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The nanoconfinement effect, induced by strong surface−molecule interactions at the nanoscale, is correlated only to the pore size from a traditional perspective. However, when the pore size is comparable to the molecular diameter, the impact of surface wettability on the surface−molecule interaction strength cannot be overlooked. In order to bridge the knowledge gap, in this article, the nanoconfinement effect is described as a function of not only pore size shrinkage but also surface wettability. The Peng− Robinson equation of state is modified by adding a fluid−surface attraction term, incorporating the shift of critical properties induced by surface affinity. Particularly, the wettability effect is described as a function of contact angle, an easily accessed macroscopic parameter, facilitating the model application. Reliability of this research is verified against shifted fluid critical properties, collected from existing reports, focusing on fluid behavior in graphite or mica nanopores. The results show that (a) reduction of methane critical temperature takes place when methane molecules are confined in hydrocarbon-wet nanopores; (b) both the enhancement of surface affinity and decline of pore size will result in the shrinkage of the methane liquid−vapor coexistence curve; and (c) the phase diagram of nanoconfined methane suggests an upward trend, attributed to the shifted critical properties. In this article, the wettability effect on nanoconfined methane behavior is revealed, expecting to enrich the theoretical background about methane behavior inside nanopores.

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Original scientific paper https://doi.org/10.2298/TSCI171218162WThe aggregation of coal fines particles at the bottom of the coal-bed methane well is a common occurrence during production, which could inhibit the flow in the bottom of wells and have adverse effect on the downhole equipment. In this work, gas-liquid-solid three-phase flow experiments were carried out to investigate the migration and discharge of coal fines particles in undulating pipeline. The experiments were conducted in downbent V-shaped pipes with different inclination angles. Based on the conductivity method, the real-time liquid holdup at three positions of the elbow was measured by the developed software. The slugs were identified on the time series curves of liquid holdup, and the characteristics of each slug were calculated, such as length and translational velocity. Meanwhile, the moving of particles with different size and concentration can be observed through visualized flow channel. The dyed coal fines particles are injected into the multiphase flow loop. By observing whether they can be discharged from the V-shaped pipe, the lower limits of superficial gas and liquid velocities to avoid particle retention at the elbow were determined. A correlation to predict the critical gas and liquid velocity was presented, and the accuracy of the calculation model was verified in comparison with the experimental results.

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