Sorption-Induced Permeability Evolution and Chemo-Mechanical Interactions of CO2 Sequestration in the Marcellus Shale

Abstract Recognizing the limitations of conventional reservoirs, we were inspired to investigate the underexplored potential of organic-rich shales for secure geological storage. This began with the puzzling observation that permeability in the Marcellus Shale, under CO2 injection, declined in two distinct stages: an unexpected behavior inconsistent with simple Darcy flow. To unravel this, we designed a multi-pronged investigation to probe both pore-scale dynamics and molecular-level interactions driving this phenomenon. We first applied pulse-decay coreflooding under triaxial confinement, comparing the behavior of helium, methane, and CO2. This revealed that CO2 uniquely exhibited an initial sharp reduction in permeability (adsorption-driven), followed by further constriction due to matrix reorganization; a behavior absent in helium flooding and subdued in methane flooding. To understand the role of pore structure and surface properties, we conducted BET and BJH analyses, which revealed a slit-like mesoporous and microporous network optimal for CO2 adsorption. Rivetted by the irreversible nature of these changes, we employed Raman spectroscopy to monitor the evolution of kerogen structure. Post-injection spectra showed increased aromatic ordering and subtle molecular reorganization, corroborating our hypothesis that CO2 not only occupies pores but also chemically interacts with the matrix. This comprehensive approach revealed a sorption–chemo-mechanical mechanism: CO2 is first adsorbed onto abundant micropores and kerogen, then induces subtle matrix restructuring and pore throat constriction, locking itself in place. These findings provide a predictive framework that links dynamic flow behavior, mineral–organic interactions, and structural evolution, demonstrating the Marcellus Shale's capacity as both an adsorptive sink and a structurally responsive sequestration medium. This work advances our understanding of how molecular-scale processes manifest in macroscopic storage security.