Study on Pore Structures of Tight Sandstone Reservoirs Based on Nitrogen Adsorption, High-Pressure Mercury Intrusion, and Rate-Controlled Mercury Intrusion

Abstract

Pore–throat size is a key parameter for the assessment of reservoirs. Tight sandstone has the strong heterogeneity in the distribution of pores and throats; consequently, it is very difficult to characterize their distributions. In this study, the existing pore–throat characterization techniques were used jointly with scanning electron microscopy (SEM), low-temperature nitrogen adsorption (LTNA), high-pressure mercury intrusion (HPMI), and rate-controlled mercury intrusion (RCMI) technologies to highlight features of throat sizes and distribution of pores in tight sandstone reservoirs of the Y Basin in China. In addition, full-scale maps (FSMs) were generated. The study results show that key pore types in reservoirs of the Y Basin include residual intergranular pores, dissolved pores, clay mineral pores, and microfractures. LTNA can effectively characterize the distribution of pore–throats with a radius of 2–25 nm. HPMI test results show that tight sandstones contain throats with a radius less than 1000 nm, which are mainly distributed in 25–400 nm and have a unimodal distribution. RCMI tests show that there is no significant difference in pore radius distribution of the tight sandstones, peaking at approximately 100,000–200,000 nm; the throat radius of tight sandstones varies greatly and is less than 1000 nm, in agreement with that of HPMI. Generally, the pore–throat radius distribution of tight sandstones is relatively concentrated. By using the aforementioned techniques, FSM distribution features of pore–throat radius in tight sandstone can be characterized effectively. G6 tight sandstone samples develop pores and throats with a radius of 2–350,000 nm, and the pore–throat types of tight sandstone reservoirs in Y basin are mainly mesopores and macropores.