ABSTRACT
The strong reservoir heterogeneity and complex microscopic pore structure in the Linxing area make it prone to water block damage during imbibition development. In order to explore the influence of reservoir microscopic characteristics on imbibition efficiency, taking the tight sandstone gas reservoir in the Linxing area of Ordos Basin as an example, the heterogeneity of the tight sandstone reservoir in the study area is characterized in terms of physical and chemical characteristics as well as the microscopic pore structure. Using nuclear magnetic resonance, high-pressure mercury pressure, and other testing methods, spontaneous seepage experiments in real sandstone were carried out to study the distribution law of different pore structures and seepage characteristics at different times and to systematically evaluate the microscopic pore characteristics of dense sandstone reservoirs and the factors affecting seepage and suction. The results show that due to the strong microscopic heterogeneity of tight sandstone, the macroscopic properties cannot directly reflect the microscopic characteristics, and the response to imbibition efficiency is stronger. The pore size is the main controlling factor affecting imbibition, and the contribution rate of the micropore and mesopore mainstream pore size spaces is higher than that of the macropore. Micropores provide imbibition power, and mesopores provide an imbibition interval. High-porosity and high permeability reservoirs are more conducive to imbibition replacement. The intercrystalline pores have a great influence on the imbibition efficiency, and the influence of intergranular pores and dissolution pores on the imbibition cannot be underestimated. The smaller the relative sorting coefficient, interfacial tension, and contact angle, the better the imbibition effect of fracturing fluid. Research results have theoretical guiding significance for spontaneous imbibition to improve oil recovery.
