Currently, offshore oil exploitation widely uses polymer flooding techniques, which result in the produced fluid exhibiting non-Newtonian characteristics. This creates an urgent need for efficient and compact separators for oil–water separation in polymer-containing produced fluids. This study establishes a numerical model for T-junctions based on the Euler–Euler multiphase flow model, Reynolds stress turbulence model, and a non-Newtonian force model. It explores the effects of various operational parameters (such as inlet oil content, inlet velocity, split ratio, and oil phase density) and structural parameters (such as branch pipe angle and number of branches) on the separation efficiency of non-Newtonian oil and polymer solution two-phase flow in T-junctions. The results indicate that reducing the inlet velocity and decreasing the branch pipe angle can significantly lower the turbulence intensity within the main pipe, promote fluid stratification, and improve separation efficiency. Particularly, at a flow split ratio of 0.5, the separation efficiency peaks. Furthermore, a comparison between heavy oil–water two-phase flow and non-Newtonian oil and polymer solution two-phase flow disclose that the former achieves a maximum separation efficiency of approximately 87% under six branch conditions, while the latter shows poorer stratification and separation efficiency in the front section of the main pipe. By investigating the key factors affecting separation performance, this study provides theoretical support for the design and development of separation devices tailored to non-Newtonian polymer-containing produced fluids.

Most of the fluids encountered in the oil and gas exploitation process exhibit non-Newtonian fluid characteristics, which presents new challenges for the treatment of produced liquid. In this paper, the Eulerian multiphase model and the power law model were coupled to simulate the distribution characteristics of non-Newtonian fluid swirling flow fields in a vane-type separator. Larger oil droplets are able to migrate to the pipe center at relatively weak vortex intensities, which helps to accelerate the formation of the oil core. Due to the rapid decay of the vortex strength, the tangential velocity of the oil droplets drops more rapidly than that of the axial component, thereby reducing the axial energy loss. As the volume fractions of inlet oil increase, the oil core becomes more pronounced, but the convergence of the oil phase gets worse. During the migration, the interaction between dense oil droplets increases the viscosity of the non-Newtonian fluid and decreases the tangential velocity, leading to a maximum apparent viscosity at the center of the pipe. A higher vortex intensity tends to stabilize the vortex core, whilst higher flow velocities, which increases rotational velocities at the exit of the deflection section, deforms the vortex more severely. Moreover, higher inlet flow velocities contribute to better convergence of the oil cores. All these factors are important to better understand the smooth characteristics of non-Newtonian fluids and to provide a theoretical basis for future design and optimization of efficient separators.

Deep-sea minerals are regarded as the most economically viable and promising mineral resource. Vertical hydraulic lifting represents one of the most promising methods for deep-sea mining lifting systems. To mitigate the potential for clogging due to the aggregation of particles in vertical pipe transport during deep-sea mining operations, this paper employs numerical simulations utilizing the computational fluid dynamics and discrete element method (CFD-DEM) model to investigate the swirling flow transportation of mineral particles. The characteristics of the swirling flow field and the motion law of double-size particles at different swirling ratios are investigated. The findings demonstrate that, in comparison to axial transport within the pipeline, the particle movement observed in swirling flow transport exhibits an upward spiral trajectory. This phenomenon facilitates the orderly movement of particles, thereby enhancing the fluidization of particles within the pipeline. An increase in the swirling ratio (SR) has a considerable impact on the velocity within the pipe. The tangential velocity distribution undergoes a gradual transition from centrosymmetric to non-centrosymmetric as the distance from the inlet increases. An increase in the SR results in an enhanced aggregation of particles at the wall, accompanied by a notable rise in the local particle concentration. The value of SR = 0.3 represents a critical threshold. When SR exceeds this value, the distribution of particles in the cross-section reaches a relatively stable state, rendering it challenging to further alter the distribution and concentration of particles, even if the SR is augmented. Furthermore, the maximum local particle concentration in the vicinity of the wall tends to be stable. These results provide valuable insights into vertical pipe swirling flow transport for deep-sea mining.

In the process of oil production, wells containing gas can impact the efficiency of electric submersible pump (ESP), potentially causing gas lock. This issue can lead to the loss of lifting capacity in ESP, affecting the normal production of oil wells. To address this problem, the concept of gas separation before mixing transportation has been proposed, and a gas–liquid separation–mixing device has been designed. Experimental tests on the gas–liquid two-phase flow under various working conditions were conducted. A numerical model of the physical process was developed and validated with the experimental results. The results indicate that when the inlet flow rate exceeds 8.75 m3/h, the gas phase can be effectively accumulated in the center of the main pipeline after flowing through the guide vanes, thereby achieving efficient gas–liquid separation. Centrifugal number, which is defined as the ratio of axial flux of centrifugal force to axial flux of gravity, was proposed for evaluating the flow characteristics. When the centrifugal number exceeds 6.5, a high-quality gas core is formed in the pipe. At high inlet gas content, the volume fraction of gas in the main pipe initially decreases to 2% as the flow rate increases to 15 m3/h. However, at a flow rate of 30 m3/h, the volume fraction gradually rises to 30%, which results in a significant amount of gas being forced into the main pipe. The results are beneficial for expanding the use of ESP and improving the lifting efficiency in the development of oil field with high gas content.

With offshore oil and gas exploration advancing into ultra-deep waters, subsea reservoirs face extreme high-temperature and high-pressure (HTHP) conditions, leading to significant alterations in crude oil properties. These changes destabilize oil–water phase distribution and impair separation efficiency in swirl separators. Non-Newtonian fluid behavior under HTHP conditions, characterized by temperature-sensitive viscosity and shear-thinning effects, further modifies the rheological response and internal swirling-flow characteristics. This study establishes a computational fluid dynamics (CFD) framework integrating Eulerian–Eulerian multiphase modeling with power-law rheology. Simulations analyzed power-law fluid behavior across a temperature range of 30–210 °C, focusing on shear-thinning effects and phase distribution. The results show that the oil-core transport fraction increased from 0.162 at 30 °C to 0.194 at 150 °C and then decreased to 0.141 at 210 °C. Although the peak tangential velocity continued to increase with temperature, the strongest central oil-phase enrichment occurred at 150 °C, indicating that stronger swirl does not necessarily correspond to stronger phase segregation. These results provide mechanistic insight and a numerical basis for subsequent scale-up studies of HTHP guided-vane swirl separators.