Study of water-in-oil thin liquid films: Implications for the stability of petroleum emulsions

Investigation of Unresolved Interface "Rag Layer" in Athabasca Oil Sand Bitumen In Situ Recovery

Steam-assisted gravity drainage (SAGD), the leading commercial in situ bitumen recovery process, involves the underground injection of steam and produces at the well head a hot fluid containing water, hydrocarbons, and sand. This fluid is subjected to separation by diluent addition and gravity in several parallel treaters. Occasionally, the separation may be disrupted in one or few treaters by the occurrence of an unresolved interface or "rag layer" while continuing without disruption in the rest of the treaters. In the current study, we investigate "rag layer" occurrence based on the quantification of laboratory-scale and SAGD field tests and imaging of the "rag layer" morphology. The quantification results show that the formation and volume of the "rag layer" are affected by solids, mixing speed, and solvent addition. The microscopic images demonstrate the presence of both water-in-oil or oil-in water emulsions with a distinct transition between the continuous phases. The visual detection boundaries of the "rag layer" are defined as the threshold between the agglomerated and individual droplet layers. The extent of agglomeration increases in the proximity to the oil-water interface. The contribution of hydrophobic fine inorganic solids (less than 10 μm) to forming a "rag layer" is supported by their accumulation observed at the treaters' oil-water interface, compared to the feed. In well-controlled field operations, the perceived randomness of "rag layer" occurrence could be associated with the fluctuation of fine solid contents in the feed.

Soft matter dynamics: A versatile microgravity platform to study dynamics in soft matter

We describe an experiment container with light scattering and imaging diagnostics for experiments on soft matter aboard the International Space Station (ISS). The suite of measurement capabilities can be used to study different materials in exchangeable sample cell units. The currently available sample cell units and future possibilities for foams, granular media, and emulsions are presented in addition to an overview of the design and the diagnostics of the experiment container. First results from measurements performed on ground and during the commissioning aboard the ISS highlight the capabilities of the experiment container to study the different materials.

Electrohydrodynamic Instabilities in Free Emulsion Films

Electrohydrodynamic instabilities were induced in thin water-in-oil emulsion films by application of external DC electric field. The dominant wavelengths of instabilities were measured for constant electric fields of various strengths. The dominant wavelengths agreed reasonably well with theoretical predictions based on a linear stability model. The linear stability model used in this study took into account experimentally measured repulsive disjoining pressure and calculated Maxwell stress. The observation of such instabilities can help to understand the rupture mechanism of emulsion films under the influence of electric field.

Time Evolution and Effect of Dispersant on the Morphology and Viscosity of Water-In-Crude-Oil Emulsions

This study examines the time evolution and effects of adding dispersant (Corexit 9500A) at varying concentrations on the microscopic morphology and bulk viscosity of saltwater-in-crude-oil (Louisiana) mechanically mixed emulsions. Rheology is used for measuring the viscoelastic properties and viscosity, the latter at varying shear rates. Microscopy, followed by machine-learning-based analysis, is used for characterizing the size and spatial distribution of the water droplets in the emulsions. Initially, the water droplets appear as a multiscale lattice with a Sauter diameter of 5.3 μm and a polydispersity of 0.43, with small droplets aggregating around large ones. The corresponding bulk viscosity decreases with increasing shear rate from 2 orders of magnitude to 5 times higher than that of the weathered crude oil. After 7 days, the number of submicron droplets increases, the nearest-neighbor distance decreases, indicating preferential aggregation, and the viscosity increases by 56-112% at high shear rates (5-100 s^-1). After 14 and 21 days, some droplets coalesce resulting in loss of clusters and a decrease in viscosity. These trends suggest that changes in the aggregation contribute to the variations in viscosity. Subsequent analysis applies previously developed models for the effect of aggregation on the properties of the emulsion. While the reduction in viscosity is predicted by this model, matching of rates requires modification to the assumed relationship between yield stress and interdroplet forces. Adding dispersant without mixing generates Marangoni-driven flows as the water droplets coalesce. In time, part of the water separates, a fraction forms clouds of submicron droplets, and the rest remains unchanged. Mixing dispersant at low concentration with the emulsion accelerates the coalescence and phase separation. The removed water fraction increases with dispersant concentration, reaching 99.6% for a dispersant-to-emulsion concentration of 10^-3. The remaining emulsion consists of fine droplets with Newtonian viscosity that is still 4 times higher than that of the fresh crude oil but only 14% higher than that of the weathered oil.

Surface Interaction of Water-in-Oil Emulsion Droplets with Interfacially Active Asphaltenes

Adsorption of interfacially active components at the water/oil interface plays critical roles in determining the properties and behaviors of emulsion droplets. In this study, the droplet probe atomic force microscopy (AFM) technique was applied, for the first time, to quantitatively study the interaction mechanism between water-in-oil (W/O) emulsion droplets with interfacially adsorbed asphaltenes. The behaviors and stability of W/O emulsion droplets were demonstrated to be significantly influenced by the asphaltene concentration of organic solution where the emulsions were aged, aging time, force load, contact time, and solvent type. Bare water droplets could readily coalesce with each other in oil (i.e., toluene), while interfacially adsorbed asphaltenes could sterically inhibit droplet coalescence and induce interfacial adhesion during separation of the water droplets. For low asphaltene concentration cases, the adhesion increased with increasing asphaltene concentration (≤100 mg/L), but it significantly decreased at relatively high asphaltene concentration (e.g., 500 mg/L). Experiments in Heptol (i.e., mixture of toluene and heptane) showed that the addition of a poor solvent for asphaltenes (e.g., heptane) could enhance the interfacial adhesion between emulsion droplets at relatively low asphaltene concentration but could weaken the adhesion at relatively high asphaltene concentration. This work has quantified the interactions between W/O emulsion droplets with interfacially adsorbed asphaltenes, and the results provide useful implications into the stabilization mechanisms of W/O emulsions in oil production. The methodology in this work can be readily extended to other W/O emulsion systems with interfacially active components.

Interfacial Layer Properties of a Polyaromatic Compound and its Role in Stabilizing Water-in-Oil Emulsions

Physical properties of interfacial layers formed at the xylene-water interface by the adsorption of a polyaromatic organic compound, N-(1-hexylheptyl)-N'-(5-carbonylicpentyl) perylene-3,4,9,10-tetracarboxylic bisimide (in brief, C5Pe), were studied systematically. The deprotonation of the carboxylic group of C5Pe at alkaline pH made it highly interfacially active, significantly reducing the xylene-water interfacial tension. Thin liquid film experiments showed a continuous buildup of heterogeneous C5Pe interfacial layers at the xylene-water interfaces, which contributed to the formation of stable W/O emulsions. Continual accumulation and rearrangement of C5Pe aggregates at the xylene-water interface to form a thick layer was confirmed by in situ Brewster angle microscopy (BAM) and atomic force microscopy (AFM). The rheology measurement of the interfacial layer by double-wall ring interfacial rheometry under oscillatory shear showed that the interfacial layers formed from C5Pe solutions of high concentrations were substantially more elastic and rigid. The presence of elastically dominant interfacial layers of C5Pe led to the formation of stable water-in-xylene emulsions.

Interfacial sciences in unconventional petroleum production: from fundamentals to applications

With the ever increasing demand for energy to meet the needs of growth in population and improvement in the living standards, in particular in developing countries, the abundant unconventional oil reserves (about 70% of total world oil), such as heavy oil, oil/tar sands and shale oil, are playing an increasingly important role in securing global energy supply.

Role of asphaltenes in stabilizing thin liquid emulsion films

Drainage kinetics, thickness, and stability of water-in-oil thin liquid emulsion films obtained from asphaltenes, heavy oil (bitumen), and deasphalted heavy oil (maltenes) diluted in toluene are studied. The results show that asphaltenes stabilize thin organic liquid films at much lower concentrations than maltenes and bitumen. The drainage of thin organic liquid films containing asphaltenes is significantly slower than the drainage of the films containing maltenes and bitumen. The films stabilized by asphaltenes are much thicker (40-90 nm) than those stabilized by maltenes (∼10 nm). Such significant variation in the film properties points to different stabilization mechanisms of thin organic liquid films. Apparent aging effects, including gradual increase of film thickness, rigidity of oil/water interface, and formation of submicrometer size aggregates, were observed for thin organic liquid films containing asphaltenes. No aging effects were observed for films containing maltenes and bitumen in toluene. The increasing stability and lower drainage dynamics of asphaltene-containing thin liquid films are attributed to specific ability of asphaltenes to self-assemble and form 3D network in the film. The characteristic length of stable films is well beyond the size of single asphaltene molecules, nanoaggregates, or even clusters of nanoaggregates reported in the literature. Buildup of such 3D structure modifies the rheological properties of the liquid film to be non-Newtonian with yield stress (gel like). Formation of such network structure appears to be responsible for the slower drainage of thin asphaltenes in toluene liquid films. The yield stress of liquid film as small as ∼10(-2) Pa is sufficient to stop the drainage before the film reaches the critical thickness at which film rupture occurs.