Multiscale Quantitative Characterization of Basalt Pore and Throat Networks Using Micro-CT: Implications for Connectivity-Controlled Permeability

Abstract

Pore−throat structure and connectivity are critical controls on injectivity and fluid migration in basalt CO2 storage reservoirs. This study quantitatively characterized the pore−throat structure in Cenozoic basalt matrix samples from southeastern China by integrating high-resolution micro-CT imaging, three-dimensional reconstruction, and pore-network modeling. Core-scale measurements show that the basalt has relatively high porosity (23.96%) but extremely low permeability (0.07 mD), indicating that macroscopic pore storage does not necessarily translate into effective flow pathways. At the matrix scale, the micro-CT-resolved total porosity is 3.99%, whereas connected porosity is only 0.68%, indicating weak overall connectivity of the matrix pore system. Abundant small-diameter pores mainly occur as isolated pores, dead-end branches, or locally disconnected pore clusters and contribute little to continuous flow. Effective connectivity is mainly concentrated in a sparse pore−throat backbone composed of a limited number of larger pore bodies and open pore throats. Pore bodies with diameters greater than 15 μm make a more important contribution to potential flow capacity, whereas mineral filling, narrow throats, and local bottlenecks further restrict pore−throat continuity. Overall, this study proposes a connected-backbone-controlled potential seepage model for the basalt matrix. This model emphasizes that flow capacity is not controlled simply by total porosity but mainly depends on whether larger pore bodies and open pore throats can form a continuous connected backbone. This understanding provides a basis for initial pore−throat structure evaluation, injectivity potential assessment, and effective flow-pathway identification in basalt CO2 storage reservoirs.