Experimental investigation on dynamic imbibition characteristics of imbibition agent and influencing factors in low-permeability reservoir with nuclear magnetic resonance

Dynamic imbibition significantly contributes to the hydrocarbon extraction from low-permeability reservoir formations. This research investigates fluid migration phenomena across varying pore dimensions. Integrating mercury intrusion porosimetry with nuclear magnetic resonance (NMR), we quantified the T2 relaxation and pore dimension relationship for classification of three pore size categories. Core flood apparatus-driven dynamic imbibition assessments were conducted to quantitatively characterize oil migration mechanisms. Furthermore, synchrotron NMR analysis revealed that injection rate, permeability, and soaking time impact oil mobilization efficiencies across different pore sizes. The results show that macropores predominantly govern the oil recovery and mesopores exhibit the phenomenon of negative convection. In contrast to formation water, imbibition agent can produce oil from micropores. Synergistic interplay between viscous and capillary forces governs fluid redistribution in porous media throughout the dynamic imbibition process. Under reduced injection rate, the displacement effect is relatively weak, and the degree of oil migration in micropores is high. Increased permeability enhances oil mobilization efficiency across macropores, micropores, and entire pores. During the early stage of soaking, oil migration from mesopores and macropores is significant. In addition, prolonging the soaking time is beneficial for capillary-dominated oil extraction from micropores. This investigation provides critical insights for the development of enhanced oil recovery from unconventional reservoirs.