Capillary trapping induced slow evaporation in nanochannels

Unconventional reservoirs are massive and providing an increasing share of global energy with a broad group of stakeholders in academia, industry and government. The size of pores in unconventional reservoirs can be down to nanometers, necessitating a deeper fundamental understanding of fluid phase properties at nanoscale. In this paper, we investigate capillary trapping induced slow evaporation of n-pentane in nanochannel arrays through isothermal pressure drawdown to mimic the hydrocarbon release in nanopores of low-permeability reservoirs. Importantly, the capillary trapping forms during a slow reservoir pressure reduction process and significantly impedes liquid evaporation. Compared to the evaporation case without any capillary trapping, the global evaporation rate is similar to 16 times lower, which unfavorably affects gas recovery. In addition, we observe liquid corner flow in assisting evaporation in nanochannel, providing important experimental evidence towards previous theoretical study. In brief, our work reveals a type of anomalous evaporation at nanoscale that is fundamentally relevant to shale gas recovery. The experimental and modeling finding indicates that regulating pressure drawdown at an appropriate rate plays a key role in efficiently extracting shale gas.

Automated summary

This study explores the slow evaporation of n-pentane in nanochannel arrays in unconventional reservoirs induced by capillary trapping, which significantly hinders liquid evaporation and reduces the global evaporation rate by approximately 16 times compared to cases without capillary trapping. The findings suggest that regulating pressure drawdown at an appropriate rate plays a crucial role in efficiently extracting shale gas.