Since methane is an important component of shale gas, its confined phase behavior is significant to understand the essential mechanism leading to the fluid occurrence and hydrocarbons production. We studied the confinement impact of shale inorganic nanopores with pore sizes of 2–20 nm, for temperatures at phase equilibrium (120–190 K) and reservoir condition (325 K) using Monte Carlo molecular simulations. Compared with the bulk, the adsorption increases the equilibrium gas density, while the capillary condensation reduces the liquid density and equilibrium pressure, and the effect of adsorption is more significant. Affected by the equilibrium phase change, the methane reaches the critical point under lower temperature and pressure in inorganic nanopores. We fitted the critical shifts and explored the impact of pore width and wall material on fluid properties (phase density, equilibrium pressure, critical parameter, and density distribution). The confinement effect is positively correlated with the interaction between mineral composition and methane while decreases with the increasing pore width. In both phase equilibrium and reservoir conditions, the phase behavior in different mineral slits is significantly different, especially in the pores less than 10 nm. The confined phase equilibrium of methane is related to the pore pressure, and is not affected by the size and wall material of other pores. This research has a better insight into the phase behavior of methane in shale inorganic materials, and provides support for the phase equilibrium calculation of single pore and the upgrade of multiple pore sizes.

由于甲烷是页岩气的重要组成部分，其受限相行为对于理解导致流体赋存和烃类生产的基本机制具有重要意义。我们使用蒙特卡罗分子模拟研究了孔径为 2-20 nm 的页岩无机纳米孔对相平衡温度（120-190 K）和储层条件（325 K）的限制影响。与本体相比，吸附增加了平衡气体密度，而毛细管冷凝降低液体密度和平衡压力，吸附效果更显着。受平衡相变的影响，甲烷在无机纳米孔中在较低的温度和压力下达到临界点。我们拟合了临界位移，并探索了孔隙宽度和壁材对流体特性（相密度、平衡压力、临界参数和密度分布）的影响。限制效应与矿物成分和甲烷之间的相互作用呈正相关，而随着孔隙宽度的增加而减小。在相平衡和储层条件下，不同矿物狭缝中的相行为明显不同，尤其是在小于 10 nm 的孔隙中。甲烷的受限相平衡与孔隙压力，不受其他孔隙大小和壁材的影响。该研究更好地洞察了页岩无机材料中甲烷的相行为，为单孔相平衡计算和多孔径升级提供了支持。