Study of the Composition of Gases Dissolved in Oil
Abstract Generated abstract
This study examines the determination of light gases dissolved in crude oils from several Tomsk Oblast fields using gas-liquid chromatography. The authors evaluate conditions based on an existing VNII petroleum-industry method, find inadequate separation of butane and pentane isomers under the prescribed setup, and propose modified chromatographic conditions using a KhL-4 instrument with ethyl bromide as a marker instead of ethyl chloride. Analyses of field samples show generally low dissolved gas contents, probably affected by volatilization during transport and storage, with better-preserved samples from the Sovetsko-Sosninsko-Medvedevskoye field showing higher gas yields and gas compositions dominated by n-butane and isobutane.
Full Text
STUDY OF THE COMPOSITION OF GASES DISSOLVED IN OIL
K. K. STRAMKOVSKAYA, S. I. SMOLYANINOV, L. A. PONOMAREVA,
A. F. KOTLOVA
(Presented by the scientific-methodological seminar of the Faculty of Chemical Technology)
As the basis for determining the gases dissolved in oils from fields of Tomsk Oblast, we adopted the gas–liquid chromatography method developed by the All-Union Scientific Research Institute of the Petroleum Industry (VNII—NP). According to this method, the composition of gases is determined directly from crude oil on a KhL-3 chromatograph; to the side fitting of this chromatograph, by means of a four-way valve, a preliminary distillation column with an electric furnace was connected, packed with Inza brick (fraction 0.25–0.5 mm). The amount of hydrocarbons was calculated with the aid of a “label,” for which VNII—NP recommends ethyl chloride. Preparation of the analyzed mixture of oil with the “label” substance was carried out in a special flask, into the tubus of which, in sealed ampoules, an accurately weighed amount of the “label” was placed. The flask was then weighed, the air was evacuated from it, and a definite amount of the oil sample to be analyzed was introduced. With a syringe needle the ampoule was broken, the oil and the “label” were mixed, and the resulting mixture was introduced into the preliminary distillation column, the temperature of which was maintained at 120°C. From the column the light hydrocarbons were swept into the chromatograph by the carrier gas.
It turned out that, under the conditions prescribed by the VNII—NP method, when the chromatograph column, 6 mm in diameter and 6 m long, is filled with tripoli from the Znkeevsky quarry (fraction 0.25–0.5 mm) with 8.5% vaseline oil, and the water-cooling column of this instrument is packed with CaX molecular sieves, with a carrier-gas flow rate of 40–50 ml/min, a column temperature of 40°C, and a detector current of 8.5 mA, the peaks were broad and diffuse, and the C₄ and C₅ isomers were poorly separated.
Good separation of the gases was obtained by us only when using a KhL-4 chromatograph, with a column diameter of 4 mm and length of 4.5 m, and with the column packed with TSEK containing 20% vaseline oil. However, in this case the peak of ethyl chloride, the “label,” emerged together with the isopentane peak.
When the indicated 20% phase was used, we selected ethyl bromide as the label; at a column temperature of 64°C, a helium flow rate of 100 ml/min, and a detector current of 100 mA, it emerged after the n-pentane peak. Its retention time relative to n-pentane was 1.667, and the mean weight sensitivity coefficient was \(K = 2.035\).
The use of ethyl bromide proved successful also because it simplified preparation of the analyzed mixture owing to the considerably
Places of oil sampling
Table 1
| No. | Code and oil sample | Field | Sampling date | Well No. | Perforation interval (sampling depth, m) | Formation No. | Place of sampling |
|---|---|---|---|---|---|---|---|
| 1 | TH-0 | Soviet-Sosninsko-Medvedevskoye | 28/XI 1963 | 18 | 2159–2164 | B-VIII | At the surface |
| 2 | TH-4 | Katylginskoye | 5/II 1965 | 91 | 2450–2462; 2468–2481 | — | At the wellhead |
| 3 | TH-8 | Latny-Yakskoye | March 1965 | 58 | 1534 | — | At the surface |
| 4 | TH-12 | Moiseevskoye | 28/III 1965 | 4 | 2606–2613; 2594–2604; 2587–2590 | — | At the surface |
| 5 | TH-18 | Soviet-Sosninsko-Medvedevskoye | July 1966 | 18 and 27 | — | — | Mixture from a gathering tank |
| 6 | TH-14 | — | 5/II 1966 | —18 | 2159–2164 | B-VIII | At the surface of the flow line |
| 7 | TH-21 | — | 26/IX 1966 | 18 | — | B-VIII | From a flowing well |
| 8 | TH-22 | — | 26/IX 1966 | 27 | 2144–2153 | B-VIII | From a flowing well |
| 9 | TH-23 | — | 26/IX 1966 | 47 | 1658–1688 | A-1 | From a flowing well |
| 10 | TH-15 | Sredne-Nyurolskoye | 26/IV 1966 | 41 | 2385–2395 | Yu-1 | From a flowing well |
of the higher boiling point of this substance compared with ethyl chloride, and it can be introduced into the oil without the precautions indicated above.
For the study, oil samples were taken from the Sovetsko-Sosninsko-Medvedevskoe, Lantyn-Yakh, Katylga, Moiseevskoe, and Sredne-Nyurolskoe fields; the sampling sites are given in Table 1.
Table 2
Content of gases dissolved in oil, wt. %, and their composition
| No. | Oil (sample code) | Gas yield up to \(C_4\) per oil, wt. % | Nitrogen | Methane | Ethane | Propane | Isobutane | n-Butane | Total |
|---|---|---|---|---|---|---|---|---|---|
| 1 | TN-0 | 0,35 | 1,0 | 0,0 | 0,0 | 1,6 | 20,0 | 77,4 | 100 |
| 2 | TN-4 | 1,08 | 0,1 | 0,1 | 0,9 | 18,1 | 19,3 | 61,3 | 100 |
| 3 | TN-8 | 0,03 | 58,8 | 0,0 | 0,0 | 0,0 | 0,0 | 41,2 | 100 |
| 4 | TN-12 | 0,27 | 2,5 | 0,2 | traces | 12,2 | 11,0 | 74,0 | 100 |
| 5 | TN-18 | 0,32 | 0,0 | 0,0 | 0,0 | 5,1 | 18,5 | 76,0 | 100 |
| 6 | TN-14 | 0,28 | 0,0 | 0,0 | 0,0 | 0,0 | 14,3 | 85,7 | 100 |
| 7 | TN-21 | 1,08 | 0,0 | 0,0 | 0,4 | 10,9 | 23,8 | 64,9 | 100 |
| 8 | TN-22 | 0,73 | 0,0 | 0,0 | 0,3 | 9,9 | 21,6 | 68,2 | 100 |
| 9 | TN-23 | 1,53 | 0,0 | traces | 0,5 | 15,7 | 19,4 | 64,4 | 100 |
| 10 | TN-15 | 1,10 | 0,0 | 0,0 | 0,0 | 12,4 | 18,5 | 69,1 | 100 |
Table 3
Content of gases dissolved in oil, wt. %, and their composition
| No. | Oil (sample code) | Gas yield up to \(C_5\) per oil, wt. % | Nitrogen | Methane | Ethane | Propane | Isobutane | n-Butane | Isopentane | n-Pentane | Total |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | TN-0 | 2,00 | 0,2 | — | — | 0,3 | 3,5 | 13,6 | 32,0 | 50,4 | 100 |
| 2 | TN-4 | 2,80 | 0,0 | 0,1 | 0,4 | 7,0 | 7,5 | 23,8 | 26,8 | 34,4 | 100 |
| 3 | TN-8 | 0,24 | 7,4 | — | — | — | — | 5,2 | 30,6 | 56,8 | 100 |
| 4 | TN-12 | 0,99 | 0,7 | — | — | 3,3 | 3,0 | 20,0 | 24,3 | 48,7 | 100 |
| 5 | TN-18 | 1,50 | — | — | — | 1,1 | 3,8 | 15,9 | 28,6 | 50,6 | 100 |
| 6 | TN-14 | 1,83 | — | — | — | — | 2,2 | 13,0 | 31,1 | 53,7 | 100 |
| 7 | TN-21 | 3,07 | — | — | 0,2 | 3,9 | 8,4 | 22,9 | 24,9 | 39,7 | 100 |
| 8 | TN-22 | 2,28 | — | — | 0,1 | 3,1 | 6,7 | 21,5 | 22,9 | 45,0 | 100 |
| 9 | TN-23 | 3,68 | — | traces | 0,2 | 6,5 | 8,1 | 26,8 | 23,3 | 35,1 | 100 |
| 10 | TN-15 | 2,61 | — | — | — | 5,1 | 7,7 | 28,6 | 28,2 | 30,4 | 100 |
The results of the analyses presented in Tables 2 and 3 showed that in these oil samples methane and ethane are almost absent; apparently, they volatilized during transport and storage of the samples, which accounts overall for the low content of dissolved gases in most samples.
In the oil of the Sovetsko-Sosninsko-Medvedevskoye field, samples of which were delivered in good packaging and stored for a short time, the total amount of dissolved gases is rather high and amounts, up to \(C_4\), to 1.08–1.53%, and up to \(C_5\), to 3.07–3.68%. The principal components of these gases, calculated up to \(C_4\), are n-butane, 64–68%, and isobutane, 19–23%.
Conclusions
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A method has been developed for determining gases in oil using ethyl bromide as a “marker” substance.
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The content and composition of gases dissolved in oil samples from the Sovetsko-Sosninsko-Medvedevskoye, Lantyn-Yakhskoye, and Sredne-Nyurolskoye fields have been determined.