Overpressure-Driven Permeability Enhancement of Porous Sandstone via Topological Optimization

The traditional geological view holds that overpressure resists mechanical compaction during sedimentary burial, keeping effective stress approximately constant and thereby passively preserving porosity and permeability in deep reservoirs. However, this assumption has relied predominantly on theoretical inference and struggles to explain a widespread geomechanical paradox: in many overpressured formations, the magnitude of permeability enhancement significantly outpaces the degree of porosity preservation. To decode this paradox, we conducted a fundamental proof-of-concept study utilizing high-pressure percolation coupled with in situ micro-CT and fractal analysis to dynamically simulate the effects of overpressure on porous sandstone under constant mean effective stress. The results reveal a counterintuitive phenomenon: while the global porosity remained fundamentally stable, the absolute permeability demonstrated a significant ~8% enhancement. Microstructural analysis indicates that this enhancement is driven by localized hydraulic wedging and the reactivation of sub-resolution throats acting as topological bridges. This active topological optimization physically and mathematically manifests as: (1) the massive reconnection of macroscopic isolated pores; (2) an enhanced space-filling capacity of the flow network, evidenced by an increased coordination number and 3D pore space fractal dimension (Df); and (3) the structural straightening of fluid pathways, rigorously quantified by a reduction in flow tortuosity and tortuosity fractal dimension (DT). These findings, derived from a single well-characterized sandstone sample, demonstrate that overpressure-driven permeability enhancement is a physically plausible mechanism in tight sandstones. This discovery offers a candidate physical explanation for the anomalously high permeability observed in certain deep overpressured reservoirs. However, the generalizability of these results to reservoirs with differing porosities, mineralogies, and diagenetic histories remains to be evaluated through multi-sample studies.