Producing limit of CO2 flooding throat based on nuclear magnetic resonance
According to the basic principle of NMR,the relation between NMR T2 relaxation time and pore throat radius was deduced through pore simplification.NMR T2 map was converted into core pore throat ra-dius distribution by using numerical difference and least square method combined with high-pressure mer-cury injection core pore throat distribution.On this basis,the change of oil saturation and the synchronous change of signal amplitude in the process of core flooding are used to analyze the change curve of signal am-plitude of different pore-throat radius of water flooding and CO2 flooding,and the minimum orifice throat production limit under different development modes is determined.The shows that the ultra-low permeabil-ity block of Chaoyanggou Oilfield is hydrophile,the recovery degree for low and high pressure water drive is 28.0％and 30.0％respectively,48％and 64％for immiscible and miscible gas drive respectively.In wa-ter flooding,movable oil is mainly used in pores with pore throat radius greater than 1 μm.In immiscible flooding,the maximum pore throat radius is 0.15 μm.Miscible flooding does not improve the throat limit,but the displacement efficiency is greatly improved.The light components in crude oil are displaced by CO2,the viscosity of residual oil increases,and the immovable fluid increases by 1/3～3/4 on the original basis,and the NMR spectrum shifts to the left.The conclusion provides a good reference for development plan of CO2 flooding.
CO2 floodingnuclear magnetic resonancehigh pressure mercury injectionthroat radiuspro-ducing limit
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