Dual-scale insights of two-phase flow in inter-cleats based on microfluidics: Interface jumps and energy dissipation
Jicheng Zhang, Dawei Lv, Jincai Zhang, Feng Wang, Dawei Yin, Haiyang Yu
Abstract
Cleat serves as the primary flow pathway for coalbed methane (CBM) and water. However, few studies consider the impact of local contact on two-phase flow within cleats. A visual generalized model of endogenous cleats was constructed based on microfluidics. A microscopic and mesoscopic observation technique was proposed to simultaneously capture gas–liquid interface morphology of pores and throat and the two-phase flow characteristics in entire cleat system. The local contact characteristics of cleats reduced absolute permeability, which resulted in a sharp increase in the starting pressure. The reduced gas flow capacity narrowed the co-infiltration area and decreased water saturation at the isotonic point in a hydrophilic environment. The increased local contact area of cleats weakened gas phase flow capacity and narrowed the co-infiltration area. Jumping events occurred in methane-water flow due to altered porosity caused by local contact in cleats. The distribution of residual phases changed the jumping direction on the micro-scale as well as the dominant channel on the mesoscale. Besides, jumping events caused additional energy dissipation, which was ignored in traditional two-phase flow models. This might contribute to the overestimation of relative permeability. The work provides new methods and insights for investigating unsaturated flow in complex porous media.