Numerical Simulations of Methane Flow Characteristics in Water-Bearing Propped Hydraulic Fractures

Hydraulic fracturing produces propped fractures for the purpose of achieving higher permeability in coal reservoirs. The methane flow characteristics in closed propped fractures under water-bearing conditions will affect coalbed methane (CBM) production. In this study, the temporal and spatial evolution of the methane flow characteristics in water-bearing propped fractures was investigated. The results revealed that during water displacement by methane, the average velocity of methane first showed sharp increases and then gradual increases, with the average velocity of water decreasing along the horizontal flow direction of the methane. It was observed that the average velocity of water was greater than the methane velocity changed to the average velocity of the water was less than the methane velocity at a critical time, which indicated that the methane was carried by the water via a promotional relationship changed to water was pushed by the methane via a hindering relationship. The majority of methane was found to have migrated upward due to its low-gravity characteristics, which resulted in high concentrations of methane and low-density levels within the top spaces of water-bearing propped fractures. The rising and floating of methane resulted in higher displacement pressure gradients on methane-water interfaces, as well as greater velocity levels for methane and decreasing pressure levels from the bottom to the top layers in water-bearing propped fractures. Obvious methane flow was observed to have formed with higher methane concentrations and greater velocity levels within the top spaces of water-bearing propped fractures.