Research On The Preparation And Displacement Mechanism Of Soft Heterogeneous Compound Flooding System

Moderatehightemperature?80^oC¹10^oC?andmoderatehighsalinity?1.0×10⁴mg/L¹.0×10⁵mg/L??MHTHS?reservoirs feature many critical reservoir conditions,such as high temperature,high salinity,and formation heterogeneity.Due to poor temperature and salinity resistance of polymer,poor salinity resistant of alkali,channeling and high injection pressure during gas flooding,traditional EOR methods could not meet the urgent requirement of enhanced oil recovery in the MHTHS reservoirs.According to these technical difficulties,based on a self-developed system of phenolic resin dispersed particle gel?DPG?and high efficient surfactant with temperature and salinity resistant,a novel temperature and salinity resistant soft heterogeneous compound flooding system featuring will be prepareted for the MHTHS reservoirs.DPG particles have been successfully prepared using bulk gel through a simple high mechanical shearing method.According to the viscosity changes,the whole preparation process can be divided into two major stages:the bulk gel cross-linking reaction period and the DPG particle preparation period.The DPG particles with nanometer to micron size?750⁵000nm?were prepareted,and it has the characteristics of regular shape,low viscosity,negatively charged,high shearing resistance and aging aggregation capacity.According to the size distribution,a mathematical model of prepation of DPG particles was set up.Based on the experimental results and DPG particles prepared dispersion device,a mathematical model was set up to describe the relationship between shearing rate,shearing time and shearing space.Using this model,software was developed for industrial production.The large-scale production can be easily conducted through adjusting the preparation parameters.It helps the theoretical research turn to field production.The soft heterogeneous compound flooding system was prepared through the screen criteria of formation compatibility,viscosity,and interfacial tension?IFT?.The sytem exhibites better abilities of lowering IFT to 10^-3 mN/m,and has low viscosity,negatively charged,low thermal stability,high shearing resistance,aging aggregation and wettability reversal capacity.The core flowing expriments show that the soft heterogeneous compound flooding system can effectively enter in-depth formation,and improve micro profile control,then improve the swept volume and oil displacement efficiency,and enhance oil recovery.The interaction mechanism of soft heterogeneous compound flooding system was elaborated.The adsorption behavior of surfactant on DPG particles is typical of the Langmuir adsorption.Wherears,the adsorption behavior in the interfacial layer is competitive adsorption among surfactant,DPG particles and DPG particles with adsorbed surfactant.Through diffusion,preferentially adsorbed,macromolecules rearrangement and aggregation behavior,a viscous elastic adsorption layer was formed in the interfacial layer.The adsorption behavior increases the interfacial tension reduc tion capacity of soft heterogeneous compound flooding system,and makes the DPG particles have oil displacement capacity.The interaction force between heterogeneous compound flooding systems and different wettability of reservoir surfaces,and soft heterogeneous compound flooding systems are repulsive force.The added surfactant improved the negative charge of soft heterogeneous compound flooding system which enhanced repulsive force.The steric effect and electrostatic interaction are the driving factors of repulsive force.The repulsive force prompts the soft heterogeneous compound flooding system into the in-depth formation.The adsorption and retention of soft heterogeneous compound flooding system in the sock surface improve the micro profile control.The oil displacment mechanism of soft heterogeneous compound flooding system was elaborated.The weak chromatographic separation effect was generated when the soft heterogeneous compound flooding system flows in porous media.However,it has a slight influence on the displacement effect.The soft heterogeneous compound flooding system can directly pass or by deformation through porous media and enter deep formations.By directly plugging,bridging,adsorption and retention,the system can effectively reduce the permeability of porous media in high permeability zones and improve micro profile control.The increased viscosity of DPG particles can improve the flowing ratio of surfactant and reduces its diffusion rate.It can effectively reduce the permeability of porous medium in high permeability zone and divert fluid into the low permeability zone,thus improve micro profile and enhance oil recovery.Additionally,the surfactant in the system can adsorbs on the DPG particle surface which improves deep migration capability and oil displacement capacity of the soft heterogeneous compound flooding system.The synergistic effect of the two components of the soft heterogeneous compound flooding system improve the swept volume and oil displacement efficiency,and then enhance oil recovery.