Wettability Impact on Nanoconfined Methane Adsorption Behavior: A Simplified Local Density Investigation

The key to unlock huge economic benefits from shale gas reservoirs is to reveal the methane adsorption behavior in nanopores. A clear understanding of nanoconfined methane adsorption behavior will dramatically mitigate the imbalance between energy supply and demand over the world, which remains a challenge and entails in-depth investigation. To the current knowledge, specific materials, like graphene layers, quartz, and feldspar, are utilized to mimic an organic or inorganic solid phase in shale, while the shale physical composition is complex and evidently cannot be represented by one or several identified compositions. In this paper, to bridge the knowledge gap, the wettability effect, embodied by the surface contact angle, is correlated to the nanoconfined methane adsorption behavior for the first time. Because the solid-phase composition variation will result in alteration of the contact angle regarding the solid-methane system, the incorporation of the surface contact angle enables this research to cover a wide range of solid composition variations. First, the relationship between solid-fluid interactions and the surface contact angle is revealed. Then, the simplified local density method is proposed by coupling the relationship upon the surface contact angle, and also the shift of methane critical properties induced by the nanoconfinement effect is considered. Results show that (a) the ratio of bulk methane to nanoconfined average density ranges from 0.55 to 0.71 with increasing pressure, (b) adsorption peak density can enhance up to 3 times by manipulating the solid-phase wettability effect, and (c) the adsorption capacity in organic-rich shale is 1.72 times that in inorganic-rich shale. The research provides a profound theoretical framework to elucidate the methane adsorption mechanism in nanopores and serves as a robust tool to reproduce and predict the methane adsorption behavior.

Automated summary

This paper correlates the nanoconfined methane adsorption behavior with the wettability effect for the first time, providing a theoretical framework and research tool for elucidating the methane adsorption mechanism in nanopores.