Further Study on the Effect of Interfacial Tension on Cocurrent Spontaneous Imbibition Based on Direct Simulation and NMR

Due to the low permeability and small porosity, tight reservoirs are usually developed by volume fracturing of horizontal wells, and spontaneous imbibition is one of the important mechanisms. Capillary force is the dominant force for spontaneous imbibition in tight reservoirs. This paper presents a detailed study of spontaneous imbibition by a direct simulation method (Lattice Boltzmann method) and core experiments of nuclear magnetic resonance and proposes a method to characterize the degree of oil utilization on the core by using the variation of oil volume at the core cross section. It is found that the higher the interfacial tension, the higher the final recovery rate. The core is divided into four areas (the larger the area number, the farther away from the inlet) along the direction of spontaneous imbibition. At low interfacial tension, no significant snap-off is caused, but because of the lack of power, only the oil near the inlet can be effectively utilized and the other areas are hardly affected. However, at high interfacial tension, the spontaneous imbibition distance is long enough to utilize more oil, but because of the strong dynamics, the spontaneous imbibition front is unstable, which causes a more severe snap-off and generates more residual oil in each area. Based on the above observation, a compound interfacial tension method is proposed to reduce the snap-off and further improve the spontaneous imbibition recovery factor. The compound interfacial tension refers to the use of fluids with low and high interfacial tension in succession so that the advantages of both can be fully exploited. In this case, there is a significant reduction in the snap-off near the inlet, which also makes the spontaneous imbibition resistance reduced and the degree of utilization to the interior of the core increased.