Effects of flow history on oil entrapment in porous media: An experimental study

Abstract

The effect of flow history on fluid phase entrapment during immiscible two-phase flow in Hele-Shaw cells packed with spherical and crushed glass beads is investigated. The wetting fluid is injected into an initially oil saturated cell at a welldefined capillary number. It is observed that the size and shape of the trapped clusters strongly depend on the history of flooding such that less oil was trapped in the medium when the injecting capillary number gradually increased to the final maximum capillary number compared to the case when the injection was started and maintained constant at the maximum capillary number. In addition, a comprehensive series of experiments were conducted to delineate the effects of the capillary number on the phase entrapment. Contrary to previously published data, our experimental data reveal that the residual oil saturation depends on capillary number nonmonotonically. A physically based relationship to scale the capillary desaturation curve is proposed.

Experimental study on nonmonotonicity of Capillary Desaturation Curves in a 2‐D pore network

“…Recently, a nonmonotonic relationship between the Ca and residual oil saturation was proposed describing the experimental data measured during imbibition experiments (water displacing oil in a Hele-Shaw cell packed with glass beads) [Khosravian et al, 2014]. To describe the measured CDC, equation (1) was proposed which is used in the present analysis expressed as:…”

“…Also, the fact that the residual oil saturation at low capillary numbers is larger in the case of M = 1.00 compared to unfavorable viscosity ratios, is consistent with the pore doublet model which suggests that the phase entrapment in the large pores might become less as M decreases [ Abrams , ]. Moreover, from Figure a, it can be deduced that in the cases of M = 0.01 and M = 0.08, the value of Ca corresponding to the maximum of S ro lies in the interval of 10 −4 −10 −5 , which is in good agreement with the values reported in other papers [ Dias and Payatakes , ; Chatzis et al ., ; Khosravian et al ., ; Gioia and Urciuolo , ].…”

“…Recently, a nonmonotonic relationship between the Ca and residual oil saturation was proposed describing the experimental data measured during imbibition experiments (water displacing oil in a Hele‐Shaw cell packed with glass beads) [ Khosravian et al ., ]. To describe the measured CDC, equation (1) was proposed which is used in the present analysis expressed as: where and indicate the maximum trapped phase saturation and the critical capillary number where the maximum trapped phase saturation occurs, respectively, and a is a fitting parameter.…”

“…It has to be noted that equation (1) was developed under the assumption of negligible capillary fingering, which was the case in the experiments reported by Khosravian et al . []. However, capillary fingering is actually present in some of our experiments and such an assumption may be valid only for M = 0.01 (i.e., the most viscous oil).…”

“…An interesting observation is that the obtained value for in our study (3.3 × 10 −5 ) is very close to the range of 4.3 × 10 −5 −5.6 × 10 −5 obtained by Khosravian et al . [].…”