Study On The Method Of Profile Control And Oil Displacement After Water Flooding In Ultra-low Permeability Reservoir

The water injection development in ultra-low permeability reservoirs has the problems of rapid increase in water content,serious water channeling,and low oil recovery.It is urgent to effectively control water channeling in high-permeability channels and to effectively replace crude oil in low-permeability matrices.In response to this urgent need,a technology study on enhanced oil recovery in ultra-low permeability reservoirs that incorporates deep profile control and flooding has been conducted.Developed a"Crude oil saturation plant of tight heterogeneous reservoir model"and broke through the bottleneck technology that affected the accuracy of the heterogeneous reservoir model displacement experiments in ultra-low permeability/tight reservoirs.Based on this,a physical model with water flooding simulation experiment in low permeability reservoir was developed.The results of homogeneous core water flooding experiments show that the main reason for low water flooding efficiency is low microscopic sweep efficiency,and the main type of residual oil after water flooding is microscopic heterogeneous residual oil.The macroscopic sweep efficiency of water flooding is approximated by the PV number at the front edge of water flooding in the heterogeneous model flooding experiment,and the experimental law of water flooding efficiency decreases with increasing permeability difference in the ultra-low permeability heterogeneity model.The residual oil after waterflooding in ultra-low permeability heterogeneous?fractured?reservoirs is the main potential target for enhanced oil recovery.Comprehensive analysis of one-dimensional column core and non-homogeneous?fractured?core flooding experimental results,and cleard the technical direction of enhanced oil recovery in ultra-low permeability reservoirs:to improve the macro-spreading efficiency,and taking into account the improvement of oil displacement efficiency.It is preferable that the active agents with ultra-low interfacial tension and strong emulsifying ability be used to carry out flooding experiments,and the experimental rule that the contribution rate of ultra-low interfacial tension and emulsification ability to oil flooding efficiency changes with core permeability is obtained:The contribution rate of the ultra-low interfacial tension to the oil displacement efficiency decreases as the permeability decreases and in the range of 1000×10^-3?m²⁵×10^-3?m²,the contribution rate of emulsifying ability to the oil displacement efficiency increases with the decrease of permeability.It is thus clear that the leading role of active agent flooding in ultra-low permeability reservoirs is oil-water emulsification,and the ultra-low interfacial tension is an auxiliary property.The local oil displacement pressure gradient of the strong emulsifying agent in the ultra-low permeability core is 18.36%higher than that of the water flooding,and the local oil displacement pressure gradient of the ultra-low interfacial tension active agent is 27.39%lower than the water.Therefore,it can be preliminarily confirmed that the emulsified oil-dispersing agent can block the pores of the microscopic water flow channel through emulsification and improve the microscopic sweep efficiency.In the process of strong emulsifying agent flooding,the resistance coefficient of the core injection end is low?<1?,and the rear resistance coefficient increases in the core.This experimental result shows that the strong emulsion flooding agent is used to solve the ultra-low permeability reservoir.There is a unique advantage in the contradiction between inject ability and deep reservoir plugging.Improved DCA microspheres for deep profile control in ultra-low permeability reservoirs.Aiming at the difficulties of DCA microspheres injection in ultra-low permeability reservoirs and the serious jamming of end faces,the technical ideas of underground polymerization into spheres were proposed.Through the introduction of polymerization inhibitors,preferably initiators,controlling and adjusting the polymerization reaction time,the formation of spheres in the oil reservoir was realized,and the deep profile control technology of underground polymeric DCA microspheres suitable for ultra-low permeability reservoirs was developed.The experimental results show that the resistance coefficient and residual resistance coefficient of the underground polymeric DCA microspheres at the core injection end are significantly lower than those of the original DCA microspheres.The residual resistance coefficient in the middle of the core is significantly higher than that of the original DCA microspheres.That is,the underground polymerized DCA microspheres profile control is a deep profile control technology for ultra-low permeability reservoirs that can relieve the contradiction between injectability and deep sealing property.In view of the special contradiction between the treatment of hydrazine in ultra-low permeability reservoirs and the drive of residual oil in the matrix,the deep profile control and flooding technology of DCA microspheres was developed.The simulation results of the profile control and oil displacement simulation of the ultra-low permeability heterogeneous reservoir model show that compared with the surfactant flooding and the deep adjustment of the DCA microspheres alone,the Emulsion Flooding-DCA microspheres deep-tuning composite technology have obvious advantages on improves the recovery rate and decrease the moisture content rate.The subsequent flooding methods in the Emulsion flooding-DCA microspheres deep adjusting composite technology of ultra-low permeability oil reservoir were optimized.Using the enhanced oil recovery as an indicator,a deep-adjustment-displacement composite technology for ultra-low permeability heterogeneous reservoirs combined with emulsion flooding-DCA microsphere-depth-CO₂ flooding was established.The DCA microsphere deep-strength emulsified oil flooding composite technology was used to conduct field tests in a ultra-low permeability reservoir-CQ oil field.The 2 well groups increased oil by 2284 tons and 1225 tons respectively,and the effect of profile control and oil displacement was significant.