Structure and Rheology of Monodisperse and Bimodal Emulsions

<p>Emulsions are the basis for many commercial products such as foodstuffs and paint due in part to their highly tunable flow properties. It is qualitatively understood that factors such as the dispersed phase droplet size and size distribution should affect how an emulsion flows because they influence how droplets can deform or pack. Since standard emulsification techniques such as blending and homogenization cannot produce emulsions with well-defined size distributions, little work has been done to, in particular, quantitatively determine the influence of droplet size distribution on emulsion flow properties. Consequently, in this investigation we have probed how the droplet size distribution affects emulsion flow properties by using model monodisperse emulsion systems with narrow, controllable droplet size distributions. Using a microfluidic flow focusing device, dodecane-in-water emulsions with diameters between 50 to 100 m with polydispersities less than 5% were produced, as characterized by pulsed field gradient nuclear magnetic resonance and optical microscopy. Due to the relatively large size of the droplets, it was only possible to examine the creamed phase of the emulsion. Samples of known polydispersity were made by mixing known quantities of two monodisperse emulsions. The monodisperse and bimodal emulsions were then subjected to rotational and oscillatory shear flow using a controlled stress rheometer to determine the effects of droplet size and size distribution on emulsion flow properties. Rotational and oscillatory rheological experiments showed that the monodisperse emulsions had two distinct behaviours: foam-like with appreciable thixotropy and yield stresses as well as emulsion-like with no evident thixotropy. The transition between these two behaviours appears to happen at a critical droplet radius between 33 and 37 micrometres. The rheological properties of the bimodal emulsions was split into three distinct behaviours. In samples that could be considered a matrix of large droplets perturbed by smaller droplets, the flow properties were similar to those of the constituent emulsion with the larger droplets. Increasing the number fraction of smaller droplets to a 1:1 ratio creates an entirely new phase with significantly reduced elastic properties. Surprisingly, when the emulsion primarily consists of small droplets, the flow properties are most similar to that of the large droplets. Additionally, despite the microstructural differences, all emulsions showed flow characteristics typical of soft glassy materials above the glass transition temperature. These results demonstrate the significant influence of microstructure on emulsion rheology, where altering the droplet size or polydispersity essentially creates a new phase with its own unique flow properties that is not simply a combination of the properties of the individual monodisperse components that make up the sample</p>

Structure and Rheology of Monodisperse and Bimodal Emulsions

<p>Emulsions are the basis for many commercial products such as foodstuffs and paint due in part to their highly tunable flow properties. It is qualitatively understood that factors such as the dispersed phase droplet size and size distribution should affect how an emulsion flows because they influence how droplets can deform or pack. Since standard emulsification techniques such as blending and homogenization cannot produce emulsions with well-defined size distributions, little work has been done to, in particular, quantitatively determine the influence of droplet size distribution on emulsion flow properties. Consequently, in this investigation we have probed how the droplet size distribution affects emulsion flow properties by using model monodisperse emulsion systems with narrow, controllable droplet size distributions. Using a microfluidic flow focusing device, dodecane-in-water emulsions with diameters between 50 to 100 m with polydispersities less than 5% were produced, as characterized by pulsed field gradient nuclear magnetic resonance and optical microscopy. Due to the relatively large size of the droplets, it was only possible to examine the creamed phase of the emulsion. Samples of known polydispersity were made by mixing known quantities of two monodisperse emulsions. The monodisperse and bimodal emulsions were then subjected to rotational and oscillatory shear flow using a controlled stress rheometer to determine the effects of droplet size and size distribution on emulsion flow properties. Rotational and oscillatory rheological experiments showed that the monodisperse emulsions had two distinct behaviours: foam-like with appreciable thixotropy and yield stresses as well as emulsion-like with no evident thixotropy. The transition between these two behaviours appears to happen at a critical droplet radius between 33 and 37 micrometres. The rheological properties of the bimodal emulsions was split into three distinct behaviours. In samples that could be considered a matrix of large droplets perturbed by smaller droplets, the flow properties were similar to those of the constituent emulsion with the larger droplets. Increasing the number fraction of smaller droplets to a 1:1 ratio creates an entirely new phase with significantly reduced elastic properties. Surprisingly, when the emulsion primarily consists of small droplets, the flow properties are most similar to that of the large droplets. Additionally, despite the microstructural differences, all emulsions showed flow characteristics typical of soft glassy materials above the glass transition temperature. These results demonstrate the significant influence of microstructure on emulsion rheology, where altering the droplet size or polydispersity essentially creates a new phase with its own unique flow properties that is not simply a combination of the properties of the individual monodisperse components that make up the sample</p>

An Improved Study of Emulsion Flooding for Conformance Control in a Heterogeneous 2D Model with Lean Zones

Summary Use of oil-in-water (O/W) emulsion has shown its potential for conformance control in heterogeneous porous media, yet it is essential to understand how to improve the conformance control performance in the heterogeneous 2D model with lean zones before it is applied in the fields. In this paper, an O/W emulsion-based conformance control method is improved through newly designed flow tests and optimized modeling study. A heterogeneous 2D model was designed with a high water mobility zone (HWMZ) and a low water mobility zone (LWMZ) separated by a horizontal injection well to mimic real oil sands with lean zones (top- or bottomwater) and with application of horizontal wells. Optimal conformance control strategies were proposed and examined in the 2D model by injecting correspondingly designed O/W emulsions. In an improvement of our previously proposed emulsion flow model (Ding et al. 2020c), we introduce the real phenomena of permeability reduction (PR) coefficients in this paper to describe the three ambiguous coefficients: flow distribution coefficient (γ), plugging coefficient (α), and retention rate coefficient (a). This newly developed model can incorporate with characteristics of the emulsion and the heterogeneous porous media through the introduction of the experimentally derived PR coefficient. It is well established in COMSOL Multiphysics® (COMSOL AB 2005), and the modeling results show good agreement with the experimentally monitored results in the three types of flow tests. This work bridges experimental and mathematical studies on emulsion flow in 2D models associated with lean zones and is able to provide a guide on optimal emulsion design and injection strategy for optimal conformance control performances.

Flow behaviour of water-in-oil emulsions stabilized by wax crystals

The large temperature gradients experienced by crude oil emulsions in pipelines found in colder environments can lead to the precipitation, deposition and build-up of wax-like species from the crude oil onto the pipe wall that result in flow assurance problems. The objective of this thesis was to understand the rheological behaviour of model water-in-oil emulsions stabilized by wax crystals. The microstructure, phase transitions and rheology of model emulsions constisting of water, mineral oil, parrafin wax and the emulsifier polyglycerol polyricinoleate (PgPr) were investigated. Changes in emulsion flow begaviour (steady state and dynamic) as a function of composition, termperature and passage through a laboratory-scale flowloop were investigated, with these parameters significantly affecting shear flow, yield stress and viscoelasticity. The gelation temperature of wax-containing ('waxy') oil was slightly lower than that of its equivalent emulsion due to differences in the structure of the gelled emulsion network. Overall, this study successfully showed that there exist significant differences in the microstructure and flow behaviour of model crude oil emulsions when wax and a dispersed aqueous phase are present.

Flow behaviour of water-in-oil emulsions stabilized by wax crystals

The large temperature gradients experienced by crude oil emulsions in pipelines found in colder environments can lead to the precipitation, deposition and build-up of wax-like species from the crude oil onto the pipe wall that result in flow assurance problems. The objective of this thesis was to understand the rheological behaviour of model water-in-oil emulsions stabilized by wax crystals. The microstructure, phase transitions and rheology of model emulsions constisting of water, mineral oil, parrafin wax and the emulsifier polyglycerol polyricinoleate (PgPr) were investigated. Changes in emulsion flow begaviour (steady state and dynamic) as a function of composition, termperature and passage through a laboratory-scale flowloop were investigated, with these parameters significantly affecting shear flow, yield stress and viscoelasticity. The gelation temperature of wax-containing ('waxy') oil was slightly lower than that of its equivalent emulsion due to differences in the structure of the gelled emulsion network. Overall, this study successfully showed that there exist significant differences in the microstructure and flow behaviour of model crude oil emulsions when wax and a dispersed aqueous phase are present.

A New Mechanistic Model for Emulsion Rheology and Boosting Pressure Prediction in Electrical Submersible Pumps (ESPs) under Oil-Water Two-Phase Flow

Summary As the second most widely used artificial lift method in the petroleum industry, electrical submersible pumps (ESPs) maintain or increase flow rates by converting the kinetic energy to hydraulic pressure. As oilfields age, water is invariably produced with crude oil. The increase of water cut generates oil-water emulsions due to the high-shearing effects inside a rotating ESP. Emulsions can be stabilized by natural surfactants or fine solids existing in the reservoir fluids. The formation of emulsions during oil production creates a high viscous mixture, resulting in costly problems and flow assurance issues, such as increasing pressure drop and reducing production rates. This paper, for the first time, proposes a new rheology model to predict the oil-water emulsion effective viscosities and establishes a link of fluid rheology and its effect with the stage pressure increment of ESPs. Based on Brinkman's (1952) correlation, a new rheology model, accounting for ESP rotational speed, stage number, fluid properties, and so on, is developed, which can also predict the phase inversion in oil-water emulsions. For the new mechanistic model to calculate ESP boosting pressure, a conceptual best-match flow rate (QBM) is introduced. QBM corresponds to the flow rate whose direction at the ESP impeller outlet matches the designed flow direction. Induced by the liquid flow rates changing, various pressure losses can be derived from QBM, including recirculation losses, and losses due to friction, leakage, sudden change of flow directions, and so on. Incorporating the new rheology model into the mechanistic model, the ESP boosting pressure under oil-water emulsion flow can be calculated. To validate the proposed model, the experimental data from two different types of ESPs were compared with the model predictions in terms of ESP boosting pressure. Under both high-viscositysingle-phase fluid flow and oil-water emulsion flow, the model predicted ESP pressure increment matches the experimental measurements well. From medium to high flow rates with varying oil viscosities and water cuts, the prediction error is less than 15%.