Dynamic capillary effects in a small‐volume unsaturated porous medium: Implications of sensor response and gas pressure gradients for understanding system dependencies

Abstract

.[1] Rate dependencies in system properties observed during nonsteady state unsaturated and multiphase flow are often referred to as dynamic capillary effects. One widely studied dynamic capillary effect is the apparent dependence of measured capillary pressure on the rate of saturation change. While this phenomenon has been observed for over four decades, a clear picture of the source of the phenomenon and its true magnitude remains elusive. Furthermore, reported dependencies on system properties and state variables have been contradictory. The focus of this work was on quantifying the relationship between measured capillary pressure and rate of saturation change using a small volume system with highly characterized fluid-selective microsensors. Experimental measurements in three systems were used to calculate the dynamic capillary coefficient as a function of saturation during drainage. Corrections for sensor response and flow-induced gas pressure gradients were applied to explore how these potential artifacts would impact measured values. Significant differences in values were observed in uncorrected measurement between the three systems, but corrected values were very similar in all cases. Corrected values were found to be on the order of 10 3 Pa s or less-one to two orders of magnitude lower than the uncorrected values, and two or more orders of magnitude lower than most published values for similar porous medium/fluid combinations. Because of the small size of the experimental system used, results suggest that at the representative elementary volume (REV) scale, the dependence of measured capillary pressure on the rate of saturation change may not be as significant as previously thought for unsaturated systems. It is hypothesized that the larger magnitude of some previously reported values may result at least in part from porous medium packing microheterogeneities that influence flow and pressure gradients in larger systems.Citation: Hou, L., L. Chen, and T. C. G. Kibbey (2012), Dynamic capillary effects in a small-volume unsaturated porous medium: Implications of sensor response and gas pressure gradients for understanding system dependencies, Water Resour.

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

“…Since for a saturation of 50 %, the value of mobility ratio is more than 1, the fluid fronts are considered to be stable. The trend observed here are similar to as observed by [2,13], i.e., as m decreases s increases at a given saturation.…”

“…For example, for the P c -S w relationships and their saturation-rate dependency, depend on factors such as fluid properties like viscosity and density ratios [2][3][4][5], domain scale [6][7][8][9], media permeability [7,10,11], micro-heterogeneities [9,12], and hysteresis in P c -S w relationships [9], among others. Hou et al [13] explored the influence of measurement sensor's response on the magnitude of the dynamic capillary effects at scale of a representative elementary volume (REV) and argue that the effects may be due to the experimental measurement artifacts. Their acknowledgement of the impact of the micro-heterogeneities on the dynamic capillary effects, at larger scales, is in agreement with the earlier submission of Das et al [12] and Mirzaei and Das [14].…”

“…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.…”

Dynamic capillarity during displacement process in fractured tight reservoirs with multiple fluid viscosities

“…Considering the effects of the response characteristics of the sensors, the in situ single-phase pressure is corrected according to Hou et al 5 The in situ water saturation at each time t n is calculated using the method proposed by Li et al, 39 which is more accurate for tight porous media than Archie's formula. The in situ time derivation of water saturation ( S w ∕ t) can be calculated as:…”

Geoelectrical characterization of carbonate and silicate porous media in the presence of supercritical CO2–water flow

“…This is related to the 'dynamic effect' widely reported in the P c -S relationships for many two-phase flow systems (Kalaydjian 1992;Hassanizadeh et al 2002;Camps-Roach et al 2010;Goel & O'Carroll 2011;Hou et al 2012;. It refers to the dependence of the system properties on the desaturation rate in the medium (Das et al 2007;Hou et al 2012).…”