Research On Mechanism And Adjustment Technology Of Viscosity Loss For Displacing Fluid In Polymer Flooding

Development of tertiary oil recovery technology is not only related to the stable and increased production of my country's oil fields,but also an important issue involving national energy strategy and energy security.At present,the most suitable mining technology for terrestrial heterogeneous oil reservoirs in my country is polymer flooding technology,which increases the displacement phase displacement range by increasing the displacement phase viscosity to reduce the water-oil mobility ratio,thereby improving oilfield recovery.However,the viscosity loss of the oil-displacing polymer during the mining process,especially the viscosity reduction of the displacement fluid caused by mechanical shear degradation,results in the displacement efficiency not reaching the expected effect.The rheological behavior of the displacement fluid in the formation is also unclear,and further increasing the displacement range of the displacement fluid and oil recovery efficiency is also the bottleneck of the tertiary oil recovery technology.Therefore,in this paper,the following research work was carried out on the problem of viscosity reduction due to mechanical degradation,which caused the most significant viscosity loss of polymer flooding,and the bottleneck problem of displacement technology development.Aiming at the flow field of the static mixer that caused the most significant mechanical degradation of the displacement fluid in the polymer injection well surface system,we used a combination of simulation analysis and theoretical research to analyze the factors influencing the mixing efficiency and shear action of the static mixer.After that,we proposed a new parallel continuous multi-helical static mixing unit structure,and at the same time established a static mixer flow field mathematical model.By comparing the mixing flow field and shear flow mechanism of the three static mixers,we optimized the new static mixing geometry parameters.We evaluated the mixing and viscosity reduction performance of the new static mixer through indoor and oilfield wellsite experiments.The results show that the new static mixing ensures that the mixing effect meets the engineering needs.Moreover,the average viscosity loss rate is only 3.0%,which is 3.8 percentage points lower than that of SMX and Kenics static mixers.Aiming at the flow field of the injection throttle valve core which causes the most severe mechanical degradation of the displacement fluid in the downhole system of the polymer injection well,we use the method of combining simulation analysis and theoretical research to analyze the factors affecting the pressure regulating and shearing effect of the throttle valve core of the injector.We have proposed a streamlined multi-stage pressure regulating throttle spool structure,and established a multi-stage throttle spool flow field mathematical model.By comparing the streamlined and rectangular spool flow field pressure regulation and shear flow mechanism,we can understand that the streamlined spool can have the same pressure regulation effect as the rectangular spool,and the maximum shear rate is reduced by 55.6%compared with the rectangular spool flow field.We evaluated the pressure regulation and viscosity reduction performance of the streamlined throttle spool through laboratory experiments.The results show that the streamlined spool not only can ensure the pressure regulation effect to meet the needs of the project,but also its viscosity loss rate under the maximum working flow rate is less than 3%,which is 9%lower than that of the rectangular valve core.Based on the flow mechanism of the micropore throat flow field in the porous media of the reservoir,we established a coupling model of polymer adsorption behavior and shear flow.Then we used the research method combining simulation analysis and experiment and compared the shear action strength of the shrinkage hole throat and the capillary wall.Finally,we studied the apparent rheological behavior in the microporous throat flow field and analyzed the shear degradation mechanism of the oil displacement polymer at low injection flow rates.Simulation analysis and experimental results show that the polymer solution undergoes mechanical degradation at low flow rates,which verifies the correctness of the adsorption and shear coupling model.Based on the mechanism of microporous throat shear degradation,we propose a method for calculating the amount of polymer adsorption in microchannels.This method can replace the measurement of the solution concentration value of microscale by measuring the dynamic viscosity of the sample,which greatly reduces the difficulty of measurementBased on the Maragoni flow mechanism,we used a combination of simulation analysis and experiment to study the directional movement and clustering behavior of polymer droplets.Then we established a two-phase flow mathematical model of the oil phase environment and polymer droplets,and provided driving forces for the polymer droplets based on the thermal capillary effect and the solute capillary effect,respectively.The driving trigger principle is that the interfacial tension of the two phases will decrease with increasing temperature or ion concentration.Therefore,when the heating phenomenon occurs locally on the side of the oil solvent,the fluid at the interface between the oil solvent and the air will flow to a low temperature,so the polymer droplets at the bottom of the container will move toward the heat source under the action of Maraconi flow.And the water phase droplets of the isotropic semiconductor Fe₂O₃nanoparticles,H₂O₂solution and polymer solution mixed will undergo a photo-Fenton reaction on the side irradiated by light,resulting in an ion concentration gradient inside the droplets.Since the liquid at the interface will flow from the area with high concentration to the area with low concentration,and the Maragoni effect will cause a cyclic flow within the droplet,the final aqueous droplet will move in the direction of the light source.This method can endow the displacement phase with self-propulsion ability,so it is expected to be used to expand the displacement area of the displacement fluid and improve the macroscopic displacement efficiency of the reservoir.In summary,this paper has carried out in-depth research and exploration on the shear viscosity loss mechanism of the reservoir polymer flooding injection system and methods to improve the reservoir displacement efficiency.The above research provides theoretical and technical support for polymer flooding to break through the technical bottleneck and further improve the recovery factor.