Experimental investigation of nonequilibrium capillarity effects: Fluid viscosity effects

Abstract

[1] Numerical models have been widely used to simulate multiphase flow in porous media for a variety of applications (e.g., NAPL migration in subsurface aquifers, carbon sequestration, agriculture, paper production, and petroleum reservoir development). The relationship between the difference in phase pressures and saturation is used as one of the important constitutive relationships in numerical models. Theoretical studies have suggested that this relationship should include a damping coefficient or capillarity coefficient () on the basis of thermodynamic considerations. A literature review suggests that the magnitude of this capillarity coefficient varies by over three orders of magnitude. While recent experimental studies have explored the effect of porous medium properties, effect of domain size, hysteresis, and the imposed boundary conditions on the magnitude of , there has been no experimental study investigating the impact of fluid viscosity on . This study reports on a series of primary drainage experiments conducted under both static and dynamic conditions in F70 silica sand. Fluid pairs used included water and silicone oil with two differing viscosities and slightly different densities (used as model nonaqueous phase liquids) in addition to air. Water saturation and both wetting and nonwetting phase pressures were measured in a custom-built aluminum column using EC-5 probes and tensiometers at three levels. Results show a strong dependence of the magnitude of the capillarity coefficient on effective fluid viscosity. This implies that consideration should be given for the inclusion of a capillarity coefficient in modeling tools used to simulate multiphase flow when fluids saturations are changing rapidly and when fluids have a large viscosity ratio.

Scale dependency of dynamic relative permeability–satuartion curves in relation with fluid viscosity and dynamic capillary pressure effect

“…Pressures of both phases and water saturation were measured using tensiometers and EC-5 probes at three levels inside the domain. Das and Mirzaei [44] used two different sands with mean permeabilities of 8.7 9 10 -10 m 2 and 3.1 9 10 -10 m 2 along with water and silicone oil of viscosity 200 cSt which is higher than what [3] used. The results obtained in the two studies are different owing to not only porous medium properties (e.g., permeability, particle size) and fluid properties but also the domain size.…”

“…For example, the experimental results by Goel and O'Carroll [3] and Das and Mirzaei [44] on dynamic capillary pressure effects, namely the dynamic coefficient-saturation (s-S w ) relationships, provide some highlights on these factors as shown in Fig. 1.…”

“…This saturation-rate dependency of the system properties observed during non-steady state two-phase flow is referred to as dynamic capillary pressure effects [15] and a large body of literature involving experimental, modeling and theoretical studies has emerged concerning these phenomena [3,4,7,13,[15][16][17][18][19][20][21][22][23][24][25]. Studies by Stauffer [23], Kalaydjian [18], Hassanizadeh and Gray [26] suggest that an extension of the P c -S w function should include a saturation rate dependent term.…”

“…The results obtained in the two studies are different owing to not only porous medium properties (e.g., permeability, particle size) and fluid properties but also the domain size. While the domain in one study [3] was a cylindrical column 20 cm long and 10 cm inner diameter, in the other study [44] it was cylindrical column 12 cm long and 10.2 cm inner diameter. Therefore, we can understand that domain size is an important factor influencing dynamic effects in capillary pressure.…”

“…Both of the studies were conducted for primary drainage (PD) under quasi-static and dynamic conditions, i.e., in the cases when qS w /qt values are near and far from zero, respectively. Goel and O'Carroll [3] used F70 silica sand as porous media having a mean permeability of 1.42 9 10 -11 m 2 . Water and silicone oil with two differing viscosities (i.e.…”