Abstract
Imbibition in glass micromodels for air-mercury and water-oil systems occurs by wetting phase (wp) cluster growth and frontal drive processes. Lower capillary number and higher wetting phase (wp) saturation at the start of imbibition favour cluster growth.
Imbibition experiments for both fluid systems show that the ‘rules’ of nwp withdrawal are related to pore size and to fluid topology as well as to aspect ratio. The emptying of a pore is favoured by small size, small aspect ratio (size ‘rules’), and fewer connected throats occupied by nonwetting phase (nwp) (fluid topology ‘rules’).
The relative importance of fluid topology compared with pore size in determining the sequence of nwp withdrawal from pores is affected by the initial nwp saturation, pore size variability, pore-throat size ratio, pore and throat shape and contact angle. High initial nwp saturation, small variability of pore size and small pore-throat diameter ratio are all factors which increase the effects of fluid topology in determining nwp withdrawal sequence. Under these conditions, nwp displacement efficiency is larger because withdrawal occurs first from ‘dead-end’ branches without breaking the continuity of the nwp conducting pathways to the nwp sink. The high nwp displacement efficiency obtained in unconsolidated sands may be explained by the importance of topology ‘rules’ during imbibition in these low aspect ratio media.
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Abbreviations
- D :
-
effective diameter of pore or throat given by 2 ÷F(ε)(1/x + 1/y),m
- F(ε) :
-
nondimensional term which varies as a function of cross-sectional shape (Lenormandet al., 1983)
- L :
-
external dimension of the network (width or length), m
- N ca :
-
capillary number in the network, dimensionless
- nwp:
-
nonwetting phase
- P :
-
any capillary pressure, Pa
- P I1:
-
apillary pressure for nwp to withdraw from a pore which has one connected throat occupied by nwp, Pa
- P I2:
-
capillary pressure for nwp to withdraw from a pore which has two adjacent connected throats occupied by nwp, Pa
- Q :
-
total volume flow rate in the network, m3/s
- S wi :
-
percent of pore volume occupied by wp at the end of drainage and start of imbibition, dimensionless
- S ni :
-
percent of pore volume occupied by nwp at the end of drainage and start of imbibition, i.e. 100 -S wi, dimensionless
- S nr :
-
percent of pore volume occupied by trapped nwp at the end of imbibition, dimensionless
- v :
-
velocity, m/s
- wp:
-
wetting phase
- X I :
-
diameter ofI2 interface in plan, m
- X P :
-
diameter of pore in plan, m
- X T :
-
width of throat, m
- Y P :
-
depth of pore, m
- Y T :
-
depth of throat, m
- Z :
-
number of throats connected to each pore (coordination number)
- γ :
-
interfacial tension, N/m
- θ :
-
contact angle, degrees
- μ :
-
viscosity, Pa · s
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Wardlaw, N.C., Yu, L. Fluid topology, pore size and aspect ratio during imbibition. Transp Porous Med 3, 17–34 (1988). https://doi.org/10.1007/BF00222684
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DOI: https://doi.org/10.1007/BF00222684