Capillary hysteresis significantly affects oil displacement efficiency in porous media by influencing residual oil trapping, relative permeability scanning behavior, and saturation history-dependent flow resistance. This paper evaluates core-scale EOR strategies designed to influence capillary trapping and saturation-history-dependent displacement behavior, with the aim of increasing displacement efficiency using sandstone core samples representing seven parent-core materials. Reservoir conditions were simulated through conventional high-salinity brine flooding, low-salinity waterflooding (LSWF), chemical EOR using alpha olefin sulfonate (AOS) surfactant, and low-salinity water-alternating-gas (WAG) flooding with nitrogen. After LSWF, separate batches of core samples were retrieved from the remaining material of the respective parent cores C1 to C7. Thus, the CEOR and N₂-WAG operations were conducted on different core samples that were separately processed and initialized. HSWF recovered an average of 53.15 ± 5.42% of OOIP at 56,300 ppm salinity and left a residual oil saturation of 34.57 ± 2.99% pore volume (PV). Among the brines examined, 7600 ppm provided the highest recovery of 61.31 ± 5.69% OOIP and left a residual oil saturation of 28.52 ± 3.36% PV. With further dilution of the brine solutions, performance decreased to 54.50 ± 5.96% OOIP recovery at 3000 ppm and 49.00 ± 6.24% OOIP at 1000 ppm. Further tests showed even worse results due to increasing solid content in the effluent, permeability impairment, and swelling of cores. Volume-weighted mean effluent solids content was 13.99 mg/L at 7600 ppm, 95.01 mg/L at 3000 ppm, and 225.00 mg/L at 1000 ppm. Micro-CT imaging of C1 for 3000 ppm pre- and post-flood cores indicated localized restriction of the resolved pore space. These results show that swelling and migration of fines contributed to the adverse responses at the lowest salinity. In contrast, a 0.5 wt% AOS formulation on a commercial-product basis (0.195 wt% active AOS) recovered 69.30 ± 6.32% OOIP with a residual oil saturation of 22.60 ± 4.00% PV, while N₂-WAG recovered 73.06 ± 6.23% OOIP with a residual oil saturation of 19.82 ± 4.01% PV. Consequently, the overall outcomes correlate with less residual trapping and better displacement under salinity control, interfacial-tension reduction, and cyclic gas–water saturation changes.

Relevance. High-paraffin, resinous crude oils are characterized by high viscosity and elevated pour points, which become particularly problematic under low-temperature conditions. These properties significantly complicate pipeline transportation due to increased hydraulic resistance, higher energy consumption, and flow instability. Therefore, improving the rheological properties of such oils is essential for ensuring efficient and reliable transportation. Effect of a magnetic field treatment and depressor additives are considered promising methods for viscosity and pour point reduction. Aim. To investigate the individual and combined effects of magnetic field treatment and the depressor additive Difron-3907 on the rheological properties of high-paraffin, resinous crude oil; to determine the optimal effect of a magnetic field exposure time, the effective additive concentration, and the efficiency of their combined application. Methods. Laboratory experiments were conducted using a Reotest viscometer. Oil viscosity was measured before and after effect of a magnetic field treatment and the addition of Difron-3907 at concentrations ranging from 100 to 700 ppm. Effect of a magnetic field exposure times varied between 5 and 25 minutes. The physicochemical properties of the crude oil sample were initially determined, and long-term viscosity stability was monitored over 25 days under optimal treatment conditions. Results and conclusions. 25-minute effect of a magnetic field treatment reduced oil viscosity from 2200 to 1000 mPa·s, corresponding to a 54.5% decrease. The addition of Difron-3907 at an optimal concentration of 700 ppm resulted in a viscosity reduction to 1210 mPa·s (approximately 45%). The highest efficiency was achieved through combined treatment: a 20-minute effect of a magnetic field exposure together with 350 ppm Difron-3907 reduced viscosity to 600 mPa·s, representing a 72.7% decrease. These findings demonstrate that the combined application of effect of a magnetic field waves and Difron-3907 significantly enhances the rheological properties of high-paraffin, resinous crude oils, contributing to reduced energy consumption and improved efficiency of pipeline transportation processes. For citation: Gurbanov G.R., Akhundova N.R. Investigation of the synchronous effect of a magnetic field and a depressor additive on the rheological parameters of high-paraffin crude oil. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, 2026, vol. 337, no. 8, pp. 129–139. http://doi.org/10.18799/24131830/2026/8/5438