**5. Problems of improving rheological properties in Refining heavy crude oil**

Heavy oils, due to their high content of heavy components (65–70% of fractions >350 boiling point) exhibit the visco-plastic properties of non-Newtonian oils. Currently, there are no special technologies for processing heavy oils, except for some works [29, 30], because their processing is limited by problems of oil transportation in pipes, pumps, heat exchangers, and other equipment.

The viscosity of heavy oils, which determines their fluidity, depends on the content of asphalt-resinous substances, paraffin, water in the oil, and other factors. **Figure 11** shows experimental data on changes in viscosity of West Siberian oil depending on asphaltene content [31].

The existence of a spike in oil viscosity *ϕ* ¼ 0*:*3 when confirmed by flowstructuring phenomena that degrade the rheological properties of the oils. When refining heavy oils in operating plants at relatively low temperatures, the effective viscosity of the oil increases, which contributes to a decrease in its flowability and, in general, the productivity of the process. The reduction in viscosity of heavy oils, which ensures their transportability, depends on two factors: increasing their temperature and diluting them with lighter components.

In this regard, the main factor for improving the rheological properties of oil and its refining conditions in solving practical problems is to increase the temperature of the oil feedstock at the inlet to the unit and partially dilute it by creating recirculation of the lighter component to mix with the crude oil (**Figure 12**). This intensification of the refining process solves both problems simultaneously. Process of primary processing of oil is carried out by its preliminary heating to the certain temperature with its intermediate purification from water and salts, containing in oil, in the dehydrator 4 and the further separation in a mass-exchange rectification column 5.

A Kazakhstan heavy paraffinic oil with high viscosity was used in the installation. In order to improve the rheological properties and viscosity of the crude oil, a portion of the fraction >240°C. From column 5, the oil is returned back to mix with the crude oil after pre-cooling to pump 2. Creating a recirculation system allows for reducing the kinematic viscosity of the crude oil by increasing its temperature to 20–25°C and diluting it with lighter fluid. Experimental studies have shown a significant effect of the amount and temperature of fraction >240°C on the effective viscosity of the crude oil (**Figure 13**).

As **Figure 13** shows, the viscosity of the oil decreases as the temperature and the amount of fraction added increase. An expression describing the change in kinematic viscosity of oil with temperature at different fractional contents >240°C, can be represented as

$$v = 108.95(1 - 2.17\phi) \exp\left(-0.028T\right) \times 10^{-6} \tag{36}$$

here *ϕ* ¼ *mR=*ð Þ *m*<sup>0</sup> þ *mR* - is the mass fraction of fraction > 2400C in crude oil, *m*0, *mR* - mass flows of crude oil and fraction.

#### **Figure 11.**

*Dependence of effective viscosity on asphalt-resin content at temperatures: 1–84°C; 2–112°C; 3–144°C ( area of discontinuous structure formation).*

#### **Figure 12.**

*Scheme of primary oil refining with recirculation: 1-mixer; 2-pump; 3-heat exchanger system; 4-dehydrator; 5-distillation column; 6-cooler; I- crude oil; II-recirculation line; III-fraction >240°C.*

Recirculating some of the lighter refining fraction with higher temperature and lower viscosity to mix with the crude oil reduces the viscosity of the oil by increasing its temperature and partially diluting it with the lighter fraction (**Figure 13**).

#### **6. Discussion of results**

The problems of the rheology of non-Newtonian oil, accompanied by physical phenomena of formation and destruction of coagulation structures and aggregates, significantly affecting the flow have been considered and analyzed. Have been considered the issues of hydrodynamic interaction of particles leading to the formation of disordered structures that significantly change the rheological properties of non-Newtonian oil.

*Applied Problems in the Rheology of Structured Non-Newtonian Oils DOI: http://dx.doi.org/10.5772/intechopen.105948*

#### **Figure 13.**

*Dependence of kinematic viscosity of oil on temperature at its content of fraction >240*<sup>0</sup>*Cφ (mass fraction) equal to: 1–0.3; 2–0.25; 3–0.20; 4–0.15; 5–0.10; 6–0.05. <sup>ν</sup>* <sup>10</sup>4, *<sup>m</sup>*<sup>2</sup>*=s.*

It is noted that the use of aromatic hydrocarbons to dissolve asphalt-resinous substances leads to improved rheological properties of heavy oil.

This section has considered some of the challenges in improving the rheological properties of non-Newtonian oils, both in gas lift production and transportation, and refining. Obviously, there are other ways to improve the rheological properties of oils containing high concentrations of asphalt-resinous and paraffinic substances, solidphase particles, and dispersed water.

#### **Nomenclature**


#### *Advances in Rheology of Materials*

