Transp Porous Med (2011) 89:63–73 DOI 10.1007/s11242-011-9752-7 Capillary Pressure Curve for Liquid Menisci in a Cubic Assembly of Spherical Particles Below Irreducible Saturation Jacob Bear · Boris Rubinstein · Leonid Fel Received: 6 October 2010 / Accepted: 2 March 2011 / Published online: 30 March 2011 © Springer Science+Business Media B.V. 2011 Abstract The capillary pressure–saturation relationship, P c ( S w ), is an essential element in modeling two-phase flow in porous media (PM). In most practical cases of interest, this relationship, for a given PM, is obtained experimentally, due to the irregular shape of the void space. We present the P c ( S w ) curve obtained by basic considerations, albeit for a particular class of regular PM. We analyze the characteristics of the various segments of the capillary pressure curve. The main features are the behavior of the P c ( S w ) curve as the wetting-fluid saturation approaches zero, and as this saturation is increased beyond a certain critical value. We show that under certain conditions (contact angle, distance between spheres, and satura- tion), the value of the capillary pressure may change sign. Keywords Porous media · Two-phase flow · Wetting fluid · Capillary pressure curve List of Symbols d Distance between spheres n Number of spheres per unit cell H Mean curvature of meniscus P c Capillary pressure P w , P n Pressures in wetting and non-wetting fluids R Radius of sphere S w , S n Saturations of wetting and non-wetting fluids S wr , S nr Irreducible w-fluid and residual n-fluid saturations This article is dedicated to the memory of Prof. Walter Rose (1920–2009), a friend, engineer and scientist, who did pioneering work on the capillary pressure curve in reservoir engineering. J. Bear (B ) · L. Fel Department of Civil Engineering, Technion, 32000 Haifa, Israel e-mail: cvrbear@techunix.technion.ac.il B. Rubinstein Stowers Institute for Medical Research, Kansas City, MO 64110, USA 123