Experimental Study On Oil Displacement Efficiency Of Xingliu Block With Extra High Water Cut In Later Stage

Daqing oilfield has been in the late stage of extra-high water cut after a long period of development,and the comprehensive water cut has reached more than 95%.Taking xingliu block of daqing oilfield as the research object,this paper studies the pore structure characteristics of the reservoir in the late period of extra-high water cut.Through conventional oil displacement experiments,the relationship between pore structure and oil displacement efficiency was established,and the development potential of the reservoir in the later stage of extra-high water cut was evaluated.Different oil displacement experiment methods were used to evaluate the change of oil displacement efficiency under different methods and displacement conditions,and the mechanism and measures of improving oil displacement efficiency at the later stage of extra-high water cut were clarified,which provided reference basis for improving oil recovery at the later stage of extra-high water cut.The research results are as follows:(1)In the mercury injection experiment,with the increase of core permeability,the displacement pressure decreases,the pore connectivity becomes better,the proportion of larger radius pore throat increases,and the pore radius increases.The skewness tends to be concentrated and increases,and the distribution symmetry of pore throat becomes better and deviates to the direction of rough skewness.The structural coefficient tends to be concentrated and becomes smaller,and the degree of the flow detour becomes weaker.(2)Late in determining the relationship between pore structure and oil displacement efficiency evaluation,with the increase of the average permeability cores,conventional reservoir of thin and poor reservoirs are irreducible water saturation decreases with the increase of permeability,and the moisture content reached more than 95% of the oil displacement efficiency and ultimate oil displacement efficiency are increased,the pore structure and oil displacement efficiency with strong positive correlation,then the reservoir in determining late stage still has large development potential,for the next step research provides the theoretical support measures to improve oil displacement efficiency.(3)In the high-power and high-speed water flooding experiment,by increasing the PV number,the effect of oil displacement efficiency change is not obvious,but with the increase of injection speed,the oil displacement efficiency increases,the increase range is between 1.46% and 2.45%;In the periodic water injection experiment,the oil displacement efficiency has been improved to a certain extent in each cycle.In the early stage of the cycle water injection,the oil displacement efficiency has a fast increasing trend,but with the increase of the number of cycles,the oil displacement efficiency has a slow growing trend.The increase range of oil displacement efficiency is between 1.72% and 2.35%.In the experiment on the direction of liquid exchange flow,after core forward displacement is carried out,the oil displacement efficiency of core is improved with a range of 1.17%~ 2.64%,but the change trend is relatively slow.