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An Abstract of the Thesis Of AN ABSTRACT OF THE THESIS OF Diba Behnoudfar for the degree of Master of Science in Chemical Engineering presented on April 27, 2020. Title: Exploring the Wettability States and Contact Angle Variation in Porous Media Multi-Phase Flow Systems. Abstract approved: ______________________________________________________ Dorthe Wildenschild The wetting of a surface by a liquid is a crucial part of many natural and industrial processes. Despite numerous existing studies, some elements of wetting-dewetting such as contact angle variation are still poorly understood. Knowledge of contact angle behavior during the flow is necessary for modeling fluid displacements in capillary-dominated flows. In the context of multi-phase flow in porous medium, the lack of direct contact angle measurements inside pores (in-situ), adds to the ambiguity. This work consists of performing in-situ contact angle measurements on X-ray micro-computed tomography images of multi-phase fluid systems during quasi-static flow and investigating the effects of pore geometry and interfacial forces on contact angle. An algorithm enabled automated analysis of contact angle throughout the three-dimensional images. Observations revealed two unique contact angle variation patterns for oil (dodecane)-water and air-water systems with larger hysteresis for the oil-water. Introduction of a third phase (air) and altering surface chemistry (wettability) of a portion of solid phase, influenced oil-water contact angle near unaltered surfaces, but the overall trend remained the same. Results of this investigation show that contact angle correlates with the variations of fluid-fluid interfacial curvature and the pore radius at the wetting front. ©Copyright by Diba Behnoudfar April 27, 2020 All Rights Reserved Exploring the Wettability States and Contact Angle Variation in Porous Media Multi- Phase Flow Systems by Diba Behnoudfar A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Master of Science Presented April 27, 2020 Commencement June 2021 Master of Science thesis of Diba Behnoudfar presented on April 27, 2020 APPROVED: Major Professor, representing Chemical Engineering Head of the School of Chemical, Biological, and Environmental Engineering Dean of the Graduate School I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Diba Behnoudfar, Author ACKNOWLEDGEMENTS The author expresses sincere appreciation to Dorthe Wildenschild for her expert advice and insightful comments, Douglas Meisenheimer for his technical assistance and my family for their support. TABLE OF CONTENTS Page 1. Introduction ...................................................................................................... 1 2. Background ...................................................................................................... 3 2.1 Flow processes in porous media: drainage and imbibition ................ 3 2.1.1 Capillary pressure ..................................................................... 5 2.2 Governing equations .......................................................................... 6 2.2.1 Small capillary numbers and quasi-static regime ..................... 8 2.3 Contact angle ..................................................................................... 9 2.3.1 Contact angle hysteresis ........................................................... 10 2.3.2 Contact line pinning ................................................................. 13 2.3.3 Origins of contact angle hysteresis ........................................... 15 2.3.4 Contact angle measurement ...................................................... 17 2.4 X-ray micro-computed tomography .................................................. 19 3. Methods ........................................................................................................... 21 3.1 Fluid flow experiments ...................................................................... 21 3.2 Algorithm for contact angle measurement ........................................ 23 3.2.1 Identifying the contact points ................................................... 23 3.2.2 Creating contact line ................................................................. 23 3.2.3 Generating normal slice ............................................................ 25 3.2.4 Calculating contact angles ........................................................ 25 3.2.5 Testing of the approach ............................................................ 27 3.2.6 Limitations of the method ......................................................... 30 3.3 Image analysis ................................................................................... 30 3.3.1 Object separation ...................................................................... 30 TABLE OF CONTENTS (Continued) Page 3.3.2 Measuring curvature .................................................................. 33 3.3.3 Estimating wetted pore radius ................................................... 34 4. Results ............................................................................................................ 36 4.1. Contact angle-saturation and distribution of contact angles .......... 36 4.1.1. Air-water fluid pair ................................................................... 36 4.1.2 Oil-water fluid pair in water-wet system ................................... 36 4.1.3 Oil-water fluid pair in mixed-wet system .................................. 40 4.1.4 Overview of contact angle variation near water-wet beads ...... 42 4.2 Contact angle spatial distribution .................................................... 43 5. Discussion ...................................................................................................... 45 5.1 Conical pore model .......................................................................... 45 5.1.1 Wetted pore radius variation ..................................................... 46 5.1.2 Curvature and capillary pressure variation ................................ 49 5.1.3 Predicting the contact angle variation ....................................... 51 5.2 Effect of wettability .......................................................................... 53 6. Conclusion ...................................................................................................... 56 References .......................................................................................................... 58 LIST OF FIGURES Figure Page 1.1 Contact angle hysteresis ........................................................................... 2 2.1 2D cross-sections of a column of glass beads .......................................... 4 2.2 The stages of coalescence of pendular rings associated with a pore throat ......................................................................................................... 4 2.3 Capillary action and water rise in a glass capillary tube .......................... 5 2.4 Capillary pressure versus saturation relationship for water-oil in a pack of glass beads ............................................................................................ 6 2.5 Interface between two immiscible fluids .................................................. 7 2.6 Meniscus in a cylindrical capillary ........................................................... 8 2.7 Effect of surface roughness on apparent contact angle ............................ 10 2.8 Schematic of static and dynamic contact angle hysteresis ....................... 11 2.9 Schematic of (a) liquid column trapped in a capillary tube and (b) a raindrop .................................................................................................... 11 2.10 Critical capillary number vs viscosity ratio (M) and static contact angle 12 2.11 Contact line pinning and deformation of interface at a fixed contact point as time develops .............................................................................. 13 2.12 Photographs of a liquid bridge formed from glycerol during (a) separation and (b) approach ...................................................................... 14 2.13 (a) pendular liquid bridge (b) a schematic of the relationship between the wetting and the force hysteresis .......................................................... 14 2.14 Equilibrium states in a biconical pore segment ........................................ 16 2.15 (a) Three-phase contact line highlighted on the smoothed mesh (b) Normal vectors defined on both the oil/brine and brine/rock interfaces 18 for the contact line set ............................................................................... 2.16 Illustration of X-ray micro-CT technique with a cone-beam configuration ............................................................................................. 20 LIST OF FIGURES (Continued) Figure Page 3.1 (a) Schematic of sample holder for 3-phase flow system; in 2-phase experiments, the air ports on the sides of the column are absent (b) Schematic of entire experimental set-up ............................................... 22 3.2 Depiction of contact lines in the region of interest ............................... 24 3.3 Visualization of a 2D image obtained as a slice of a segmented image taken along the plane locally normal to the three-phase contact line 25 Representation
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