Study On Low Salinity Waterflooding Numerical Simulation Of Ultra-low Permeability Reservoir

The current waterflooding development is still the most important production method in the oilfield exploitation process,while the low salinity waterflooding refers to the injection of water containing low concentrations of soluble solids in the reservoir.The main mechanisms for enhanced oil recovery are fines migration and alkali-like flooding,multiple ion exchange with the cations in the clay stuctures,causing wettability alteration,etc.,but the main mechanism is not specific.The B-425 reservoir is a low-permeability reservoir in Shengli Oilfield.In-field experiments with low salinity waterflooding were conducted among some injection and production wells groups.The effect is obvious,but the mechanism of enhanced oil recovery is not yet clear.To solve this problem,in this paper,a combination of laboratory experiments and numerical simulations was used.Nine groups of core flooding experiments were carried out.Three kinds of flooding methods,high-medium-low salinity continuous flooding,middle salinity flooding and low salinity flooding,were used to conduct experiments.The effects of injection methods,salinity,and permeability on the recovery of low-salinity waterflooding were studied,and the characteristics of the relative permeability curves,the displacement pressure and the change of ions and pH in the produced water were analyzed.It was determined that the wettability changes,ion exchange,and particle migration were the main mechanisms for enhanced oil recovery.A numerical simulation model of water flooding with low salinity was established,and the experimental results were verified by adjusting the salinity and the curve of the relative curves.Based on this,the development of numerical simulation is further carried out to compare and analyze the changes in the permeability curves,the influence of the injected water salinity on the recovery,and to supplement the model workload.Finally,the actual well group verification was performed in combination with the influencing factors.The experimental results show that the low salinity waterflooding is significantly improved by nearly 10~20% compared to conventional waterflooding recovery;Among them,the continuous flooding method has the highest displacement efficiency in the long term,while the medium and low salinity displacement methods have a significant effect on the recovery in the short term;for existing cores,the lower the permeability,the lower the degree of mineralization waterflood.The better the effect,the migration of particles was found based on theoretical analysis of displacement pressure difference and experimental process monitoring.The number-model expansion study has found that the rock is more oil wet,the low salinity water flooding compared with the ordinary water flooding,the greater the increase in the rate of recovery,the effect is more obvious;2000 ~ 5000 ppm can be used as a rational mineralization limit.