Abstract: To address the problem of unclear microscopic pore structure characteristics of tight sandstone in Block XAB, by using the experiments such as high-pressure mercury injection (HPMI), nuclear magnetic resonance (NMR), cast thin section (CTS) and scanning electron microscopy (SEM), the microscopic pore distribution and connectivity characteristics of tight sandstone reservoirs in Block XAB was studied; the relationship between parameters such as effective pore throat radius, effective porosity and effective movable porosity and macroscopic physical properties was clarified, and the microscopic and macroscopic characteristics of typical pore structure reservoirs was identified and evaluated. The results of the study show that the target reservoir had many pore types and a wide range of pore sizes, but the overall pore size was less than 2 μm, and the pore throat was dominated by large pore-fine throat ink bottle type connectivity; the pore throat with pore size larger than the effective pore throat radius had a small proportion of the total pore volume, but it contributed more than 90% to the permeability; the pore size distribution range measured by NMR was wider than that of HPMI, and the effective movable porosity excluded the existence of unmovable water in the isolated large pores; there was a strong positive correlation with the effective porosity obtained by HPMI, and a high index relationship with the permeability; the pore throat radius had an important role in controlling the microscopic pore structure and macroscopic reservoir quality; the target reservoir pore structure can be classified into three types, i.e., type Ⅰ, Ⅱ and Ⅲ, and the average effective movable porosity was 2.93%, 0.78% and 0.15%, respectively, as the reservoir pore structure parameters became worse. The study results are of great significance for the effective evaluation of the target reservoir and its efficient development.

Key words: dense sandstone, pore structure, NMR, porosity, pore throat radius, reservoir evaluation