Numerical Simulation Of Migration Of Polyacrylamide In Soil For Tertiary Oil Recovery

As an important petrochemical city in the country,Daqing City shoulders the destiny of the country and contributes valuable material wealth to China’s modernization.Daqing Oilfield has entered the stage of high water cut later development,so the industrial use of ternary composite（ASP）floodingto improve oil recovery.If the polyacrylamide（PAM）in the ASP flooding leaks during the process of transportation,transportation or injection,it will cause serious pollution to the soil in Daqing City.In addition,PAM has a wide range of applications in agriculture.Excessive PAM leaks into the soil,causing adverse effects such as soil compaction.However,there are few reports on the impact of PAM on soil in Daqing.Therefore,establishing a PAM migration model and summarizing the migration law of PAM has far-reaching significance for its prevention and pollution caused by PAM.In this paper,the adsorption characteristics of PAM in chernozem and saline soilare determined by static adsorption experiment.The isothermal adsorption curves and isothermal adsorption equations show that PAM perform Langmuir adsorption in both kinds of soil,and the adsorption capacity of PAM in chernozem is greater than that in saline soil.The main reason for this phenomenon is that compared with saline soil,the content of montmorillonite in chernozem is higher and the content of organic matter is lower.Experimental results show that PAM has the highest adsorption capacity at 40°C.The effect of pore velocity on the migration of PAM in soil is investigated by dynamic migration experiment.The experimental result shows that as the flow rate Q increases,the volume required for PAM to reach equilibrium concentration decreases.The dynamic migration experiment uses KBr as tracer.According to the BTCs（concentration breakthrough curve）of Br^-in chernozem and saline soil,the kinetic parameters in the CDE model are estimated.The longitudinal dispersion of chernozem is 0.0045m,and the longitudinal dispersion of saline soil is 0.0071m.These data provide an important basis for predicting the migration and transformation of pollutants in important types of soil in Daqing City.The literature shows that the T-S model can describe the migration process of PAM more accurately because of PAM is a kind of highly entangled macromolecular compound.The isothermal adsorption equation of PAM is coupled with the T-S equation to obtain the migration model of PAM.The comparison between experimental results and simulation results shows that the model has able to predict the migration process of PAM in soilaccurately.The kinetic parameters in the T-S model were estimated based on the BTCs of PAM in two kinds of soil.The estimation results show that PAM behave non-equilibrium adsorption in important types of soil in Daqing.The pore velocity v is an important factoraffecting the migration of PAM in soil.As the pore velocity v increases,the mass transfer coefficient?increases.As the result,the volume required for PAM to reach equilibrium decreases.This conclusion is consistent with the experimental result.Furthermore,the relationship between the pore transport rate v and the mass transfer coefficient?is discussed.The results show that there is a good linear relationship between the pore velocity v and the mass transfer coefficient?of PAM migration in chernozem and saline soil:?（28）131.9v（10）14.38,R²=0.954;?（28）70.87v（10）8.43,R²=0.945.In the case of the same flow rate,the required volume of PAM to reach equilibrium concentration in chernozem is significantly smaller than that in saline soil.This is due to the higher content of organic matter in the saline soil,resulting in a higher content of large-sized aggregates.Therefore,the adsorption capacity of saline soil is poor.The migration model of PAM is used to predict the migration depth of PAM in different time periods.The experimental results show that the migration speed of PAM in chernozem is14.58×10^-3cm/h and the mass transfer coefficient is 16.37 mg/（L·min）when the migration speed is stable under natural conditions,the adsorption is an important factor affecting the migration of PAM in chernozem.When the PAM leaks into the soil,most of the PAM will remain in the upper soil,and only a small part will continue to migrate downward.Therefore,measures should be taken to deal with the contaminated area in time,which can effectively prevent the expansion of the pollution range.