Mechanism of methane adsorption on groove space in organic matter surface

ABSTRACT

Organic matter plays an important role in methane adsorption in shale. Pore surface of organic matter is usually rough and uneven, which results in a large amount of groove space on the pore surface. Thus, the influence of groove space on the adsorption capacity of methane in shale cannot be neglected. Nanoscale pore structures of the organic-rich shale in the Longmaxi Formation were investigated by low-pressure nitrogen gas adsorption as a basis for constructing models. We simplified the internal groove space into triangular prisms with different angles. The grand canonical Monte Carlo simulation and molecular dynamics simulation were used to analyse the methane molecule adsorption behaviour in pores. The results showed that the pore morphology of organic-rich shale in the Longmaxi Formation was mainly slit-shaped pores. The excess adsorption isotherms showed good agreement between experiment and simulation, indicating that the model is suitable and reliable. Methane molecules can enter into the groove space with an opening size of 0.738 nm, while they fail to enter into groove spaces with an opening size less than 0.492 nm. This understanding has important significance for the study of the adsorption characteristics of organic pores which have undergone multiple evolutions in geological history.

KEYWORDS:

• Adsorption mechanism
• organic pore
• groove space on the pore surface
• molecular simulation

Additional information

Funding

This work was jointly supported by the National Natural Science Foundation of China (No. 41772141, 41402124), the Fundamental Research Funds for the Central Universities (No. 2017CXNL03), and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD).