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On two‐phase relative permeability and capillary pressure of rough‐walled rock fractures
Author(s) -
Pruess K.,
Tsang Y. W.
Publication year - 1990
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/wr026i009p01915
Subject(s) - relative permeability , capillary pressure , wetting , mechanics , permeability (electromagnetism) , porous medium , capillary action , multiphase flow , geology , two phase flow , plane (geometry) , porosity , geotechnical engineering , materials science , geometry , mineralogy , flow (mathematics) , mathematics , chemistry , composite material , physics , biochemistry , membrane
This paper presents a conceptual and numerical model of multiphase flow in fractures. The void space of real rough‐walled rock fractures is conceptualized as a two‐dimensional heterogeneous porous medium, characterized by aperture as a function of position in the fracture plane. Portions of a fracture are occupied by wetting and nonwetting phase, respectively, according to local capillary pressure and global accessibility criteria. Phase occupancy and permeability are derived by assuming a parallel‐plate approximation for suitably small subregions in the fracture plane. For lognormal aperture distributions, a simple approximation to fracture capillary pressure is obtained in closed form; it is found to resemble the typical shape of Leverett's j function. Approximations to wetting and nonwetting phase relative permeabilities are calculated by numerically simulating single phase flows separately in the wetted and nonwetted pore spaces. Illustrative examples indicate that relative permeabilities depend sensitively on the nature and range of spatial correlation between apertures. It is also observed that interference between fluid phases flowing in a fracture tends to be strong, with the sum of wetting and nonwetting phase relative permeabilities being considerably less than 1 at intermediate saturations.