Study On Oil Displacement Mechanism And Seepage Law Of PPG/ Polymer System

After years of water flooding or polymer flooding in Daqing Oilfield,the heterogeneity is more serious and the scope is constantly expanding,and dominant seepage channels appear between injection-production Wells.In view of the physical properties and fluid flow characteristics of the reservoir after polymer flooding,Daqing Exploration and Development Research Institute independently developed the deep fluid diversion agent--PPG/ polymer system.Deep profile control technology is used to drive oil.PPG/ polymer flooding,as a fourth oil recovery technology with great potential after polymer flooding,is a system of high concentration polymer carrying PPG,which forms a combination of solid and liquid.It not only retains the characteristics of particles but also has the effect of viscosification,which can migrate to the depth of oil layer and play a role of deep profile control,thus solving the practical problems of low efficiency and ineffective circulation.In this paper,the stability,plugging and viscoelasticity of PPG/ polymer system were evaluated by laboratory experiments.For PPG with different expansion times and different particle sizes,a long sand-filled tube model with pressure measuring points was used to study the PPG migration law.Combined with the three-pipe parallel experiment,the compatibility of PPG with oil reservoirs with different permeability was studied to optimize the PPG system.The cumulative absorption ratio of each permeable layer was analyzed and the oil displacement mechanism of PPG/ polymer system was studied.The optimal concentration of PPG and polymer and the optimal injection amount of protective slug were optimized by three-pipe parallel experiment.A large three-dimensional heterogeneous physical model combined with the five-point well pattern model was used to simulate the actual field for laboratory experiments,and the pressure field analysis and saturation monitoring were compared to further study the seepage law of PPG/ polymer system.Experimental results show that: Under the condition of fixed expansion ratio and compressive strength of PPG,the resistance coefficient and residual resistance coefficient caused by PPG/ polymer system in core increase with the increase of PPG size.Under the condition of fixed particle size,the larger the expansion ratio of PPG,the smaller the resistance coefficient and residual resistance coefficient caused by PPG/ polymer system in the core.The PPG/ polymer system with particle size of 0.15?0.3mm,expansion ratio of 3 and compressive strength of 1.7MPa was optimized according to the ratio of liquid absorption,fractional flow rate and recovery percent of reserves of each layer.The optimal injection parameters for PPG/polymer flooding were 1200mg/L polymer,400mg/L PPG,and 0.2PV iso-viscosity protective slug,resulting in an enhanced recovery of 15.21%,the final recovery degree is 66.68%.In a large three-dimensional heterogeneous physical model,the pressure decreases gradually from injection well to production well,and there is an obvious gradient distribution.PPG passes through the pore throat in the way of "accumulation blocking-pressure increasing-deformation migration",making the injection pressure increase in a zigzag pattern,thus achieving dynamic control and flooding,greatly reducing the average oil saturation in the middle and low permeability zones,and significantly improving the recovery degree.Well pattern infill variable streamline PPG/ polymer flooding is 16.1% higher than polymer flooding,and 2.59 percentage points higher than one-injection-one-production.The understanding obtained in this paper provides a theoretical basis for field practical application and has guiding significance for field practical application.