The waxy crudes gelling and the wax depositing on the inner walls of crude oil pipelines present a costly problem in low-temperature transportation processes. This study focuses on a physical understanding of the gelling deposition during flow of two-phase oil–water in the pipelines. A method for evaluating the gelation characteristic of two-phase oil–water is established, and the effect of emulsified water on gelation is discussed. As the physical properties description, the two-phase diffusion coefficient is found to be a strong function of the water cut. The potential models developed from single-phase flow wax deposition models are proposed spontaneously, and the deposition behavior of two-phase flow in pipelines is predicted under a range of flow conditions in low-temperature transportation. The predictions show that the gelling deposition rate of two-phase oil–water flow is closely related to the pipe flow temperature, external temperature, water cut, and flow rate. The mechanisms of kinetic resistance for diffusion and gelation nucleation related to emulsification are non-negligible under the low-temperature condition. The prediction models are then verified by deposition experiments that are conducted in the laboratory flow loop. This study is not only beneficial to provide a robust and rigorous way to predict two-phase oil–water gelling deposition under the condition of the low-temperature transportation but also significant to well understand the deposition process in oil–water flow. Besides, the study further accelerates the simplification and optimization of petroleum industry production engineering as well.

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With the progresses of industrial scale of high concentration and high molecular weight polymer flooding in Daqing oilfield, there are severe polymer plug problems, which occur in the perforated zone and the interstices of the formation adjacent the perforated zone. In attempts to remove or at lease reduce these polymeric build-up plugs, the strong oxidants are widely used in oilfields. The use of oxidants is undesirable because of the high price and short efficient period. What is more, it cannot meet standards of safety and environmental protection. This article presents lab and field test results of this removing polymeric plug method based on microbial degrading polymer. Lab experiments results show that polymers with different molecular weights were efficiently degraded by screened bacteria under different reservoir temperatures. It can be seen in visualization model that polymer plugs in pore were removed obviously. The polymer injection pressure was decreased 25%. The pilot tests in Daqing oilfield showed that by applying the method, average injection pressure of each well was decreased 435 psia, the average effective period reached to 520 days, and more than 7,000 barrels (bbl) of oil were increased in the test field.

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.