Research On Numerical Simulation Of Molecular Viscoelastic Effect In Polymer Flooding

Polymer flooding has become one of the necessary methods to improve oil recovery in old oil fields,but the flow mechanism of polymer flooding is difficult to be clear.The recovery rate of waterflooding is generally not high,and there is still a large amount of remaining oil in the formation.Therefore,the research on the mechanism of polymer flooding after waterflooding is of great significance for enhancing the oil recovery by polymer flooding.Although the predecessors' microand macro-experimental studies on polymer flooding technology,mostly in the macro experimental stage,have achieved certain results,most of them are based on certain assumptions and ideal conditions,so it is difficult to make quantitative and in-depth analysis.The theory of microscopic displacement is lacking,therefore,based on molecular simulation technology,the polymer materials and polymer flooding process were visualized,and the properties of polymer solution and the polymer flooding process mechanism were analyzed at the atomic level.Different from the traditional experiments,this paper employed molecular simulation technology performs modeling and simulation on a computer from a micro level-computer experiments.As a new research method to explore the mechanism,it has a high degree of flexibility,can meet the extreme conditions of complex formations,offset the excessive simplification of experiments and theory,and conduct research close to the actual reservoir conditions.Molecular simulation has powerful capabilities in studying the properties of reservoir rocks and fluids,their interactions,and related phenomena at the atomic level.In the molecular dynamics simulation,the properties of the study can be extracted from the time evolution analysis of the positions and velocities of atoms by numerically solving Newton's equations for the motion of all atoms in the system.It is applied to polymer flooding in oilfields,and the molecular configuration of polymer flooding agent and oil-displacement mechanism are discussed respectively.Firstly,two polymer displacement agents(NPAM and HPAM)were designed and analyzed,and molecular modeling of polymer solution was carried out to explore its rheological and viscoelastic mechanisms;and the microscopic mechanism of polymer displacement agent is analyzed by simulating it under reservoir condition.Secondly,polymer flooding is modeled to simulate the displacement process,and the microscopic mechanism is observed by visual means.The microscopic study of polymer solution shows that the viscoelastic properties of HPAM are better than that of NPAM,and the former adsorption effect in the formation is weaker than that of the latter.And through the process simulation of water flooding model and polymer flooding model,it is obtained that the oil washing efficiency of polymer flooding is higher than that of water flooding.Furthermore,through analysis,the viscoelasticity of the polymer solution is the main mechanism for the polymer to drive the crude oil out.Computer molecular simulation reveals the seepage mechanism of polymer flooding from the microscopic scale,and enriches the flow theory system of polymer flooding.The results achieved will provide useful guidelines,which considerably help to conduct better design and optimal operation of production plants,and improves the recovery rate of polymer flooding.