(593e) Phase Transition and Criticality of Methane Confined in Nanopores

The aim of this study is to experimentally and theoretically investigate the phase transition and criticality of methane confined in nanoporous media. Although methane is the most dominant component of natural gas in unconventional reservoirs, such a study has never been done before, except for the deuterated methane at atmospheric pressure. The investigation is performed by establishing an experimental setup, which is composed of a differential scanning calorimeter (DSC) capable of operating under very low temperatures as well as high pressures to detect the capillary phase transition of methane inside the pores. By performing experiments along isochoric cooling paths, both the capillary condensation and the bulk condensation of methane are detectable. The pore critical point (PCP) of nanoconfined methane is also measurable. Furthermore, a previously developed self-consistent equation of state (EOS) based on the generalized van der Waals (vdW) partition function, the parameters of which are directly derived from the experimental PCP, is applied to predict the capillary-condensation curves and matched with the experimental data. The EOS is superior to conventional EOS in its self-consistency without needing an auxiliary equation, such as the Young-Laplace equation. The experimentally determined phase behavior of nanoconfined fluids and the self-consistent EOS are both significant for a wide range of scientific and engineering applications, including the separation science and the flow simulation of hydrocarbons in shale and tight reservoirs.