| Microspheres are currently used in a variety of profile control and water shutoff products.Generally,microspheres are small in size and can be expanded several times in a short period of time.After being injected into the formation,they are easy to ent er the deep part of the formation.After the microspheres are expanded,they can block the pores of the formation;these characteristics make the microspheres can be used as profile control and water plugging agents.It is used in all major oil fields.Although using microspheres to improve oil recovery is nothing new now,but the complex formation environment limits the use of microspheres day by day.The existing polymer microspheres have a rapid rate of water absorption and volume expansion after encountering water,which affecting the migration depth in the formation.Under the influence of temperature and salinity,the performance and function will be poor.For low-permeability or ultra-low permeability formations,micron-sized microsphere particles are still large,that is to say,in low-permeability or ultra-low-permeability formations,micro-scale microspheres are generally difficult to play as ignificant role.In order to solve the above problems and reduce the particle size of the microspheres,delay the water swell expansion rate of the microspheres,improve the temperature resistance,salt tolerance,and enhance the shear performance and viscoelastic properties,the following research was carried out:The oil phase solution was prepared by adding 3#white oil as a dispersion medium,adding emulsifier sorbitan oleate?Span-80?and polyoxyethylene?20?ether sorbitan monooleate?Tween-80?.In order to make the reaction proceed faster,azobisisobutyron itrile?AIBN?was added to the oil phase.A certain amount of acrylami de?AM?,N,N-methylenebisacrylamide?MBA?,2-acrylamide-2-meth ylpropanesulfonic acid?AMPS?was dissolved in distilled water,and the pH was adjusted with sodium hydroxide.Adding the chelating agent disodium edetate?EDTA?to form an aqueous phase solut ion,The oil phase was mixed with the water phase,the oxygen was driven off under nitrogen,the reaction was initiated with ammo nium persulfate?APS?and sodium hydrogen sulfite?SHS?solution,The polymerized product was diverted with a diverting agent to obtain a polyacrylamide nanosphere emulsion,and this polymerization method was a reverse microemulsion polymerization method.The optimum conditions for the reaction were determined by single factor method:oil to water ratio of 6:4,monomer concentra tion of 25%,monomer ratio of AM:AMPS:MBA of 74:20:6,emuls ifier ratio Span-80 and Tween-80 were 8:4,the stirring rate was 350 r/min,the initiation temperature was 25?,the initiator addition amount was 0.3%,and the pH was 6.8.The size and morphology of the microspheres were characterized by fourier transform infr ared spectroscopy,nano-laser particle size analyzer,transmission el ectron microscope,high-resolution field emission scanning electron microscopy and thermogravimetry.The test results showed that the prepared nanospheres have a good structure,the particle size is47.23nm,the size is small,the spherical shape is regular,the particles are uniform,and the thermal stability is good.The performance of nanospheres was evaluated by rheometer,interfacial tension meter,stability analyzer,water absorption testd evice,etc.The test results showed that the nanospheres had a lon ger shelf life,and the water absorption ratio was 4.45 times after7 days of water absorption.The water multiplication rate and wa ter absorption ratio are similar.Under the influence of salinity an d temperature,the interfacial tension can be less than 1.0×10-3mN/m,and the expansion ratio after expansion for 5d in distilled water is 4.02 times,after 2.0×104mg/L mineralization.The underwater expansion ratio is 3.16 times,the viscosity of the nanosphere solution is small,and the viscosity of the microsphere solution is significantly reduced during shearing.The viscoelasticity test indicated that the elasticity of the microsphere is greater than the viscosity and can be elastically deformed.The performance of the micros pheres is good and achieves the pre-set goals.The application per formance of nanospheres was investigated by testing the injectability,plugging and profile control of microspheres in the core.The test results showed that the nanospheres had a good injection perfo rmance and the blocking rate was more than 95%in low permeability core,it had a good profile control effect.It can increase oil production and reduce water production,nano microspheres have good application performance.Through the preliminary investigation,the performance of the nano-microspheres is better.After the pilot scale-up,various perf ormance tests on the nano-sphere products of the pilot test were carried out.The results showed that the performance of the pilot-scale products was good,consistent with the performance of the sample prepared by the laboratory,polyacrylamide nanospheres succe ssfully achieved industrial production.After field application in different blocks of ultra-low permeability reservoirs,the results showed that polyacrylamide nanosphere products can increase single well productivity,reduce water content of production fluid,and have a higher effective ratio of oil wells after injection,which can in crease water injection pressure and increase the water absorption thickness of the injection well makes the water absorption profile more uniform,which can increase the formation pressure and achieve stable oil control.The field application results showed that the application effect of polyacrylamide nanospheres was good,and the recovery of ultra-low permeability oilfield was improved.It has played a significant role in improving oil recovery in ultra-low permeability oilfields. |
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