Pore-Scale Insight of Tight Core Pressurized Imbibition: Impacts of Pressure, Interfacial Tension, and Pore-Throat Connectivity

Imbibition is a promising mechanism for enhancing tight oil recovery; however, the influences of several key factors remain controversial, and the governing mechanisms are not fully understood. In this study, pressurized imbibition experiments were conducted on tight cores from the Yanchang Group to systematically evaluate the effects of pressure, interfacial tension (IFT), and permeability. Pores within tight cores were first classified into four distinct categories by correlating high-pressure mercury-intrusion pore size with the nuclear magnetic resonance (NMR) transverse relaxation time. The contribution of each pore type was thereafter quantitatively distinguished by tracking the changes in NMR spectra, and the optimal imbibition conditions were identified. Experimental results indicate that (1) imbibition efficiency increases with increasing pore-throat connectivity under optimized conditions. (2) Nanopores and micropores are the dominant contributors in tight core imbibition. (3) A moderate increase in pressure enhances tight core imbibition, and the optimal pressure rises with improving pore-throat connectivity. (4) The sensitivity of different pores to IFT is strongly dependent on the physical properties of the cores. Maximizing the utilization of nanopores while balancing the contributions of other pores is essential for achieving satisfying imbibition efficiency with tight cores. (5) A relatively lower IFT is preferable to compensate for the reductions in pore size and pore-throat connectivity when the pressure increases. These findings provide practical guidance for selecting an appropriate energy-replenishment coefficient and for designing imbibition fluids tailored to the varying pressure scenarios encountered in tight oil reservoirs.