Multiscale characterization of pore–throat structures and flow mechanisms in low-permeability reservoirs

Introduction The study focuses on the characterization of pore–throat structures and flow mechanisms in low-permeability reservoirs. Due to complex microstructures and unclear non-linear flow behaviors, understanding and accurately modeling the relationship between pore structures and macroscopic flow characteristics is crucial for effective reservoir evaluation. Methods A comprehensive approach combining macroscopic physical property testing, microscopic pore–throat characterization, and digital rock simulation was adopted. Techniques such as mercury injection, nuclear magnetic resonance (NMR), and X-ray CT scanning were used for pore structure analysis, while lattice Boltzmann method (LBM) simulations were employed for flow behavior evaluation. Results The study reveals distinct differences in pore structure between the W1 and W2 blocks of the Weixinan Sag. The W1 block has well-connected intergranular dissolution pores, while the W2 block contains smaller intercrystalline pores with stronger adsorption effects, leading to reduced flow capacity. The results also show a clear relationship between microstructure and macroscopic flow behavior, with the W1 block showing better flow potential. Discussion The findings suggest that traditional reservoir classification methods may not sufficiently account for the complexities of low-permeability reservoirs. This study introduces a multi-parameter classification system based on pore-throat topology and non-Darcy flow characteristics, which can better predict high-quality reservoirs and guide differentiated development strategies.