Cross-scale diffusion characteristics in microscale fractures of tight and shale gas reservoirs considering real gas – mixture – body diffusion – water film coupling

Abstract

The mechanism of solid fluid coupling in unconventional oil and gas reservoirs is complex, and elucidating the characteristics of cross scale gas seepage has important scientific and engineering significance. This article focuses on the gas seepage characteristics in micro fractures of unconventional natural gas reservoirs, with three main innovations: (a) analyzing the coupling mode between real gas effects and mixed gases; (b) Explored the multi factor control mechanism of bulk gas diffusion in microscale fractures; (c) The mechanism of the influence of water film distribution characteristics in microscale fractures on gas seepage was elucidated. Results show that: (a) For the water saturation of 10% and the methane content of 80%, when the gas pressure in the crack increased from 0.2 MPa to 10 MPa, the continuous flow velocity and slippage flow velocity increased. (b) for the water saturation of 10% and the methane content of 80%, when the mixed gas pressure increases from 0.2 MPa to 0.8 MPa, the bulk gas diffusion rate drops relatively rapidly from 8.40E-22 kg/s to 8.18E-23 kg/s (c) for the water saturation of 10% and the methane content of 80%, when the mixed gas pressure increases from 0.2 MPa to 0.6 MPa, the modified slippage flow rate drops relatively rapidly from 7.47E-21 kg/s to 6.96E-21 kg/s.