Effect Of Combination Of Polymer Concentration On The Performance Of ASP Flooding

ASP flooding is an effective EOR?Enhanced Oil Recovery?method in China,which can increase oil recovery by about 20%on the basis of water flooding.The change of the injection mode of the ASP system has a great influence on ASP flooding efficiency.Therefore,it is of theoretical significance to study the injection mode of ASP flooding.ASP flooding presents great application potential in class ii reservoirs in Daqing Oilfield.However,compared to the main-layer reservoirs,the class ii layer reservoirs exhibit some drawbacks including low permeability,thin oil layer,serious heterogeneity,uneven distribution of the remaining oil,and the difficulty of exploring and development.In addition,there do exist some problems in the application of the conventional ASP flooding in class ii layer reservoirs.For example,the sweep efficiency is relatively lower in the formation with serious heterogeneity,and the amount of the injected chemical agent is too much.Therefore,the injection mode of the ASP flooding in class ii layer reservoirs in Daqing Oilfield should be optimized.In view of the technical limitations of the application of conventional ASP flooding in class ii layer heterogeneous reservoirs in Daqing Oilfield,this study first evaluates the matching of different permeability cores in class ii layer reservoirs with the target ASP system.On the basis of the screening results,different types of ASP flooding with different polymer concentration combinations are carried out by using interlayer and the interlayer heterogeneous cores.In order to further explore the effect of ASP flooding injection mode on the areal and vertical sweep efficiency,the three-layer heterogeneous physical model with five-spot well spacing pattern is designed and fabricated,and then is used to analyze the ASP flooding production performance,the fluid flow characteristics,the effluent property change,and the distribution of pressure and oil saturation in the model.The mechanisms of varying viscosity ASP flooding for EOR are described in details.Experimental results show that the ASP system with target polymer concentration has a good matching relationship with the cores with the permeability of 300-800×10^-3?m².In the heterogeneous core models,the lower viscosity ASP slug in descending viscosity ASP flooding can penetrate into the middle and low permeability layers more efficiently,which presents the better effect of secondary water flooding in the middle and low permeability layers.In the three-layer heterogeneous models with five-spot well spacing pattern,compared to the conventional ASP flooding and ascending viscosity ASP flooding,with the same amount of chemical agent injected,the decending viscosity ASP flooding presents a higher oil recovery.On one hand,the higher viscosity of the first slug of descending viscosity ASP flooding results in a better mobility control effect,which tunes more of ASP system and subsequently injected water to flood middle and low permeability layers and makes the overall effect of descending viscosity ASP flooding better.On the other hand,the higher viscosity of the first slug of descending viscosity ASP flooding has a protective effect on the system component,i.e.,the high viscosity slug can effectively reduce the adsorption and dilution of the surfactant and alkali from formation water.Therefore,the synergistic effect of the ASP flooding can be better presented,and the oil displacement efficiency can be further improved.