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Pore-scale Study of Surface Characteristics (Roughness and Heterogeneity) and Fluid Properties on Wettability and Dynamics of Two-phase Flow in Porous Media

Shirazi, Mahsa | 2025

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58480 (06)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Masihi, Mohsen; Mahani, Hassan; Tamsilian, Yousef
  7. Abstract:
  8. The interaction between fluids and solid surfaces has long been recognized as a key factor influencing flow behavior in porous media. Despite its significance, the impact of surface roughness and heterogeneity on this interaction has received relatively limited attention, presenting substantial challenges in accurately analyzing fluid dynamics and underscoring the need for fundamental research. This study aims to comprehensively investigate the combined effects of surface roughness, heterogeneity, and fluid properties on flow behavior at both micro and macro scales, and has been conducted in four distinct phases. In the first phase, various surface roughening techniques—including laser engraving, cream etching, a combination of laser and cream etching, and hydrofluoric acid etching—were evaluated through detailed characterization analyses. The influence of temperature on surface chemistry, topology, roughness, and depth was also examined. The second phase involved both ex-situ and in-situ contact angle measurements. In the third phase, displacement experiments (drainage and imbibition) were performed using micromodels with varying degrees of surface roughness and heterogeneity over a wide range of capillary numbers (10⁻⁷ to 10⁻⁴) and viscosity ratios (0.1 to 10). The fourth phase introduced modified Lenormand diagrams to classify two-phase flow regimes under diverse surface roughness and heterogeneity conditions. Findings from the first phase suggested that laser engraving and hydrofluoric acid etching are the most effective methods for producing controlled roughness with either homogeneous or heterogeneous distributions. Notably, elevated temperatures did not alter surface chemistry across all methods; however, cream etching failed to maintain surface roughness at higher temperatures, rendering it unsuitable for generating surface roughness. Consequently, three micromodels with heterogeneous roughness distributions—low (5 μm), medium (13 μm), and high (21 μm)—were fabricated via hydrofluoric acid exposure for 5, 7.5, and 10 minutes, respectively. An additional homogeneous high-roughness (21 μm) micromodel was created using laser engraving. Contact angle experiments from the second phase demonstrated that increased roughness enhances wettability by expanding the contact area of the wetting fluid, leading to stronger hydrophilicity and greater contact angle hysteresis—up to 3 degrees in highly rough surfaces. It was also observed that the pinning of the fluid-fluid interface, caused by sharp local roughnesses, could impede the advance of the invading phase and increase local contact angles. Classical models such as Wenzel’s proved inadequate in capturing these effects, prompting the development of a new model that incorporates interface pinning and a modified roughness parameter to more accurately predict contact angle behavior. In the third phase, displacement tests revealed that the influence of roughness and heterogeneity on drainage and imbibition is governed by dominant forces, wettability conditions, pore-scale flow dynamics, and fluid properties. These effects were particularly pronounced at low capillary numbers (below 10⁻⁶). Surface heterogeneity led to irregular flow patterns, mixed-wettability behaviors, and fluid bypassing. During drainage, at low capillary numbers, roughness amplified capillary pressure barriers and destabilized the flow front, reducing recovery of the wetting phase. Conversely, interface pinning helped stabilize the front and enhance recovery by delaying fluid invasion. At higher capillary numbers (above 10⁻⁶), the flow became more stable and less sensitive to surface conditions. In imbibition processes under low capillary numbers, roughness facilitated the penetration of the wetting phase and formation of thin films, aiding entry into smaller pores. However, roughness heterogeneities caused front instabilities and fluid trapping. At higher capillary numbers, roughness helped break up residual oil ganglia, improving recovery efficiency. Finally, the fourth phase showed that surface roughness and heterogeneity could shift flow regime boundaries in Lenormand diagrams by influencing capillary forces. These effects included expanding stable displacement zones through front stabilization, limiting viscous fingering by increasing frictional resistance, and extending capillary fingering regimes—particularly at low capillary numbers—by strengthening capillary forces. The significant insights gained from this research advance the understanding of fluid flow behavior in porous media and provide valuable scientific and practical implications for enhanced oil recovery and subsurface transport processes
  9. Keywords:
  10. Surface Roughness and Heterogeneity ; Mixed Wettability ; Two-Phase Flow Modeling ; Flow Regime ; Surface Heterogeneity (Roughness) ; Lenormand Diagram

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