Physical experimental study on single-phase gas flow laws in 3D large-scale rock samples of ultradeep fractured tight sandstone gas reservoirs

Abstract

Ultra-deep fractured tight sandstone gas reservoirs in the Tarim Basin, China, feature extreme burial depth, low matrix porosity and permeability, complex high-temperature, high-pressure and high in-situ stress geological conditions, and heterogeneous multi-scale fracture development, which severely restricts efficient exploitation of gas reservoirs. To overcome these challenges, this study independently developed a THMC coupled physical experimental platform and established corresponding 3D large-scale rock sample physical experimental methodologies to simulate the reservoirs’ high-temperature and high-pressure in-situ conditions. In accordance with similarity criteria, 260 mm × 260 mm × 260 mm three-dimensional large-scale rock specimens were prepared, enabling accurate characterization of the complex reservoir system consisting of “pores–small fractures–large fractures”. Pressure probes were installed in both the matrix blocks and fractures of the three-dimensional large-scale rock samples to realize dynamic monitoring of pressure evolution. On the basis of this physical experimental technique, a physical simulation experiment of single-phase gas depletion production was performed. The results show that gas in large fractures is first produced in the early production stage, with subsequent gas recovery from small fractures and the matrix blocks adjoining large fractures. This reveals the distinctive seepage characteristics of ultra-deep fractured tight sandstone gas reservoirs in development, specifically the stepwise activation and coupled superposition of the large-fracture, small-fracture, and matrix block systems, which provides important technical guidance for the efficient development of this category of gas reservoirs.