Speaker
Description
Emulsions flow in porous media has been found to play an important role in hydrocarbon recovery, especially in enhanced oil recovery (EOR) for conformance control in shale oil recovery where mixed oil and water flow through fractures. However, the mechanisms ruling emulsions flow remain elusive with studies mostly limited to empirical correlations. Recent development of microfluidic technologies allows direct visualization of fluid behaviors at pore-scale, but most studies of emulsions flow using microfluidic chips focus on straight channels or the behaviors of single droplets. In order to reveal the underlying mechanisms of emulsion flow in porous media, it is still required to study a more realistic scenario: the flow of sequential droplets in a flow channel with varying aperture.
We conduct emulsion flow experiments in a 3D printed transparent model that integrates an emulsion generator and a main flow channel. The emulsion generator consists of a T-junction to generate droplets of monodispersed size while to control dispersed phase flow rate, and a second T-junction downstream to regulate the continuous phase flow, which allows us to independently control three variables of emulsion flow: dispersed phase injection rate (Qd), droplet size (d), and total emulsion flow rate (Q). Downstream of the emulsion generator is the main flow channel, which consists of 100 ‘pore-throat’ microstructures where the ‘pore’ and ‘throat’ are the maximum (0.8 mm) and minimum (0.2 mm) of fractures aperture. The pressure drop (ΔP) along the main flow channel is monitored.
Two regimes of emulsion flow through the fracture with varying aperture is identified. At low capillary number (Ca), capillary pressure dominates and Darcy’s law completely fails. ΔP is determined by the number of droplets retaining in the main channel. At large Ca, viscous effects dominate over the capillary effects, and ΔP approximates the value predicted by Darcy’s law. As a consequence, many counter-intuitive behaviors are observed. For example, when Qd and d are fixed, ΔP becomes a non-monotonic function of Q. Specifically, when Q is very small, the system is in capillary regime, and ΔP decreases with increasing Q, because the number of droplets retaining in the main flow channel decreases. However, when Q is very high, the system is in viscous regime, and ΔP increases with increasing Q following Darcy’s law.
We further establish a physics-based correlation to functionalize the pressure difference (ΔP) and thus the apparent viscosity by the three independent variables (Qd, d, and Q). A phase diagram is summarized to demonstrate the transition between capillary regime and viscous regime. This work initiated a novel framework towards comprehensive understanding of emulsions flow in porous media.
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