Study On The Relationship Between Dispersion Gel And Pore Throat And The Mechanism Of Regulation And Control

Dispersion gel is a kind of particle gel,which is formed by the crosslinking of crosslinked system on the ground,and it has the characteristics of small particle size,large quantity,good suspension and dispersion,high elasticity and wide application range.So dispersion gel has great potential applications in the field of deep profile control and oil displacement.At present,the application of dispersion gel is limited mainly due to the hard control about compatibility of particle and formation pore throat,in which gel particles frequently play a blocking effect for oil layers around water injection well,and water will soon flow around and enter into the high-permeability layers once again,causing the limited effect of deep profile control and flooding.Hence,in this paper experimental and theoretical studies were conducted on the basis of the matching relationship between dispersion gel and pore throat and profile control and oil displacement mechanism.In this study,micron-sized dispersion gel was prepared by inverse emulsion polymerization,and its basic physical and chemical properties were characterized.The gel particles had good sphericity,saline and thermal stability,expansion ability and viscoelasticity,as well as could be uniformly dispersed in water.Core flooding experiment,microporous membrane diafiltration device,SEM,laser particle size analyzer and ultraviolet spectrophotometer were carried out for investigating factors about the matching relation between dispersion gel and pore throat,analyzing the migration and retention mechanism of the dispersion gel and building the empirical mathematical models about the migration and plugging of the gel particle,which took into account matching factor,mass concentration,particle elasticity and seepage velocity.The results indicate that with the increase of the matching factor,the migration and blocking types of the dispersion gel were,in order,"smooth pass","low-efficiency plugging","high-efficiency plugging" and "complete plugging".With the decrease of seepage velocity or the increase of particle elasticity/mass concentration,the matching degree between the dispersion gel and the pore throat was improved;for the matching factor within an appropriate range,the gel particles with smaller matching factor but higher elasticity could exhibit a better sealing performance in the porous media.The migration and retention modes of the dispersion gel mainly included:? smooth pass,? deposition and release,? elastic blocking-remigration,in which elastic blocking could be subdivided into capture blocking,superposition blocking and bridge blocking,and remigration involved the following three processes:elastic deformation,stable migration/pass after crashed,elastic recovery.?complete blocking.The experimental results of 2D-visualization plate displayed the flow distribution,and quantified the area sweep efficiency and oil displacement efficiency of high,medium and low permeable layers under different displacement stages.The recovery degree of different pore throat intervals for different displacement stages from microscopic view was quantitatively analyzed and the effect of particle elasticity on oil recovery was investigated through nuclear magnetic resonance(NMR).Compared with the water flooding,both the right end point and the oil-water two-phase isotonic point of the relative permeability curves for dispersion gel flooding were shifted to the right;and disproportionate permeability reduced(DPR).The oil recovery improved with the increase of mass concentration or the decrease of seepage velocity.Based on above experiments,the profile control and flooding mechanism of dispersion gel could be summarized in the following five aspects.? Gel particles entered into high-permeability layers preferentially,attaining selective profile control and flooding.?Owing to deposition-release and elastic plugging-remigration of gel particles,the in-depth diversion could be achieved.?The oil film attached to pore-throat surface could be peeled off because of the elastic deformation of particles.The residual oil at the blind end could be squeezed out due to elastic recovery of particles.The breakthrough of gel particles from pore throat caused an instantaneous "negative pressure." ?Disproportionate permeability reduced(DPR).