Abstract:A low permeability reservoir features fine throat and complex porous structure, which an artificial micro pore model can not well represent. A water flooding experiment was carried out with the real core and simulated oil without hydrogen. The water-oil two-phase fluid flow was studied using the technique of nuclear magnetic resonance, to obtain the distribution of irreducible water, irreducible oil and produced oil in cores of different porosity during drainage and imbibition, and to reveal the formation mechanism and imbibition mechanism quantitatively during the water displacement. The results show that the bigger the pore radius is, the lower the irreducible water saturation will be; the main reservoir space of low permeability reservoir is a medium with pores of more than 0.1 μm in radius; residual oil is mainly distributed in mid-small pores; and imbibition is significant in low permeability reservoir.