2.2.1. Oil Sample’s Freezing Point Determination
Within the study, a temperature range of 0–60 °C was chosen for all experiments to align closely with the actual reservoir conditions of taken oilfield samples. Throughout the analysis, oil reservoirs had a temperature of overall 50 °C. By water injection, this temperature could be lowered, promoting asphaltene deposition. As oil is produced and transported through the wellbore, the temperature changes further, increasing the possibility of asphaltene precipitation due to reduced solubility at lower temperatures.
In laboratory conditions, the freezing point of oil examples without and with reagents was determined according to RD 39-3-812-82 methodology [
12]. A 100 mL volume of oil sample was poured into spherical test tubes with a diameter of 20 mm and a height of 160 mm, then heated to a temperature of 55–60 °C. Chemical compounds of various concentrations were added to it, and the mixture was gradually cooled to a temperature of 30–40 °C (for conducting comparison, one test tube had no added chemical compound). Then, the test tubes were placed in the thermostat, and the cooling process was continued. As the temperature gradually dropped, precise measurements were taken at intervals of every three degrees Celsius. At each interval, the test tubes were tilted to a 90° angle to ensure uniform distribution of the oil within the tube. In successive inspections, the temperature at which the level of oil in the test bottle became stationary was noted, and at this time, the test bottle was kept in a horizontal position for 5 s, and the complete solidification of the liquid was determined due to the immobility of the upper liquid layer [
13] (
Figure 1).
2.2.2. Determination of Oil Deposit Quantity
The aim of the “cold finger test” method is to determine the quantity of asphaltene-resin-paraffin substances deposited from oil on a cooled metal surface. In the “cold finger test” method, all stages such as the formation and accumulation of ARPD, including processes such as sediment dispersion due to oil flow effect, the precipitation, growth of heavy components of oil, paraffin crystals and the crystallization center formation are realized.
The studied oil samples with a volume of 100 mL were s poured into chemical metal cups with the same proportion (d = 36 mm, ℓ = 130 mm) equipped with a magnetic stirrer intended for the experiment (
Figure 2). Then, the oil in the chemical cups was heated to 50–55 °C with stirring at 350 rpm using a magnetic stirrer to ensure a good reagent distribution throughout the oil volume, and a pre-calculated amount of the chemical compound was added to each sample (chemical compound was not added to one of the cups intentionally for comparison purposes). The chemical cups were placed in an external thermostat, and a stainless-steel U-shaped tube (d = 15 mm, ℓ = 110 mm) was inserted into each. The “cold finger” surface provides a temperature gradient with the liquid, which is perfect for the precipitation and crystallization of high-molecular oil components. The asphaltene-resin-paraffin precipitations were liquefied by heating the “cold finger” to 70 °C using a cryostat, and the precipitation mass was measured using the gravimetric technique [
14]. The experiment duration was 40 min.
2.2.3. Determination Method for Effective Viscosity, Limiting Shear Stress and Non-Newtonian Index
The method was implemented by using a rotational viscometer, brand of the “Rheotest 2.1”, or its subsequent modifications with measuring devices—a special cylindrical cone-plate (
Figure 3).
Prior to experimentation, the sample fluid was prepared while maintaining its temperature and purity. The viscometer was calibrated meticulously according to manufacturer guidelines, and precise temperature control mechanisms were employed. Initial torque and rotational speed readings were recorded before gradually increasing the rotational speed, recording torque at each increment to cover a range of shear rates. Rigorous data analysis techniques were applied to calculate the shear rate and subsequently determine the effective viscosity. In laboratory conditions, the research process was carried out in a wide temperature range (0, 10, 20, 30, 40 and 50 °C) in the “Rheotest-2.1” viscometer with 100 mL of oil samples. The experiment duration was 2 h. According to device results, the non-Newtonian index was determined and processed. Within the framework of the Gersel–Balkley model, the value of the effective viscosity depending on the temperature was calculated by the following expression [
15]:
μ
e—effective viscosity, Pa·s, τ—shear stress, Pa, τ
0—limit shear stress, Pa, γ—velocity gradient, s
−1, K—consistency, (Pa·s), (the higher liquid viscosity means the greater K value), n—non-Newtonian index, (the more n is different from 1, the more non-Newtonian properties increase).
2.2.4. Corrosion Rate Determination by Gravimetric Method
Assessing reagents’ effectiveness in inhibiting corrosion is crucial for understanding their potential to reduce metal corrosion rates in various aggressive environments, helping optimize the reagents for industrial applications, where material durability and reliability are key factors. The essence of the gravimetric test method is based on determining the mass loss of metal samples during their stay in the tested corrosion environment. In laboratory conditions, gravimetric tests are carried out in accordance with the requirements of relevant methodology [
16,
17].
During the experiment, the samples used are prepared in the form of plates from different steel brands with 100 mL volume of reagents. The duration of the experiment is 10–12 h. The average static relative error of the measured steel sample corrosion rate is not higher than 0.5%. Ct20 steel samples, with dimensions of 30 × 20 × 1 mm, were used during the research.
Table 2 shows the chemical composition of Ct20 brand steel.
To determine the corrosion rate by the gravimetric method, firstly steel samples are prepared by cutting, shaping and cleaning them with sandpaper and acetone, then drying and accurately weighing each sample to record the initial mass (m
0). The samples were submerged in a prepared corrosive solution for a specified duration, ensuring they were fully immersed and maintained under consistent environmental conditions. After the exposure period, the samples were removed, rinsed with distilled water, cleaned to remove corrosion products without affecting the base metal, dried thoroughly, and reweighed to obtain the final mass (m
1). The area of the samples taken for testing was calculated according to the following formula:
Sn—area of steel sample, mm
2, a—length of sample, mm, b—width of sample, mm, h—height of sample, mm.
Since a = 30 mm, b = 20 mm, and h = 1 mm, the area of the steel sample for testing was determined as SN = 2 × 30 × 1 + 2 × 30 × 20 + 2 × 20 × 1 = 1300 mm2 = 0.0013 m2.
Metal loss was calculated for three steel plates, and the average mass was found. During gravimetric tests, the corrosion rate mass indicator in conditions both without reagent and with reagent was characterized by K
m and calculated by the following mathematical equation:
K
m—corrosion rate mass index, g/m
2·h, m
0—mass of the sample before the tests, g; m
1—mass of the sample after the tests, S—average surface area calculated for three samples, m
2; τ—duration of the test, h.
The protection effect of reagent was calculated as
Z—protection effect, %, K
0—corrosion rate without reagent, g/m
2·h, K
inh—corrosion rate with reagent, g/m
2·h.