A wellhead multistage bundle gas–liquid separator combining a gas–liquid cylindrical cyclone (GLCC) with multi-tube bundle components is expected to improve the gas–liquid separation performance. However, there is no unified understanding of the factors influencing the separation performance of the separator. The continuous improvement and applications of the separator are restricted. This paper evaluated the performance of the separator using a numerical simulation method. The results indicate that the separation flow field evolves to be uniform with the increased water cut when the gas–oil ratio and flow rate remain constant. Compared with a 30% water cut, the separation efficiency at a 50% water cut increased by 5.88%. When the gas–oil ratio and water cut remained constant, the swirl effect of the primary separation was enhanced. The separation efficiency increased to more than 70% when the flow rate was 15 m/s. When the flow rate and water cut remained unchanged, the pressure of the separation flow field was reduced. However, when the gas–oil ratio was greater than 160 m3/t, the flow field trace density of the secondary separation bundle was reduced, and the separation efficiency was also lower than 60%. The separation efficiency can be further improved by optimizing the number and diameter of secondary separation bundles.

The produced water-containing polymer brings new challenges to oil-water separation in oilfield production, yet separators with coalescing plates to remove free water have been playing an active role. In this paper, the flow-field characteristics of polymer-laden produced water in a separator with coalescing plates are analyzed using computerized mathematical methods to investigate the effects with a water content of 55%, 70%, and 85%, flow rate of 3500 m3/d, 4800 m3/d, and 6000 m3/d, and duration time of 20 min, 40 min, and 60 min on flow-field properties and separating efficiency are studied. The results show that the separating efficiency is positively correlated with water content and duration time, and duration time has the greatest improvement to the separating efficiency, but the enhancement of flow rate may reduce the separating efficiency. It is also observed that the separation efficiency of free-water reached 70.9% and the water content at the oil outlet of the separator reached 20.4% at a duration time of 60 min, when the contained polymer concentration and water content in the oil-water mixture are 500 mg/L and 70%, respectively.

Although the problems of wax deposition in multiphase transportation pipelines have been addressed and wax deposition models have been developed in recent years, the complex wax deposition paths derived from the potential variety of flow regimes in multiphase flow have not been well understood. This study presented a method for characterizing wax crystals aggregation and developed a model for describing the wax deposition path in oil−water two-phase flows. The effect of the emulsified water droplets on wax crystals aggregation in shearing flows was identified using the polarized light microscopy and image analysis method. The role of the emulsified water droplets in the wax deposition path reaching the upper side and lower side of the pipeline wall was discussed by solving the developed model which involves the possible inclination angle of the multiphase transportation pipeline. The availability of the mechanistic model was validated by the data and knowledge in the existing literature. The results indicated that the circular degree and particle size of wax crystals showed a characteristic that it first increased and then decreased with the accumulation of emulsified water droplets in shearing flow, and this transition appeared to the phase inversion point of the oil−water two-phase. The wax deposition path was complex in multiphase transportation. The velocity for wax crystals depositing to the pipeline wall decreased, and the time for wax crystals depositing to the pipeline wall extended with the existence of emulsified water droplets. This behavior became remarkable when the dispersion stability of the oil−water two-phase enhanced.