Influence of Various Factors on the Pour Point of Crude Oils from Certain Fields in Western Siberia
Abstract Generated abstract
This study examines factors controlling the pour point of crude oils from several Western Siberian fields, treating pour point as an operational characteristic affected by prior handling and composition. The authors measured pour points under varying heat treatment temperatures, holding times, salt and water contents, surfactant additions, and mechanical stirring conditions. Heat treatment lowered the pour point of all investigated oils, with the strongest effects generally at 70 to 90°C and persistence for about 3 to 4 days, while prolonged holding at the treatment temperature and the presence of water or salts tended to raise the pour point. Surfactants and stirring reduced pour points, suggesting practical relevance for field oil treatment and pipeline transport design.
Full Text
INFLUENCE OF VARIOUS FACTORS ON THE POUR POINT OF CRUDE OILS FROM SOME FIELDS IN WESTERN SIBERIA
S. I. Smolyaninov, S. M. Katysheva, L. G. Gromova,
V. B. Levushkan, N. M. Smolyaninova
(Presented by the Scientific-Methodological Seminar of the Organic Departments)
The pour point of crude oil is not a physical constant, but only a technical characteristic by which the operational properties of the oil are judged [1].
It is known that the pour point depends to a significant extent on the preliminary heat treatment of the oil [2], on the content of paraffin and asphalt-resin substances [3, 4]. However, this question has not yet been studied sufficiently.
The present work is devoted to the study of the influence of various factors on the low-temperature properties of certain crude oils from Western Siberia. The oils from the Sovetskoye, Sobolinoye, Sredne-Norilskoye, Vartovskoye, Olenye, Samotlorskoye, and Luginetskoye fields were investigated; their physicochemical characteristics are given in Table 1.
The following factors affecting the pour point of crude oils were studied: heat-treatment temperature, holding time in the heated state and after heat treatment, as well as the content of salts, water, surfactants, and mechanical stirring.
The pour point was determined according to GOST 1533-42. Liquid nitrogen was used as the cooling agent, since it had been shown earlier that the pour point is practically independent of the cooling rate [5].
Table 2 gives the results of studying the effect of heat treatment on the pour point. It may be noted that the oils studied fully conform to the regularities established earlier [5], i.e., preliminary heating (heat treatment) leads to a lowering of their pour point. However, holding for a prolonged time in the heated state reduces the effect of heat treatment (Table 3).
For the oils investigated, a certain regularity is observed, according to which the heat-treatment temperature corresponding to the maximum lowering of the pour point lies within the range of 30–90°C. At temperatures of 70–90°C such a substantial effect is achieved that it indicates the possibility of its practical application.
However, without taking into account the influence of the holding time after heat treatment, it is impossible to decide on the prospects for using the heat-treatment effect in practice. Based on the data in Table 4, it may be noted that the heat-treatment effect is retained for 3–4 days; then the pour point of heat-treated oils begins to increase, reaching the pour point of the original oils.
Physicochemical characteristics of oils
Table 1
| Field | Specific gravity, $d_4^{20}$ | Molecular mass | Viscosity, cSt at 20°C | Viscosity, cSt at 50°C | Content, %: asphaltenes | Content, %: silica-gel resins | Content, %: sulfuric-acid resins | Content, %: paraffin yield | Content, %: paraffin pour point, °C | Yield of fractions, vol. %, up to 200°C | Yield of fractions, vol. %, up to 300°C |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Sovetskoye | 0,8442 | 193 | 6,33 | 3,54 | 0,55 | 8,99 | 11,4 | 3,27 | 47 | 33,5 | 56,5 |
| Sobolinoye | 0,8611 | 209 | 12,72 | 4,34 | 2,21 | 6,18 | 22,0 | 3,30 | 47 | 24,1 | 43,4 |
| Sredne-Nyurolskoye | 0,8257 | 184 | 6,21 | 3,32 | 0,25 | 7,14 | 20,0 | 6,88 | 47 | 39,4 | 60,2 |
| Luginetskoye | 0,8319 | 184 | 5,30 | 2,74 | 0,42 | 7,90 | 20,4 | 4,16 | 51 | 43,25 | 56,7 |
| Olenye | 0,8350 | 121 | 5,14 | 2,73 | 2,15 | 6,08 | 20,0 | 1,30 | 48 | 36,0 | 59,1 |
| Samotlorskoye | 0,8525 | 213 | 9,14 | 4,48 | 1,09 | 8,85 | 29,0 | 3,64 | 54 | 28,8 | 49,0 |
| Vartovskoye | 0,8128 | 154 | 6,10 | 2,87 | 0,80 | 3,93 | — | 17,68 | 49 | 56,9 | 69,9 |
| Typical oil | 0,8589 | 205 | 8,66 | 4,35 | 1,47 | 9,60 | 31,0 | 2,37 | 55 | 26,5 | 50,0 |
Table 2
Effect of heat-treatment temperature on the pour point of oil
| Heat-treatment temperature, °C | Sovetskaya | Olenya | Luginetskaya | Sredne-Nyurolskaya | Vartovskaya | Samotlorskaya | Sobolinaya |
|---|---|---|---|---|---|---|---|
| 20 | −7 | −17 | −22 | −1 | +11 | −11 | −6 |
| 40 | −12 | −29 | −9 | −20 | +4 | −2 | — |
| 50 | −15 | −30 | −14 | −29 | +7 | −4 | −23 |
| 60 | −25 | −31 | −22 | −34 | −1 | −9 | — |
| 70 | −36 | −35 | −33 | −36 | −4 | −24 | −27 |
| 80 | −29 | −34 | −30 | −28 | −2 | −27 | −14 |
| 90 | −26 | −30 | −24 | −24 | +10 | −23 | −12 |
| 100 | −16 | — | — | — | — | — | −10 |
Table 3
Effect of holding time in the heated state on pour point
| Oil name | Heat-treatment temperature, °C | 0 | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|---|---|
| Vartovskaya | 50 | +9 | +9 | +9 | +9 | +9 | +10 | +12 |
| Vartovskaya | 80 | −4 | +2 | +3 | +3 | +3 | +3 | +5 |
| Sredne-Nyurolskaya | 50 | −29 | −29 | −29 | −28 | −24 | −20 | −18 |
| Sredne-Nyurolskaya | 70 | −36 | −39 | −39 | −39 | −38 | −33 | −28 |
| Sovetskaya | 50 | −15 | −15 | −15 | −15 | −12 | −8 | −5 |
| Sovetskaya | 70 | −36 | −48 | −48 | −48 | −47 | −45 | −42 |
| Olenya | 50 | −30 | −30 | −30 | −30 | −30 | −28 | −23 |
| Olenya | 70 | −35 | −40 | −40 | −40 | −40 | −39 | −36 |
| Samotlorskaya | 50 | −4 | −4 | −4 | −4 | −3 | +1 | +2 |
| Samotlorskaya | 80 | −27 | −35 | −35 | −35 | −35 | −33 | −31 |
| Luginetskaya | 50 | −14 | −14 | −14 | −14 | −14 | −13 | −10 |
| Luginetskaya | 70 | −33 | −36 | −36 | −36 | −36 | −35 | −33 |
| Sobolinaya | 50 | −23 | — | −10 | — | −10 | — | — |
| Sobolinaya | 70 | −22 | — | −14 | — | −14 | — | — |
Table 4
Effect of holding time after heat treatment on the pour point of oil
| Oil name | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| Sovetskaya | −34 | −26 | −21 | −16 | −9 | −6 |
| Sobolinaya | −27 | −12 | −10 | −8 | −8 | −6 |
| Sredne-Nyurolskaya | −22 | −16 | −11 | −8 | −5 | −4 |
Pour point, °C, during holding of the oil (days) after heat treatment at 70°C
Thus, the effect of heat treatment is preserved for a fairly long period of time, which, apparently, can be used when transporting oil through pipelines.
The effect of salt and water content on the pour point is shown in Table 5. Unfortunately, the question of the influence of water and salts on the pour point of oils has not been studied, but it may be assumed that water and salts affect the mechanism of paraffin crystallization.
From the data in Table 6 it can be seen that the addition of alkyl sulfates leads to a decrease in pour point.
Table 5
Effect of salt and water content on the pour point of oils
| Oil name | Pour point, °C: salt content in dehydrated oil, % — 0.0 | 0.01 | 0.25 | 0.5 | 1 | Pour point, °C: water content, % of dehydrated oil — 0 | 0.5 | 1 | 2 |
|---|---|---|---|---|---|---|---|---|---|
| Samotlor | −11 | −10 | −7 | −6 | −2 | −11 | −8 | −6 | −2 |
| Vartovskaya | +11 | +13 | +15 | +16 | +17 | +10 | +11 | +12 | +14 |
| Sovetskaya | −7 | −2 | 0 | −1 | +2 | −7 | −5 | −4 | −2 |
| Olenya | −17 | −16 | −13 | −10 | −17 | −17 | −13 | −12 | −11 |
| Sredne-Nyurolskaya | −1 | +1 | +4 | +5 | +6 | −1 | 0 | +2 | +3 |
| Luginetskaya | −22 | −21 | −14 | −13 | −10 | −22 | −15 | −13 | −10 |
Table 6
Effect of surfactants on the pour point of oils
| Oil name | Treatment temperature, °C | Pour point, °C: content of alkyl sulfates from alcohols C₁₀–C₁₈ — 0.0 | 0.01 | 0.2 | 0.5 | Pour point, °C: content of alkyl sulfates from sperm oils — 0.01 | 0.2 | 0.5 |
|---|---|---|---|---|---|---|---|---|
| Luginetskaya | 20 | −22 | −20 | −17 | −14 | −16 | −10 | −9 |
| Luginetskaya | 50 | −14 | −16 | −19 | −20 | −19 | −23 | −26 |
| Luginetskaya | 70 | −33 | −37 | −40 | −41 | −35 | −38 | −39 |
| Sovetskaya | 20 | −7 | −5 | −1 | 0 | −5 | −4 | −2 |
| Sovetskaya | 50 | −15 | −16 | −18 | −19 | −17 | −21 | −24 |
| Sovetskaya | 70 | −36 | −38 | −41 | −42 | −37 | −39 | −41 |
The study also showed that, when oils are stirred, they solidify at a lower temperature than at rest. This phenomenon is apparently associated with the destruction of coagulation structures of paraffin, leading to a decrease in the pour point.
Conclusions
-
Oils from the Sovetskoye, Sobolinoye, Sredne-Nyurolskoye, Vartovskoye, Olenye, Samotlor, and Luginetskoye fields were studied. It was established that heat treatment leads to a decrease in their pour point; the maximum effect of heat treatment is achieved at 70–90°C and is retained for up to 3–4 days.
-
Surfactants and mechanical stirring lower the pour point, while prolonged holding of the oil at the heat-treatment temperature and the presence of water and salts increase it.
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The data obtained may be taken into account in designing installations for oil treatment at oil fields.
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