| The polymer microspheres have the characteristics of small initial particle size,excellent swelling performance,simple process flow and excellent sealing ability,and have great application potential in the field of deep oil control in oil fields.This study is aimed at poor application performance of plugging agents in deep osmotic flooding in low permeability reservoirs,Nano-micron polymer microspheres with concentrated particle size distribution,high strength,suitable expansion performance,high effective component content and good regulation and drive performance were designed and synthesized.The acrylamide(AM)was used as the monomer,the white oil was used as the dispersion medium,and the Span80/Tween80 was used as the composite emulsifier to prepare the inverse microemulsion.In the reverse microemulsion,the monomer aqueous solution accounted for 38.0%,the dispersed phase accounted for 45.0%,and the Span80/Tween80composite emulsion system with a mass ratio of 3:1 accounted for 17.0%(based on the total mass of the system).Using ammonium persulfate/sodium bisulfite(APS/SHS)redox system as initiator,N,N-methylenebisacrylamide(MBA)as crosslinking agent,Polyacrylamide microspheres were synthesized using reverse microemulsion polymerization.Optimization and selection of synthesis conditions with high conversion rate and high swelling ratio,The optimum synthesis conditions were determined as follows:the polymerization initiation temperature was 40?,the initiator and crosslinking agent addition amounts were 0.50%,040%(by mass of the monomer),and the stirring rate was 800 rpm.The final synthesized microsphere system is stable,the conversion rate is higher,reaching more than 75%,the particle size distribution is narrow,the particle size(D50)is 72 nm,and the swelling ratio of swelling in simulated formation water for 24h is 162.In order to prove the feasibility of its application in deep reservoir with low permeability,the physical properties,morphological characteristics,structural composition,thermal stability,effective content,rheological property and swelling property of polyacrylamide microspheres were characterized and evaluated.The synthesized polymer microsphere system is a light yellow transparent liquid which is completely dispersed in moisture,free from flocculation and precipitation,and has a density and viscosity at 25?of 0.962 g/cm~3 and1728 mPa·s,respectively.Morphological characterization shows that the shape of the polymer microspheres is regular,the sphericity is complete,the monodispersity is good,and the particle size distribution is narrow,about 70 nm.In terms of performance testing,the polymer microsphere system has a high effective content of more than 20%,and has good thermal stability,in line with relevant use standards,and the polymer microsphere system also has good injectability and swelling properties.The sand-filled tube flooding experiment was carried out in the laboratory.The experimental results show that the polymer microspheres can effectively block the dominant channel of the water flow,and continue to deepen along the pore channel,eventually playing the role of deep regulation.The injection parameters of polymer microspheres were optimized,and the results showed that the injection volume was 0.5PV.The injection concentration was2000 mg/L.With an injection rate of 0.3 mL/min,higher recovery can be achieved.In order to further improve the polymer microsphere flooding ability,the injection process of polymer microspheres is also optimized.that the medium-mass concentration medium slug injection process has the advantages of high-quality concentration short slug and low-mass concentration long slug,which is the best slug process.Compared with continuous injection,batch injection has longer action time and higher utilization efficiency of microspheres.It is the best injection method,and the optimized recovery process can achieve higher recovery efficiency. |
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