Sx. Ma et al., EFFECT OF CONTACT-ANGLE ON DRAINAGE AND IMBIBITION IN REGULAR POLYGONAL TUBES, Colloids and surfaces. A, Physicochemical and engineering aspects, 117(3), 1996, pp. 273-291
Wettability and pore structure are primary factors in determining the
capillary behavior of porous media. A key characteristic of the pore s
tructure of real porous media is the angular corners of the pores. As
a model of pore structure, angular tubes are much more realistic than
the commonly used cylindrical tube model. However, their behavior is q
uite complicated because contact angle, corner angle, and the meniscus
in the corners are all variables. The Mayer and Stowe-Princen (MS-P)
theory of drainage, together with a detailed model of meniscus behavio
r in a corner during imbibition, enables the relationships between cap
illary pressure and saturation to be investigated as a function of con
tact angle and pore geometry. In this study, a general relationship be
tween contact angle, corner angle, liquid saturation, and the curvatur
e of a meniscus in the corner of an n-sided tube is derived. For any c
orner angle, there is a critical contact angle at which the meniscus b
ecomes fiat and the capillary pressure falls to zero. Drainage of poly
gonal tubes (having cross-sections such as equilateral triangles and s
quares) is analyzed as a function of contact angle using the MS-P theo
ry. For imbibition, there are two filling mechanisms: the tube can be
filled by a meniscus advancing along the tube or it can be filled by e
xpanding the menisci from the tube corners. For both mechanisms, the c
ontact angle is treated as having either zero or finite contact angle
hysteresis. Systematic changes in drainage and imbibition capillary pr
essure curves with contact angle are obtained. The results are qualita
tively consistent with several features of the behavior of natural por
ous media, including the effect of wettability on the displacement eff
iciency of crude oil by water.