

0.0099 9.5 1.69 6.7 1.50 17.0

4 F

1

0.0736 61.5 2.90 81.8 none –

F

2

0.0332 27.7 0.95 12.1 2.55 88.3

F

3

0.0129 10.8 1.24 6.1 0.85 11.7

5 F

1

0.0514 54.1 2.98 79.4 none –

F

2

0.0316 33.3 0.89 14.6 1.94 86.1

F

3

0.0120 12.6 0.97 6.0 0.83 13.9

6 F

1

0.0698 57.2 2.96 81.4 none –

F

2

0.0397 32.5 0.79 12.3 2.53 82.2

F

3

0.0126 10.3 1.27 6.3 1.73 17.8

7 F

1

0.0724 58.2 2.33 79.8 none –

F

2

0.0425 34.2 0.68 13.7 2.36 85.0

F

3

0.0094 7.6 1.45 6.5 1.87 15.0

358

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YANOVSKAYA, SAGACHENKO

selection of methods for their producing and pro-cessing.

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Petroleum Hydrocarbons

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Table 4.

Fractionation of low-molecular-mass nitrogen compounds isolated from DOM

Sample no. Fraction Mass of

fraction, gYield of fraction,

rel %

Content, %

N

b

N

wb

abs. rel. abs. rel.

8 F

1

0.0360 34.0 1.06 38.0 none –

F

2

0.0402 38.0 0.65 26.0 2.66 74.9

F

3

0.0297 28.0 1.22 36.0 1.21 25.1

9 F

1

0.0203 27.8 1.81 35.2 none –

F

2

0.0277 38.0 1.19 31.6 3.28 78.0

F

3

0.0249 34.2 1.39 33.2 1.03 22.0

10 F

1

0.0308 30.4 1.47 35.0 none –

F

2 0.0389 38.4 1.03 30.9 2.79 75.9

F3 0.0316 31.2 1.40 34.1 1.09 24.1

11 F1 0.0224 30.8 1.82 40.6 none none

F2 0.0269 36.9 0.89 23.8 3.14 77.2

F3 0.0235 32.3 1.52 35.6 1.06 22.8

12 F1 0.0191 18.2 2.24 41.9 none –

F2 0.0550 52.4 0.48 25.9 2.52 81.0

F3 0.0308 29.4 1.06 32.1 1.05 19.0

13 F1 0.0151 29.3 1.43 34.6 none –

F2 0.0224 43.4 0.71 25.5 2.32 73.0

F3 0.0141 27.3 1.77 39.9 1.36 27.0

14 F1 0.0316 34.2 1.38 37.2 none –

F2 0.0357 38.6 0.87 26.4 2.96 71.4

F3 0.0252 27.2 1.70 36.4 1.68 28.6

15 F1 0.0198 29.3 2.07 37.0 none –

F2 0.0264 39.1 1.23 29.3 3.81 78.4

F3 0.0214 31.6 1.75 33.7 1.30 21.6

16 F1 0.0305 36.0 1.43 41.9 none –

F2 0.0309 36.5 0.77 22.8 3.04 78.1

F3 0.0233 27.5 1.58 35.3 1.18 22.9

PETROLEUM CHEMISTRY Vol. 49 No. 5 2009

DISTRIBUTION OF LOW-MOLECULAR-MASS NITROGEN COMPOUNDS 359

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