Research On The Evaluation Method Of Polymer Microsphere Reservoir Adaptability And The Profile Control And Displacement Mechanism

Polymer flooding is an important technical means for oil development due to its simple technique,low equipment cost,and large increase in recovery efficiency.But in the late stage of polymer flooding,the oil displacement effect has been seriously affected by the “entry profile inversion” phenomenon,which is caused by the reservoir heterogeneity and polymer retention characteristics.Polymer microspheres have the characteristics of strong deformation ability and narrow distribution range of particle size.After coming into porous media,it shows the properties of “plugging large pore without plugging the small one” and the motion feature of “trapping,deformation,migration,re-trapping,re-deformation and re-migration”,which can slow down the process of profile inversion,and achieve the goal of deep fluid diversion and expand swept volume.In recent years,a series of field tests have been carried out in China,especially in the Bohai oilfield,which can increase oil production and reduce water cut obviously.Compared with the field test and application status,the evaluation method of polymer microsphere reservoir adaptability and the profile control and displacement mechanism is still in the initial stage.Therefore,it is urgent to study on the related methods and action mechanism.Theoretically guided by reservoir engineering,physical chemistry and biological fluid mechanics,by means of instrument detection,chemical analysis and physical simulation,this paper researched the physical and chemical properties of polymer microspheres,the matching relationship between particle size and pore throat,the migration and deep fluid diversion ability,the profile control and displacement effect and its mechanism,and the EOR technique of “well pattern adjustment and polymer microsphere injection” after polymer flooding.Results show that,polymer microspheres have well water swelling properties.They expand rapidly in the initial stage,then slow down,and finally tend to balance.The expansion multiple becomes larger with increase of temperature and the decrease of solvent water salinity.The microsphere type,mass concentration and core permeability has effect on the seepage characteristics and reservoir adaptability.With the increase of particle size and mass concentration,the resistance coefficient,residual resistance coefficient and permeability limit increases.When the mass concentration of polymer microsphere is 0.1%~0.3%,the “particle size / median pore diameter” ranges of SMG(W)and SMG(Y)are 0.79~0.84 and 1.73~1.78 respectively.Compared with the molecular clew size distribution of polymer solution,the particle size distribution of polymer microspheres is narrow.The inaccessible pore volume of microspheres is large,while the accessible pore volume of carrier fluid is large.As a result,the microsphere solution can generate the synergistic effect of blocking and flooding.The long core experiment shows that,polymer microsphere presents the motion feature of “migration,trapping,deformation,re-migration,re-trapping and re-deformation” in the porous media,which can realize deep fluid diversion,expand macroscopic and microscopic swept volume.The core displacement experiment shows that,under the condition of the same agent cost and constant pressure flooding,the oil increment and water reduction effect of microsphere flooding is much better than that of polymer flooding.The alternating injection method of “polymer microsphere and water” or “polymer microsphere and weak gel” can be used to slow down the severity of profile inversion or delay the reversal time,which is helpful to improve the chemical flooding effect.The three dimensional simulation model displacement experiments show that,the swept volume can be expanded by the microspheres injection or the well pattern adjustment after polymer flooding.The use of binary compound system(polymer microspheres and petroleum sulfonate)and ternary compound system(polymer microspheres,weak base and petroleum sulfonate)can achieve the dual goals of expanding the swept volume and improving oil displacement efficiency.