Mechanistic Research Of Weak Gels Displace Oil And Divert Fluid By NMR Technique

In the face of low oil recovery in the high-water production period,the injection of weak gels was an effective method widely used.Weak gel was a kind of weaker polymer cross-linked gel,which had better rheology than general gel used for profile control,and can penetrated deeper into the layer.It had a larger viscosity than polymer solution.After gelation,it can block the high-permeability layer.At present,the research on the mechanisms of weak gels displace oil and turn fluid was mainly to use the glass sand filling model.Although the fluid distribution in the core can be visualized,the model may be different with reality greatly.In this paper,the NMR technique combined with the single-tube core model was used to test the displacement characteristics of the optimized weak gel in homogeneous and heterogeneous cores by the oil distribution in cores.Analyzing and processing the data of T₂ spectrums and nuclear magnetic images in the displacement processes,the mechanisms were as follow:?1?When weak gel was injected,it can affect both large and small porosity of the core;The larger coefficient of variation of permeability,the stronger ability to use large pores.The enhanced oil recovery of large pore size was-2.8%?5.6%higher than that of small pore size.It mainly seepaged into the high permeability layer,and the oil recovery of the high permeability layer was negatively correlated with the average water permeability of the core.However,the weak gel had a greater influence on the low-permeability layer.The enhanced recovery rate of the low-permeability layer was8.1%?12.4%higher than that of the high-permeability layer.The greater permeability difference,the lower oil recovery rate of the low-permeability layer.?2?After the weak gel was gelatinized,the permeability of the heterogeneous core can be adjusted,and the subsequent water flooding was turned to the low permeability layer.The enhanced oil recovery rate of the low permeability layer was 4.5%?11.4%larger than that of the high permeability layer.And the greater difference in permeability,the higher enhanced oil recovery of the low permeability layer.Most of the subsequent water flooding used large-pore residual oil.The smaller permeability difference,the stronger ability to use large pore size.The large pore oil recovery was higher than the small pore oil recovery about-5%?6%.Increasing the oil recovery capacity of the low permeability layer was positively correlated with the permeability difference.?3?The enhanced oil recovery in the weak gel injection stage was about 1.8 to 2.8times higher than the subsequent water flooding stage.And the oil displacement effect was greater than the adjustment profile.?4?Weak gels were most suitable for heterogeneous cores with low average water permeability and high permeability difference.?5?The remaining oil after secondary water flooding in the low permeability layer was about 6%?14%more than oil in the high permeability layer,and oil in the large pore size was about 16%?22%more than oil in the small pore size.In the future,it was necessary to increase the exploitation capacity of the large-diameter residual oil in the low-permeability layer.