Of late, high-viscosity oil fields are being developed to broaden the feedstock base of the oil refining industry. High viscosity of such oils renders their extraction and transportation difficult. To improve the rheological properties of high-viscosity crude oils, use is made of chemical reagents [1], surfactants [2, 3], dispersing additives [4], and magnetic field [5, 6].

The rheological properties of the oils were investigated on a Rheotest-2 rotary viscometer in the 20-60°C range at shear rates from 3 to 1312 sec-1. Oils from Rodino wells 1200 (specimen I) and 306 (specimen II) and Baklanovo fields (specimen III) were investigated. The physicochemical properties of the oils are adduced in Table 1. As evident from this table, the oils are distinguished by high content of aromatic hydrocarbons, resins, and asphaltenes.

Table 1  
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In order to improve the rheological properties of the oils, we used the reagents Neonol AF 9-12, Reapon IF, SNPKh 4880 D2, ETN-7r-14, IPG-12, Laprol, Sonpar, and copolymer of ethylene with vinyl acetate (vinyl acetate 26-30%). The IR spectra of the reagents were obtained on a Shimadzu spectrophotometer. The main functional groups of the reagents are characterized in Table 2.

Table 2  
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The stretching vibration bands of hydrogen bonds of hydroxyl and nitrogen-containing groups are noticed in the 3300 cm-1 region. The absorption band in the 1250 cm-1 region is attributed to the presence of C-O-C valence bonds. The absorption band in the 1600 cm-1 region is referred to stretching vibrations of C-C bonds in aromatic rings. The appearance of the absorption band at 1380 cm-1 is associated with terminal methyl groups. The absorption band at 1460 cm-1 corresponds to the asymmetric deformation vibrations of CH2 and CH3 groups. As will be seen from Table 2, Laprol, Sonpar, and Reapon contain the maximum number of terminal methyl groups. Unlike the other reagents, Sonpar and SNPKh 4880 D2 contain more functional groups of heteroatoms.

In Fig. 1, the shear rate is plotted against the shear stress at 20°C for crude oil I and its blends with 0.05% of various reagents. On the flow curves, three typical segments are distinguishable: the first segment corresponds to crude oil flow without destruction of the structure, the second, to highly plastic flow, and the third, to crude oil flow under high shear stresses whereupon the structure is completely destroyed and the oil exhibits Newtonian properties. At higher temperatures the oil flow becomes Newtonian. Similar mechanisms are typical for other blends of the oil as well.

Fig. 1
figure 1

Shear stress versus shear rate at 20°C for crude oil I (curve 1) and its blends with 0.05% of various reagents: 2 - Sonpar, 3 - Laprol, 4 - Neonol, 5 - Reapon, 6 - ETN-7r-14, 7 - IPG-12, and 8 - SNPKh 4880 D2.

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The viscosity of oil I and its blends with reagents is plotted against the shear stress in Fig. 2. At low shear stresses the viscosity is high perhaps because of phase transition in the asphaltene associates.

Fig. 2
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Viscosity versus shear stress at 20°C for oil I (curve 1) and its blend with 0.05% reagents: 2 - Sonpar, 3 - Laprol, 4 - Neonol, 5 - Reapon, 6 - ETN-7r-14, 7 - IPG-12, and δ- SNPKh 4880 D2.

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The influence of the reagents on the rheological properties of the crude oils is shown in Tables 3 and 4. It can be seen that Laprol exerts the best modifying effect on the oils. Reapon IF, ETN-7r-14, and SNPKh 4880 D2 raise viscosity of oil I. In terms of effectiveness of oil viscosity reducing action, the additives can be put in the following order: Laprol > Sonpar > Neonol > IPG.

Table 3  
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Table 4  
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Laprol is the best additive for oil II as well. The effectiveness of the reagents in this regard declines in the order: Laprol > Copolymer of ethylene with vinyl acetate > Neonol > Reapon > Sonpar.

The surface activity of the modifiers depends on the chemical nature of the side groups and the rate of their rearrangement along the main chain of the modifiers. Alkyl groups create steric hindrances, which hinder growth of paraffin crystals, their close contact, and formation of spatial structure. The inhibiting efficiency of paraffin wax deposits rises with increase in the number of methyl and methylene groups. Perhaps because of this, Laprol exerts the maximum modifying effect on the test crude oils. Note that the other functional groups in the reagent molecules were not found to have specific influence on the rheological properties of the oils.

Thus, the investigations conducted revealed that the maximum decrease in the dynamic viscosity of the test crude oils occurs in the presence of Laprol. The alkyl groups inverted to the hydrocarbon medium facilitate adsorption of the modifiers on the paraffin crystal surface. The more numerous they are, the stronger their modifying effect.