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Analytical Solution of Gas Flow in Rough‐Walled Microfracture at In Situ Conditions
Author(s) -
Wang Junjian,
Tang Dazhen,
Jing Yu
Publication year - 2019
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2018wr024666
Subject(s) - knudsen number , knudsen flow , mechanics , flow (mathematics) , slip (aerodynamics) , real gas , flow coefficient , knudsen diffusion , tight gas , surface finish , geology , pressure gradient , permeability (electromagnetism) , materials science , geotechnical engineering , thermodynamics , chemistry , physics , hydraulic fracturing , composite material , biochemistry , membrane
The development of the unconventional gas and CO 2 sequestration is moving to deep formations. Because of the small flow pathways in the matrix, the Knudsen number might be high even though the gas is dense. In fact, due to the relatively high pressure at in situ conditions, gas flow in microfractures usually manifests a strong slip and nonideal gas effects. Therefore, understanding the coupling mechanism of these two on gas flow in rough‐walled microfractures is required to accurately model subsurface flow behavior. In this study, pressure‐driven gas flow in rough‐walled microfracture is analyzed in depth. Starting from the local governing equations for gas flow, a local flow model that includes gas slip and nonideal gas effects is derived by solving the Stokes equation with a first‐order slip boundary condition. Focusing at the representative elementary volume scale, the upscaled solutions to gas flow in a fracture with sinusoidal surface are derived to obtain the apparent permeability. The impact of nonideal gas effects, fracture roughness and aperture, and the tangential momentum accommodation coefficient on CH 4 and CO 2 flow is analyzed. The results show that fracture roughness introduces a high degree of heterogeneity in gas flow. At in situ conditions effects of gas slip, fracture roughness and tangential momentum accommodation coefficient on gas flow are reduced. The ideal gas law is capable of estimating CH 4 flow to some extent. However, it fails to estimate CO 2 flow in microfractures.