| China's oil reservoirs are rich in heavy oil resources.In order to efficiently and rationally use heavy oil resources,most of them use water-driven reservoirs.After the development of water flooding,the polymer can improve oil recovery to some extent,but when the viscosity of heavy oil is increased,in order to better develop the reservoir,the viscosity of the polymer required will increase,which will cause the injection pressure to be too high,and on the other hand,the phenomenon of profile reversal will result in poor polymer flooding results.In order to improve the development effect of heavy oil reservoirs,it is necessary to analyze the two root causes of oil recovery:the contribution rate of sweeping efficiency and washing efficiency to the recovery of heavy oil reservoirs,and analysis of the recovery of high-viscosity oil.The role,combined with the on-site crude oil viscosity range,provides guidance for improving heavy oil recovery.Firstly,combined with the heterogeneity of the Bohai heavy oil reservoir,the heterogeneous model core is used.The polymer is selected after shearing,the concentration is 1500mg/L(125mPa·s),and the viscosity of the crude oil is 305mPa·s.The experiment was carried out to study the sweeping law in the process of polymer flooding.The main permeation layer of polymer flooding to enhance the recovery factor by enlarging the sweep efficiency was MATLAB software.In order to quantify the contribution of sweep efficiency to recovery factor,microscopic three-layer heterogeneous visualization slides were used for analysis,first water flooding,then polymer flooding,pixel recovery calculation,water flooding 10%,poly drive 55%,use the area method to calculate the sweep efficiency,water flooding 27%,polymer flooding 90%,comparative analysis of the sweep efficiency and recovery factor before and after polymer flooding,and then calculate the contribution rate of the sweep efficiency to the recovery rate of 71%,At the same time,the viscosity of the polymer was changed to conduct research.Therefore,the contribution rate of the sweep efficiency to the recovery factor is limited,and the viscosity is increased subsequently,and the contribution of the sweep efficiency to the recovery factor is reduced.In order to further improve the recovery rate,the washing efficiency in the affected area should be improved.The microscopic visualization study was also used.The experiment selected the 1500mg/L polymer+0.1%surfactant in the binary system.The formula was used to calculate the oil washing efficiency,and the oil washing efficiency of the system was increased by 6%.The binary composite flooding was harvested.The rate is 60%,the contrast polymerization drive increases by 5%,the contribution rate of oil washing efficiency to oil recovery is 80%,and then the contribution rate of oil washing efficiency to oil recovery under different interfacial tensions is studied.When the interfacial tension reaches 10-3mN/m After that,the increase in recovery rate gradually stabilized.Comparing the contribution of sweeping efficiency and washing efficiency to oil recovery can be found:to improve the recovery rate of heavy oil reservoirs,when the sweep efficiency is applied to a certain extent,the subsequent enhanced oil recovery should be based on improving oil washing efficiency.In order to verify this point,two heavy oils with different viscosities were selected for verification,and the viscosities were 750mPa·s and 1050mPa·s,respectively.The microscopic visualization experiment method was also used to study the contribution of the sweep efficiency and the washing efficiency of the two crude oils to the recovery factor.The results show that as the viscosity of crude oil increases,the contribution of sweeping efficiency to oil recovery shows a gradual decline,while the contribution of washing efficiency to oil recovery shows a gradual increase.Therefore,for heavy oil reservoirs,as the viscosity of the crude oil is higher,it is preferred that the type of the displacement agent should be based on improving the oil washing efficiency,and the sweep efficiency is supplemented. |
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