Mechanisms controlling fluid breakup and reconnection during two-phase flow in porous media

The use of Darcy's law to describe steady-state multiphase flow in porous media has been justified by the assumption that the fluids flow in continuously connected pathways. However, a range of complex interface dynamics have been observed during macroscopically steady-state flow, including intermittent pathway flow where flow pathways periodically disconnect and reconnect. The physical mechanisms controlling this behavior have remained unclear, leading to uncertainty concerning the occurrence of the different flow regimes. We observe that the fraction of intermittent flow pathways is dependent on the capillary number and viscosity ratio. We propose a phase diagram within this parameter space to quantify the degree of intermittent flow.

Figure 1

Capillary numbers and viscosity ratios explored in this research (color), compared to observations from the literature for a sandstone (black) [4, 14, 15, 17].

Figure 2

(a) Grayscale data taken during the coinjection of nitrogen and brine for the $f_w=0.5$ high Ca nitrogen scan, (b) segmentation of the intermediate grayscale shown in blue for the same scan as (a), and (c) segmentation of the intermittent phase shown in blue for the same scan as (a). Flow is out of the page.

Figure 3

Viscosity ratio against the capillary number for the total flow, color coded to the amount of intermittency identified in the system. The percent intermittency is the percentage volume of the pore space identified as containing an intermittent pathway during a scan.

Figure 4

Phase diagram for steady-state two-phase flow with average experimental results plotted. White areas denote transition zones between the different steady-state flow regimes, although it should be noted that these boundaries are speculative and require further research to be quantified. Red dashed boxes denote the areas relevant to certain subsurface scenarios, highlighting the importance of this work to environmental and industrial applications, with typically capillary numbers taken from [5], viscosity ratios for gaseous systems from [29], viscosity ratios for oils from [30], and the impact of polymer flooding from [31, 32].