Study On The Performance Change Of Long-distance Transport Of Weak Base Asp Flooding In Class Ⅲ Oil Reservoirs

At present,Class I and Class II oil reservoirs have been largely developed in Daqing Oilfield.In order to maintain oil production,the development of Class III oil reservoirs become imminent in Daqing Oilfield.The strong base ASP flooding has been widely used in Class I and Class II oil reservoirs in Daqing Oilfield and has achieved good effect of oil production.Components in the ASP system have a synergistic effect,which can produce ultra-low interfacial tension and improve mobility ratio.However,the alkali would produce many negative effects,such as the dissolution of rock skeleton,formation scaling,and emulsification of production fluid,which will increase the difficulty of exploitation.Class III oil reservoirs in Daqing Oilfield have the characteristics of low permeability,small effective thickness and strong heterogeneity.Due to the adaptability of the strong base ASP system is poor,it is necessary to adopt more suitable enhanced oil recovery technology for development.Compared with the strong base ASP system,the weak base ASP system has less damage to the reservoir.Therefore,this paper studies the performance change of long-distance transport of weak base ASP system in Class III oil reservoirs through indoor static evaluation and dynamic oil displacement experiment.Firstly,the evaluation of viscosity,shear,temperature resistance and emulsification effect of two ASP systems was conducted,and the adaptability of injection viscosity and injection speed was studied by using displacement experiments.Subsequently,the oil displacement effect,the pressure along the tube and the distribution of residual oil in the weak base ASP system under long-distance migration conditions were studied through the 30 m long tube sand filling model flooding experiment.Finally,the change rule in the process of transportation about polymer concentration,alkali concentration,surfactant concentration,viscosity,interfacial tension and emulsification effect of each sample point of 30 m long tube were studied.The results showed that compared with common polymer ASP system(P-partial hydrolysis HPAM,S-petroleum sulfonate and A-sodium carbonate),the salt resistance of polymer of low molecular weight and salt resistant ASP system(P-low-molecular-weight salt-tolerant polymer,S-petroleum sulfonate,and A-sodium carbonate)was stronger,the viscosity was greatly affected by the shear rate,the change rule was basically the same,and the emulsification effect was equivalent.The relationship between injection speed and pressure and the relationship between viscosity and pressure accord with traditional Darcy’s law.During long-distance migration of Class III oil reservoirs,the long-distance migration rule of components of the two ASP systems were similar in the model.The ultra-low interfacial tension could only be maintained to 8.9 m of the model.The viscosity of polymer of low molecular weight and salt resistant ASP system at the distal end of the model was higher than that of common ASP system,and polymer of low molecular weight and salt resistant ASP system has a better start-up effect on remaining oil.Both ASP systems produced emulsification at 638 cm and demulsified at 2163 cm.The polymer of low molecular weight and salt resistant ASP system has a better oil displacement effect,and the oil recovery was 17.04%,while the oil recovery of common ASP system was only 13.48%.