Study on parameters limits of polymer profile control displacement in medium and low permeability reservoirs based on nuclear magnetic resonance

The high permeability contrast, variation coefficient and heterogeneity of sandstone reservoirs in L oilfield cause large amount of oil remaining in medium and low permeability reservoirs after water flooding development. It is difficult to improve the development effect by conventional water flooding, thus profile control displacement is required to eliminate interlayer contradiction, enhance displacement efficiency and sweep volume, and improve the impact of water flooding on reservoir development. Based on nuclear magnetic resonance(NMR) technique, polymer profile control displacement experiments are carried out in medium and low permeability sandstone cores and T2 spectrum curves before and after polymer injection are converted into distribution curves characterizing pore throat radius to analyze the laws of polymer flooding with different molecular weight and concentration, quantitatively evaluate the displacement effect, analyze oil producing in pores and the radius of producible pore throat of reservoir in the process of profile control displacement, and evaluate polymer injection performance. The lower permeability limit of profile control displacement is 30×10 −3 μm 2 , polymer molecular weight is 8 million and concentration is 500 ppm. Polymer molecular weight and polymer concentration can be appropriately increased for reservoirs with permeability of > 70 ×10 −3 μm 2 . Fine geological modeling and numerical simulation are performed for typical well blocks in L oilfield, determining the minimum net pay thickness is 3 m, well spacing of 200 m and optimum well pattern of five-spot pattern. The research provides technical support for injection-production parameters optimization and profile control displacement optimization of A injection scheme design.