Pore–throat and fracture structures control heterogeneous fluid transport in volcanic reservoirs of the southern Songliao Basin

Abstract Deep volcanic gas reservoirs are widely distributed in the southern Songliao Basin, yet their exploitation is severely constrained by pronounced heterogeneity and complex pore–fracture architectures. To address this challenge, we developed an integrated approach combining multi-scale, high-resolution computed tomography (CT) modeling and grey relational analysis to quantitatively characterize the three-dimensional structures of total pores, connected pores, pore–throat networks, and fracture systems in representative volcanic samples. The results reveal substantial heterogeneity, with porosity ranging from 2.3% to 29.3% and permeability spanning six orders of magnitude (0.00017–9.25 mD). Flow simulations demonstrate that coupled fracture–pore–throat systems form continuous, low-resistance flow pathways, whereas dispersed pore structures exhibit pronounced bottleneck effects and reduced transport efficiency. Grey relational analysis further identifies the dominant controls on permeability, showing that fracture attributes predominate in high-permeability samples, whereas pore–throat characteristics dominate in low-permeability samples. Accordingly, two distinct seepage regimes are identified: fracture-enhanced flow with pore–throat synergy and pore–throat-dominated flow. This study establishes a microstructure-based framework for classifying and evaluating heterogeneous tight reservoirs, providing insights into the pore–fracture controls on fluid transport and technical guidance for efficient gas development.