Understanding water-oil-solid interaction by visualizing two phase flow in porous media
Water-oil-solid interactions are abundant all around us, if it’s oil extraction from rock reservoirs, remediation of solvents from the soil or just percolating coffee. In essence the coffee analogy can serve well to exemplify different interactions; making coffee with a percolator is similar to extracting oil by replacing it with water under gravitational pressure. Making an espresso is similar to the process known as fracking where water with high pressure fracture the rock formation to reach untapped oil, in both cases the oil is trapped in pores at the porous medium. We can visualize the water-oil-solid interaction by matching the refractive index of all three while suspending fluorescent beads in the oil and the water. This procedure elucidates the underlying physics using high spatial-temporal imaging of the flow in both phases.
Surfactant variations in porous media localize capillary instabilities during Haines jump
Drainage is when a wetting phase is driven out by non-wetting phase in porous media, this occurs in a series of jumps between pores known as Haines jumps but the dynamic behind it is poorly understood. We visualize the seemingly random capillary pressure pore instabilities leading to Haines jump when water replaces trapped oil in a 2d hydrophobic porous media model (Fig 1a,c). We notice that un-intuitively Haines jump occur on water-oil stagnant interfaces and not flowing interfaces where pressure instabilities should dominant. At the Haines jump we capture the dynamics of capillary pressure built up and release during the instantaneous advancement of the invading water via curvature calculations (Fig 1b,d).. The pressure built up is related to viscous drag forces between the water to a thin oil film formation which effectively extract the trapped oil. In theory the Haines jump should be spatially random in a uniform domain but they follow spatial variation of surfactant variation induced by inhomogeneous depletion.
FIG. 1: a. Trapped oil phase in 2d porous media of 50 µm3 posts array with equal distances of 75 µm, water marked by green fluorescent beads, advancement into the oil, marked by red fluorescent beads. b. The meniscus between water and oil before water advancement marked by a black line with color bar for the curvature value. c. Trapped oil phase in after water advancement into the oil. d. Meniscus between water and oil after water advancement.
Thin film formations in porous media two phase flow and their effect on Haines jumps.
Two phase flow in porous media is governed by heterogeneity, connectivity, wettability, fluid velocity and viscosity. Adding surfactant reduces the interfacial tension between the phases, lead to shear thinning, change domain wettability and can create elastic turbulence. In this study we show that drag forces induced by the surfactant effect drainage and imbibition by inducing Haines jumps through thin film formation. For that 3d porous media two phase flow experiments with suspended florescence’s beads in both phases were analyzed. This allows us to quantify the surfactant influence and the dynamic it exhibits with the porous media. We show that the trapped oil ganglia experience enhance drag from the water phase which leads to shear and extraction of oil through the thin film. This process leads to destabilization of the capillary pressure known as Haines jumps. Here, we the extant of oil thin films even on hydrophilic glass beads.
Figure 2: a.Two phase flow experiment in 3d a single 2d slice is presented in different times with oil ganglia marked in red beads. b. A PIV analysis showing the mean velocity field and direction of the oil ganglia marked by a white circle. As can be seen, there is a vortex in the stagnant oil ganglia due to interfacial drag forces, this movement is occurring well after steady state flow of water is reached. c. Thin films of mineral oil on the glass beads, marked blue by florescence dye in the oil phase. d&e. Buckling of oil ganglia under steady state water-DMSO flow for 36 houres, more than 120 pore volumes.
3D model system for fracking: fluid solid interaction during fracture advancement.
Hydraulic fracturing has dramatically increased the production of oil and gas in the US over the past decade. This increase was possible by technological advancement in the oil and gas production from tight shale rock formation. Improvement in the production process was rapid leaving many fundamental physical questions unanswered, mainly due to measurement limitations in the rock formation. As such, detailed experiments are needed to investigate how hydraulic fracturing works, specifically what influence it has on the surrounding. We will use optical microscopy techniques on indexed-matched soft model systems of oil and water filled porous media to gain insight into the fundamental physics of this process.
Figure 3: (a) Producing single emulsion polymer beads by glass capillary (b) Producing double emulsion polymer beads by PDMS device (c) Producing double emulsion polymer beads by PDMS device. (d) Single and double emulsion polymer beads, 50 µm in diameter.