EXPERIMENTAL STUDY ON THE DIFFERENCE OF MICROPORE STRUCTURE CHARACTERISTICS AND ITS GENESIS IN LOW-PERMEABILITY SANDSTONE UNDER DIFFERENT PORE THROAT MATCHING CONDITIONS

The study of pore structure and genesis of low-permeability tight sandstone reservoirs is a hot spot in geoscience research. In this paper, taking the Jurassic Xishanyao Formation, Toutunhe Formation, and Qigu Formation tight sandstone reservoirs in the Niuquanhu block of the Santanghu Basin as examples, the differences in micropore pore throat characteristics and their genesis of low-permeability tight sandstone reservoirs were systematically analyzed based on petrophysical property tests, core cast thin sections, scanning electron microscopy, and constant speed mercury injection test results. The results show that the Xishanyao Formation mainly develops primary intergranular pores and intercrystalline dissolution pores, and the throats appears in a sheet-like and curved sheet-like types. In the reservoirs of the Toutunhe Formation and Qigu Formation, intergranular pores are mainly developed, followed by dissolution pores, and the throats showed constricted neck-like, spot-like, and sheetlike features. The pore parameters of the reservoirs in the three formations are not significantly different, but the throat parameters are very different. The hydrodynamic action in the Xishanyao Formation is weak, the parent rock is weak in weathering resistance, the content of rock debris is high, and the degree of compaction is also high. However, the distribution range of throat radius in the Toutunhe Formation and Qigu Formation is relatively wide, and the content of large throats is significantly higher. Under the condition of the same permeability, the throat radius of the sandstone reservoir of the Xishanyao Formation is small and the distribution range is relatively concentrated, and its pore throat ratio is larger than that of the other two formations. Sedimentary hydrodynamic conditions, particle size, rock debris and matrix composition, diagenesis types, and degree of transformation are the main reasons for the differences in the degree of pore development, throat types, and pore throat parameters among different reservoirs.