Spatio-temporally Resolved Dynamical Transitions in Flow of Pickering Emulsions through Porous Media
Creators: name: Meimanova, Aigerim S.
Publisher: name: Graduate Studies
Year: 2023
Subjects: subject: Pickering emulsion
subject: Porous media
subject: Interface interactions
subject: Conformance control
subject: Droplet plugging
subject: Engineering--Chemical

description: Complex fluids are effectively used in the oil and gas industry for conformance control, drilling, fracturing, and enhanced oil recovery. Commonly, coreflooding experiments are used to justify their potential applications. However, in many cases, the dynamics of complex fluids flow and interaction with porous media is not fully known, and the characterization techniques are too coarse to resolve interfacial activity and droplet-droplet interactions in realistic porous media. In-situ emulsion droplet formation and destabilization occurs on time scales of 0.1-1 seconds at the resolution of 1-100 μm. Such events may get unnoticed (or can only be implied) with the current computer tomography or X-Ray characterization techniques. Herein, the unique setup built by combining laser scanning confocal microscopy (LSCM) with the custom-designed micro-sandpack apparatus (thin-wall glass capillary filled with sand grains with proper fittings and pumps) is presented. The LSCM coupled micro flood apparatus permits real-time 4D (3D+time) monitoring of the fluid flow under high pressures (internal pressures up to 1,000 psi). This approach provides the direct visualization capability of traditional micromodels but with the realistic pore geometry of granular porous media. The real-time imaging of emulsion stabilized by modified cellulose nanocrystals (CNC) flow in microporous media is studied. The reduced surface charge of these nanoparticles impart inter-particle network building capabilities. These established inter-particle networks between the droplets within the bulk emulsion are responsible for the evolving yield stress of the fluid. As a result, we observe high oscillatory pressure drops that are often characterized by a dramatic increase in average pressure, which are independent of the geometric criteria of previous models of emulsion flow. Through systematic investigation of inter-droplet interactions using photonic force microscopy (PFM), we demonstrate formation of CNC chains between the droplets. Localized spatio-temporal patterns reveal a series of events (independent of CNC loading) starting from droplet deposition on the pore wall, stratification of nanoparticles from the droplet surface, droplet coalescence leading to droplet straining in pore constrictions, and consequent emulsion droplet jamming. These jammed structures flush upon yielding and jam again in the new pore constriction in a cyclical manner. We then explain that highly oscillatory pressures result from: i) strong attractive interactions between droplets in contact and ii) mechanical connections that persist between separated droplets. We demonstrate that these CNC chains are a prerequisite for the formation of stratified nanoparticle layers within a single pore and the effective permeability reduction of porous media. This approach (temporal and spatial resolution in realistic geometry) is an important advance of complex fluid flow behaviour and is a valuable complement to traditional larger-scale coreflooding experiments.