Study Of The Method To Enhance Oil Recovery After Polymer Flooding In Offshore Heavy Oilfields

With the continuous exploration of oil resources in China,crude oil reserves are declining.Heavy oil resources are becoming more and more important hydrocarbon energy.How to make full use of heavy oil resources fast and efficient are the important issues currently faced.Due to limited life of the platform and facilities,offshore heavy oil development process has timeliness,for the EOR technology should highlight the word of"early" especially for the areas rich in heavy oil resources must adopt high-speed and high-efficient development.Currently,Suizhong 36-1 oilfield which has been in high water cut in Bohai will be the end of polymer flooding.The paper focus that offshore oilfield has few monitoring data of residual oil and has difficulties on the fine description of remaining oil.Based on the field geological characteristics of typical well group,3D heterogeneous electrode model is designed and made to simulate the actual well groups.Based on the mining history,model flooding scheme is established to monitoring the change of residual oil field after water flooding and polymer flooding.Combined with the residual oil prediction results of numerical simulation of actual well groups,a comprehensive analysis of displacement rule with offshore heavy oil polymer flooding is made.In the plane,the polymer flow to the residual oil area from the mainstream line to non mainstream line of both sides,thus displacing residual oil and improving vertical sweep range.Combination of numerical simulation and 3D heterogeneous electrode model enrich the description method of macro remaining oil distribution of heavy oil in offshore,which provide foundation for further EOR on offshore oilfield with polymer flooding.By using lithography glass model,a study on the distribution law of macro remaining oil in heavy oil and light oil with polymer flooding is made.Whether heavy or light oil,polymer flooding can effectively enlarge the swept volume,heavy oil with polymer flooding dose not effect as good as light oil dose;heavy oil after polymer flooding,oil film is thick,residual oil in porosity contains more,cleaning efficiency is poor and unswept region is larger.Considering the actual production in offshore oil field,this paper studies technology of the chemical flooding after polymer flooding to enhance oil recovery mainly contains high concentration polymer flooding,binary compound flooding and alternative injection of natural gas and polymer.During the study of S/P binary system flooding numerical simulation after polymer flooding in Suizhong 36-1 oil field,viscosity?interfacial tension?adsorption quantity and phase permeability curve of S/P binary system,are simulated mainly based on static experiment and determined by the method of expert experience or experience from other blocks.Through indoor physical oil displacement experiment,the law of physical and chemical parameters variation is studied.By the method of viscosity,the relative permeability curve of heavy oil binary compound system is determined in offshore and the experimental results are applied to numerical simulation of binary compound flooding.For offshore heavy oil,through variation law of parameters of interfacial tension and viscosity with the increase of injection PV number at different position of core with different lengths,the change of viscosity and interfacial tension of binary compound system through the formation shear and adsorption after injection is simulated.After stabilization,interfacial tension is 5-10 times after the injection and the viscosity parameter retention rate is about 57%.After binary compound system getting through the 90cm core and viscosity at delivery end become stable,the distribution law of viscosity in rock is obtained.Fitting curve of system viscosity at different position is established based on which the effective viscosity of displacing process is calculated.A new processing method of phase permeability viscosity of binary compound system is put forward and applied into determination of phase permeability curve of binary compound system at different capillary numbers in offshore heavy oil.According to the target I of Suizhong 36-1 oilfield,based on the indoor experiment result,on the basis of numerical simulation scheme optimization of enhanced oil recovery method of binary compound flooding,alternative injection of gas and polymer and high concentration of polymer flooding after polymer flooding,the potential of enhanced oil recovery is studied,which compared with the result of three-dimensional heterogeneous electrode model,show that in the same injection rate conditions of the high concentration of polymer flooding and binary compound flooding after polymer flooding,both can expand the swept volume.Swept volume coefficients of the high concentration of polymer flooding and binary compound flooding respectively is 82.58%,80.65%.Because high concentration polymer has high viscosity,it expands more vertical and plane sweep areas effectively.But the binary compound system has a great effect on improving the oil displacement efficiency,which can increase 8.22%compared with high concentration of polymer flooding.Therefore,for offshore heavy oil field,on the selection of binary compound system,in the conditions of the actual situation permit,the viscosity of the system should be increased as much as possible.Compared the enhanced oil recovery potential of well group,the high concentration of polymer flooding,binary compound flooding and alternative injection of gas and polymer has different degree on EOR and improve well group recovery rate respectively 4.33%,7.17%and 5.83%.Binary compound flooding after polymer flooding is helpful to the target block with high speed and efficient development.