Rheological Studies of Oils from Fields in Western Siberia
Abstract Generated abstract
This study examines the rheological behavior of paraffinic oils from several Western Siberian fields, focusing on viscosity, pour point, and yield shear stress as affected by composition and thermal treatment. Using rotational viscometry and comparative measurements before and after heating, the authors relate anomalous viscosity and high pour points to paraffin crystallization and the formation of a structural lattice, modified by asphalt-resin components. The experiments indicate that heating in the range of about 60 to 70°C substantially lowers viscosity, pour point, and limiting shear stress for most samples, while lower preliminary heating may increase effective viscosity. The beneficial effect of heat treatment persists for approximately 2 to 3 days, after which recrystallization of paraffin hydrocarbons appears to restore the original flow properties.
Full Text
RHEOLOGICAL STUDIES OF OILS FROM FIELDS OF WESTERN SIBERIA
S. I. Smolyaninov, V. B. Levushkan, N. V. Nikolaeva
(Presented by the scientific-methodological seminar of the organic departments of the Faculty of Chemical Technology)
The production and pumping of paraffinic oils are associated with a number of difficulties and still remain an unresolved problem. The reason for this lies in the insufficient study of the rheological properties of such oils [1].
We have carried out a study of the viscosity–temperature dependence of oils and of the influence on it of heat treatment of the oil and of holding time at the optimum temperature. The oils studied were those whose physicochemical properties are given in Table 1.
In the course of the work, the following parameters of the original and heat-treated oil were measured: viscosity, pour point, and yield shear stress. The structural-mechanical properties were studied on an RV-8 rotational viscometer. The experimental results characterizing the change in the rheological properties of oils as a function of heat-treatment temperature are given in Table 2.
The rheological parameters of oils are determined by the ratio of the components entering into their composition [2]. Viscosity and pour point depend strongly on the content of paraffin in the oils. As long as the paraffin is dissolved in the oil, it has little effect on the viscosity, which at that time is determined by the viscosity of the fractions composing the oil. When the oil is cooled to a certain temperature, paraffin crystals form a three-dimensional structural lattice, in the cells of which the liquid phase of the oil is immobilized [3]. Thus, structure formation in high-pour-point oils is the cause of viscosity anomaly, thixotropy, and a high pour point.
It should also be noted that the asphalt-resin substances contained in the oil participate in the formation of the paraffin structural lattice. The latter are adsorbed on the surface of paraffin crystals and hinder the separation of the solid phase upon cooling of paraffinic resinous products, which causes a decrease in the pour point and viscosity [4]. The smaller the ratio of paraffin to the content of asphalt-resin substances, the greater the effect of heat treatment. This is clearly observed for the South-Cheremshansk oil, which is characterized by a low ratio of paraffin to asphalt-resin substances.
In addition, from the data of Table 2 it is seen that preliminary heating of paraffinic oils (to 30–45°C) increases the effective viscosity; a subsequent increase in heating to 60°C and higher leads—
Physico-chemical properties of oils
Table 1
| Oil | Well No. | Specific gravity, \(d_4^{20}\) | Molecular mass | Kinematic viscosity, cSt at \(20^\circ\text{C}\) | Kinematic viscosity, cSt at \(50^\circ\text{C}\) | Pour point, \(^{\circ}\text{C}\), without heat treatment | Pour point, \(^{\circ}\text{C}\), with heat treatment at \(500^\circ\text{C}\) | Content, %: asphaltenes | Content, %: silica-gel resins | Content, %: sulfur-containing | Content, %: paraffin | Paraffin cloud point, \(^{\circ}\text{C}\) | Fractional composition: up to \(200^\circ\) | Fractional composition: up to \(300^\circ\) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| South-Cheremshan | 335 | 0.8395 | 176 | 5.06 | 2.68 | −26 | −32 | 3.59 | 7.15 | 40 | 2.057 | 50.0 | 38.0 | 58.0 |
| Krapivinskaya | 196 | 0.8522 | 194 | 6.67 | 3.41 | −27 | −39 | 1.79 | 8.14 | 28 | 1.39 | 52.3 | 34.0 | 56.2 |
| Strezhevskaya | P-14 | 0.8556 | 200 | 10.91 | 4.92 | −4 | −11 | 1.08 | 10.25 | 20 | 4.37 | 51.5 | 24.5 | 49.2 |
| Luginetskaya | 166 | 0.8285 | 182 | 4.70 | 2.53 | −8 | −41 | 0.05 | — | 12 | 3.70 | 52.5 | 30.5 | 61.0 |
| Kiev-Eganskaya | P-150 | 0.8080 | 165.8 | 2.51 | 1.68 | −16 | −41 | 0.24 | 0.24 | 6.1 | 5.27 | 48.5 | 44.0 | 71.0 |
| Typical | — | 0.8539 | 205 | 8.06 | 4.35 | −14 | −7 | 1.47 | 9.61 | 31 | 3.37 | 55.5 | 26.5 | 50.0 |
Table 2
Dependence of the rheological properties of oils on the thermotreatment temperature
| Oil | Thermotreatment temperature, °C | Wax content, % | Viscosity, P at −40°C | Viscosity, P at −18°C | Viscosity, P at −8°C | Viscosity, P at +20°C | Viscosity, P at +30°C | Viscosity, P at +50°C | Pour point temperature, °C | Temperature of hardening upon cooling in a rheometer after thermotreatment: 1 | Temperature of hardening upon cooling in a rheometer after thermotreatment: 2 | Temperature of hardening upon cooling in a rheometer after thermotreatment: 3 | Temperature of hardening upon cooling in a rheometer after thermotreatment: 4 | Temperature of hardening upon cooling in a rheometer after thermotreatment: 5 | Temperature of hardening upon cooling in a rheometer after thermotreatment: 6 | Limiting shear stress, dyn/cm² at −40°C | Limiting shear stress, dyn/cm² at −30°C |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Luginetskaya | initial | 4,49 | 1,60 | 1,20 | — | — | 0,521 | 0,42 | −8 | — | — | — | — | — | — | 558 | — |
| Luginetskaya | 50 | 3,11 | 1,040 | 0,646 | 0,350 | 0,303 | 0,208 | — | −44 | — | — | — | — | — | — | 262 | 131 |
| Luginetskaya | 70 | 1,55 | 0,755 | — | 0,303 | 0,253 | — | 0,188 | −53 | −53 | −53 | −51 | −50 | −38 | −10 | 72,6 | 0 |
| Typical | initial | 7,34 | — | — | 0,903 | 0,455 | 0,446 | 0,405 | −14 | — | — | — | — | — | — | 310 | 65,6 |
| Typical | 50 | 8,04 | 1,640 | 0,968 | 0,587 | — | 0,521 | 0,476 | −7 | — | — | — | — | — | — | 361 | 147,6 |
| Typical | 70 | 5,08 | 0,948 | — | — | — | 0,425 | 0,347 | −43 | −43 | −43 | −43 | −40 | −34 | −28 | 233 | 24,6 |
| Yuzhno-Cheremshanskaya | initial | 5,48 | — | — | 1,30 | 0,586 | — | 0,404 | −26 | — | — | — | — | — | — | 636 | 191 |
| Yuzhno-Cheremshanskaya | 50 | 4,80 | 1,540 | — | — | 0,586 | 0,418 | 0,392 | −32 | — | — | — | — | — | — | 559 | 57,4 |
| Yuzhno-Cheremshanskaya | 70 | 3,32 | 0,935 | — | — | — | — | 0,314 | −57 | −57 | −57 | — | −52 | −42 | −23 | 210 | 8,2 |
| Krapivinskaya | initial | 10,8 | 2,54 | 1,60 | 1,025 | 0,850 | — | — | −27 | — | — | — | — | — | — | 459 | — |
| Krapivinskaya | 50 | 3,36 | — | — | 0,467 | — | — | — | −39 | — | — | — | — | — | — | 230 | — |
| Krapivinskaya | 70 | 2,08 | — | 0,607 | 0,269 | — | — | — | −50 | −50 | −50 | −50 | −44 | −37 | −27 | 98,5 | — |
| Strezhevaya | initial | — | 1,90 | 1,36 | 0,733 | — | — | 0,44 | −4 | — | — | — | — | — | — | — | 328 |
| Strezhevaya | 50 | — | — | — | — | — | — | — | −11 | — | — | — | — | — | — | — | — |
| Strezhevaya | 60 | — | — | — | — | — | — | — | −14 | −14 | −14 | −14 | −4 | −4 | −4 | — | — |
| Strezhevaya | 70 | — | — | — | — | — | — | — | −9 | — | — | — | — | — | — | — | — |
| Kiev-Egan | initial | — | 0,965 | — | 0,285 | — | — | 0,219 | −16 | — | — | — | — | — | — | — | 219 |
| Kiev-Egan | 50 | — | — | — | — | — | — | — | −37 | — | — | — | — | — | — | — | — |
| Kiev-Egan | 70 | — | — | — | — | — | — | — | −47 | −47 | −47 | −40 | −33 | −25 | −16 | — | — |
led to a sharp decrease in the pour point and viscosity. Probably, during heat treatment a molecular rearrangement occurs, an ordering of the crystal lattice of the paraffin [5].
The results of the experiments showed (Table 2) that the heat-treatment temperature in the range of 60–70°C is optimal. In this case the effect of heat treatment is retained for 2–3 days, and then the pour point begins to rise, reaching the pour point of the untreated oil. The disappearance of the heat-treatment effect can be explained by recrystallization of the paraffin hydrocarbons, leading to a change in the geometry of the crystals, which in turn affects the formation of the coagulation structure of these crystals.
Conclusions
-
A significant change in the rheological properties of most oils as a result of heat treatment has been established.
-
It has been shown that the presence of paraffin crystals in a certain temperature interval does not affect the rheological properties of the oil.
-
The optimal heat-treatment temperature is 60–70°C; the effect of heat treatment is retained for 2–3 days.
References
-
Shikhlinskaya D. E., Abdurashitov S. A. Izv. vuzov, “Neft’ i gaz,” 1968, No. 3, pp. 61–64.
-
Urazgaliev V. Ts., Belik P. A., Kosgebener Zh. E. Proceedings of the Institute of Petroleum Chemistry and Natural Salts. Alma-Ata, Publishing House of the Academy of Sciences of the Kazakh SSR, 1970, pp. 3–9.
-
Rebinder P. A. Physicochemical Mechanics of Disperse Structures. Moscow, “Nauka,” 1966.
-
Pipeline Transport of Highly Viscous and High-Pour-Point Oils. Thematic scientific and technical reviews of VNIIOENG. Moscow, 1968.
-
Chernikin V. I. Pumping of Viscous and Pour-Point Oils. Moscow, Gostoptekhizdat, 1958.
-
Koten V. G., Stoyanovskaya L. I. Problems of rheology and exploitation of oil fields of Turkmenia. Moscow, State Scientific and Technical Publishing House of Petroleum and Mining-Fuel Literature, issue 5, 1962, pp. 226–229.