While water exists in the waxy crude oil, gelling process of this non⁃Newtonian oil⁃water two⁃phase system not only has the properties of waxy crude oil but also its own specific characteristic as decrease of temperature. Both the gelling temperature limit and change rule of gelling strength in W/O waxy crude oil emulsion system under different emulsified water fractions, were investigated by rheological measurement. The results indicate that the characteristic gelling temperature and the strength of the gels increase with the increasing of emulsified water fraction, when the temperature decreasing at a certain rate; the gelling temperature in W/O waxy crude oil emulsion system of any given emulsified water fraction rises with the increasing of cooling rate, while the gelling strength decreased with the cooling rate rising under the constant pressure. The research results of the effect of emulsified water on the gelling characteristic for waxy crude oil at cooling process provides necessary support for the development and application of flow technology for multiphase transportation.

Based on the dissolved⁃air flotation process, a multiphase flow mixture model numerical simulation was established to simulate the pressure field distribution, particles trace characteristics and the removal effect of oil and suspended matter in the process of settlement separation of produced water by air flotation, the influence of air flotation on the characteristics of the settlement separation flow field of produced water is revealed by comparing with the characteristics of conventional gravity settlement separation. The results indicate that the more stable pressure field distribution is obtained by the sedimentation with dissolved⁃air flotation through adapting the change of treatment amount, and relatively stable and orderly motion tracks of oil droplets and suspended particles with uniform distribution in the flow field are obtained by avoiding vortexing. The removal rates of oil and suspended solids under simulated conditions are increased by 8%~11% compared with the conventional gravity sedimentation separation, and the improvement of the settlement separation effect of produced water was effectively ensured. The construction of the adaptability of air flotation process and the basis of improving the efficiency of produced water treatment are provided by the understanding of the flow field characteristics in the settlement separation of air flotation.

It was proposed that the advanced⁃treatment of polymer⁃flooding produced water and realized the re⁃injection requirements. The feasibility and potential of further deep filtration treatment of wastewater containing polymer after ordinary treatment were studied by numerical simulation. The available advanced⁃filtration process pattern was established and optimized based on the distribution of oil droplets and suspended solid particles, the concentrations oil and suspended solid in filtered water, and the removal rates of oil and suspended solid. The results indicated that the advanced⁃filtration process pattern with "double graded⁃media + three graded⁃media" could further improve filtration performance depended on hydraulic and interfacial effects. The removal rates of oil and suspended solid reached 87.78% and 87.11%, respectively. The oil content and suspended solids of filtered water were controlled within 5 mg/L required for deep water treatment. This is a potential filtration process model for advanced treatment of polymer⁃containing wastewater, and also provides a basis for effectively dealing with water quality problems in tertiary oil recovery by chemical flooding in oilfields.

Surfactant/Polymer (SP) combination flooding is an effective method to enhance oil recovery of high quality reserves,while its surface produced liquid treatment technology and the simplification and optimization of operating parameters are both still a challenge for the promotion of the chemical flooding technology industrialization.In this paper,the emulsification of SP combination flooding produced liquid is characterized by multi⁃factor perpendicular experiments,and then the effect factors of demulsification and dehydration are studied.Significant test results indicated that,compared with the temperature and water cut,the effect of the concentration of surfactant and polymer in the produced liquid on dispersivity and electronegativity of the bulk was lower,which showed the greater contribution to emulsification stability of produced liquid,thus the demulsification of the produced liquid was declined.Bottle test experiments indicated that a single mechanism of improving demulsification temperature or prolonging demulsification time couldn’t fundamentally improve the dehydration rate of the produced liquid and reduce the oil content in the water after separation,meanwhile,the improvement of the pH of the water phase and the strong shear effect of the flow field would further deteriorate the effect of demulsification,dehydration and the water quality after separation.

Granular layer filtration is widely used in the treatment system of oilfield produced water, and water distribution of granular layer filter which directly affects the purification effects of produced water plays the same significant role as the selection and arrangement of granular layer. The model of filter was built and unstructured grids were generated by Gambit. The flow rate field in the model was calculated by Fluent combined with DPM model. Based on the DPM model in Fluent software, a numerical simulation of pressure field distribution, filtration pressure drop along the axis, pathlines of particles, and particles distribution and aggregation behaviors were simulated and calculated. Then, water distribution characteristic in pressure filter of produced water was described, and optimization of water distribution process was realized. The results showed that the good performance of water distribution was obtained and the pressure drop in the filter with sieve tubes was reduced by 30.56% compared with the filter with slots. Furthermore, the filter with nine sieve tubes was optimized by its excellent water distribution characteristic. Such a numerical simulation method can provide effective support for optimization of filtration process and purification of produced water.