Investigation on Imbibition Mechanism of Tight Core Based on NMR Test

[Image: see text] Seepage is important to improve the postpressure production enhancement effect of tight oil and gas reservoirs. To study the microscopic percolation law of different pores, this paper first characterizes the pore structure of tight cores. High-pressure spontaneous percolation experiments and nuclear magnetic resonance (NMR) tests were combined. The T(2) spectra at different times of percolation were used. The percolation law of different pore types was quantitatively characterized from a microscopic perspective. The effect of different interfacial tensions on the percolation was clarified. Results show that the pore size has a good match with the NMR T(2) relaxation time. The core pore development is dominated by submicrometer pores, which account for more than 70%. The percolation rate is fast at the beginning and then decreases and stabilizes at 48 h. The pore size of the submicropore is small, the capillary force is large, and the recovery rate of percolation is high, followed by those of the micropore and the medium-pore. The higher the porosity and permeability of the core, the greater the overall seepage recovery rate. The sensitivity of submicrometer pores to interfacial tension is great, and the recovery rate increases by 40.9% when the interfacial tension decreases from 17.1 to 1.46 mN/m. Furthermore, as the interfacial tension decreases, the recovery rate of different pores appears to increase first and then decrease. The surfactant formulation must be selected reasonably in practical production.