Study On Plugging Control Performance And Oil Displacement Effect Of A Low-Initial-Viscosity Gel System

With the continuous increase of oilfield development,the contradiction of reservoir heterogeneity is becoming increasingly prominent,resulting in the formation of dominant seepage channels.With the continuous improvement of water content in the produced liquid,crude oil cannot be effectively extracted.Gel plugging technology is an effective method to solve this problem.However,conventional gels experience problems such as high initial viscosity and they easily contaminate the medium-and low-permeability layers.It is no longer applicable to reservoirs with strong heterogeneity.Therefore,a low-initial-viscosity gel plugging agent is proposed in this paper.By optimizing the concentration of polymer,crosslinking agent and other functional additives,the optimal plugging agent formula with low initial viscosity,long low viscosity period and strong gelation viscosity was obtained.In order to test the application range of low-initial-viscosity gel plugging agent to reservoir environment,salt resistance test,shear stress test and the influence of PH value on gelling performance were carried out,and the plugging performance evaluation test was carried out by cores with different permeability.Finally,the three-tube core physical model is used to simulate the actual formation displacement experiment.The adjustment ability of low-initial-viscosity gel plugging system to interlayer contradiction and its influence on oil displacement effect were investigated.The best injection volume and timing of gel plugging agent and the best slug combination injection mode of water plugging,profile control and oil displacement are selected.The research results showed that the best formulation of gel plugging agent is as follows:500-1000 mg/L polymer,1000-2500 mg/L cross-linking agent,200-500 mg/L regulator,100-150 mg/L retarder,and 100-200 mg/L strengthening agent;its initial viscosity is less than 10 m Pa·s,the gelation time is controllable within 10 to 60 days,and the gelation viscosity is above 2000 m Pa·s.The gel system has good salt resistance and shear resistance,with a p H range of 8?9.The gel system has good core plugging performance,and the plugging rate of water from 0.5 to 4.0?m~2is more than 99%.The results of oil displacement experiments showed that the low-initial-viscosity gel plugging agent with suitable injection volume can not only effectively seal the high-permeability layer and improve the heterogeneity of the oil layer,but also basically does not pollute the middle and low-permeability layers.For secondary polymer flooding reservoirs,the optimal injection amount of gel plugging agent is 0.1PV.The earlier the gel plugging agent is injected,the better the plugging effect is.The best slug combination injection mode for the combination of water plugging,profile control and oil displacement is 0.07PV gel slug+0.2PV polymer slug+0.03PV gel slug+0.5PV polymer slug.Under this injection mode,the final recovery can be increased by 17.04%compared with that after the end of polymer flooding.