Occurrence states of organic matter modulate the surface properties of shale nanopores
Abstract
The surface properties of shale nanopores, governed by the coexistence of mineral surfaces and adsorbed organic matter, fundamentally controls ffuid invasion, occurrence, and mobility in conffned spaces and is therefore critical for shale oil and gas recovery. However, the individual contributions of organic matter with different occurrence states to wettability and surface potential remain poorly quantiffed. In this work, these contributions were decoupled using successive dichloromethane extraction and sodium hypochlorite oxidation, combined with multiple geochemical and petrophysical characterization methods. Experimental results conffrmed progressive organic matter removal and the liberation of pore wall surfaces. The removal of solvent-extractable organic matter reduces the water contact angle, while that of organic matter through subsequent oxidation causes further reduction. Surface potential measurements also revealed that the removal of organic matter with different occurrence states exerts distinct effects on the electrochemical properties of pore walls. Work of adhesion calculations indicated an increasing trend during progressive organic matter removal, quantitatively linking organic matter occurrence to interfacial free energy. The observed ffuid imbibition behavior demonstrated that invasion into sub100 nm pores is selectively hindered by residual organic matter, and the second-stage imbibition rate correlates positively with wettability. These ffndings establish a quantitative link between organic matter adsorption states and nanoscale interfacial properties, they providing a mechanistic framework for predicting ffuid behavior in organic rich shales and offering theoretical support for understanding shale wettability alteration and optimizing surfactant selection.
Document Type: Original article
Cited as: Li, X., Cai, J., Liu, H., Li, J., Li, Z., Cai, J. Occurrence states of organic matter modulate the surface properties of shale nanopores. Advances in Geo-Energy Research, 2026, 22(2): 103-117. https://doi.org/10.46690/ager.2026.11.02
DOI:
https://doi.org/10.46690/ager.2026.11.02Keywords:
Wettability, surface potential, organic matter occurrence states, shale nanopores, fuid invasionReferences
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