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• Brodin, Joachim Falck; Pierce, James Kevin; Reis, Paula Kozlowski Pitombeira; Rikvold, Per Arne; Moura, Marcel & Jankov, Mihailo [Show all 7 contributors for this article] (2025). Interface instability of two-phase flow in a three-dimensional porous medium. Physical Review Fluids. 10(6). doi: 10.1103/hm82-167x. Full text in Research Archive Show summary

  We present an experimental study of immiscible, two-phase fluid flow through a three-dimensional porous medium consisting of randomly packed, monodisperse glass spheres. Our experiments combine refractive-index matching and laser-induced fluorescence imaging to resolve the morphology and stability of the moving interface resulting from the injection of one fluid into another. The imposed injection rate sets a balance between gravitational and viscous forces, producing interface morphologies which range from unstable collections of tangled fingers at low rates to stable sheets at high rates. The image data are complemented by time-resolved pressure measurements. We develop a stability criterion for the fluid interface based on the analysis of the 3D images and the pressure data. This criterion involves the Darcy permeability in each of the two phases and the time derivative of the pressure drop across the medium. We observe that the relative permeability encountered by the invading fluid is modified by the imposed flow rate in our experiment, which impacts the two-phase flow dynamics. We show that, in addition to the balance between the relevant forces driving the dynamics, local regions of crystalline order in the beadpack (crystallites) affect the stability of the invading front. This work provides insights into how disorder on multiple length scales in porous media can interact with viscous, capillary, and gravitational forces to determine the stability and dynamics of immiscible fluid interfaces.

• Brodin, Joachim Falck; Måløy, Knut Jørgen; Moura, Marcel & Rikvold, Per Arne (2023). Rising Invader. In Médici, Ezequiel F. & Otero, Alejandro D. (Ed.), Album of Porous Media. Springer. ISSN 9783031238000. p. 55–55. doi: 10.1007/978-3-031-23800-0_41. Full text in Research Archive
• Brodin, Joachim Falck; Rikvold, Per Arne; Moura, Marcel & Måløy, Knut Jørgen (2023). Invasion Pattern. In Médici, Ezequiel F. & Otero, Alejandro D. (Ed.), Album of Porous Media. Springer. ISSN 9783031238000. p. 59–59. doi: 10.1007/978-3-031-23800-0_45. Full text in Research Archive
• Brodin, Joachim Falck; Moura, Marcel; Toussaint, Renaud; Måløy, Knut Jørgen & Rikvold, Per Arne (2022). Visualization by optical fluorescence of two-phase flow in a three-dimensional porous medium. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 2241. doi: 10.1088/1742-6596/2241/1/012004. Full text in Research Archive Show summary

  Abstract Slow flow of a single fluid through a porous medium is well understood on a macroscopic level through Darcy’s law, a linear relation between flow rate and a combination of pressure differences, viscosity, and gravitational forces. Two-phase flow is complicated by the interface separating the fluids, but understanding of two-dimensional, two-phase flow has been obtained from experiments using transparent cells. In most three-dimensional media, however, visual observation is difficult. Here, we present preliminary results of experiments on a model medium consisting of randomly packed glass spheres, in which one fluorescent liquid invades another. By refractive index matching and scanning with a sheet-shaped laser beam, we obtain slices of the flow patterns, which we combine into three-dimensional pictures. We observe a compact region of invading fluid, surrounded by finger-like protrusions. The compact region becomes more dominant with increasing invader flow rate. The patterns are theoretically analyzed in terms of the interplay between gravitational, viscous, and capillary forces.

• Brodin, Joachim Falck; Rikvold, Per Arne; Moura, Marcel; Toussaint, Renaud & Måløy, Knut Jørgen (2022). Competing Gravitational and Viscous Effects in 3D Two-Phase Flow Investigated With a Table-Top Optical Scanner. Frontiers in Physics. 10. doi: 10.3389/fphy.2022.936915. Full text in Research Archive Show summary

  We present experiments and theory describing the transition from viscosity-stabilized flow to gravitationally unstable fingering for two-phase flow in a cubic box, filled with a synthetic porous medium. Observation is made possible by the use of our newly developed table-top 3D scanner based on optical index matching and laser-induced fluorescence, which is described in detail. In the experiment, a more dense, more viscous fluid injected at a fixed flow rate from a point source at the top of the flow cell displaces a less viscous, less dense fluid. We observe a stable invasion zone near the inlet, which increases in size with increasing flow rates, and presents initially a close to hemispherical shape. At later times, the invasion front transits to an unstable mode and a fingering flow regime. The transition occurs at a predicted critical radius, Rc, corresponding to the zero of the combined viscous and gravitational pressure gradient.

• Flekkøy, Eirik Grude & Brodin, Joachim Falck (2022). Discerning between Different 'Oumuamua Models by Optical and Infrared Observations. Astrophysical Journal Letters. ISSN 2041-8205. 925(2). doi: 10.3847/2041-8213/ac4b62. Full text in Research Archive Show summary

  Abstract The first interstellar object to be observed in our solar system, 1I/2017 U1 ’Oumuamua, combines the lack of observable cometary activity with an extra-gravitational acceleration. This has given rise to several mutually exclusive explanations based on different assumptions in the material composition of ’Oumuamua. We show how a combination of observations in the infrared and optical spectra may serve to distinguish between these explanations once another object with ’Omuamua-like properties comes close enough to Earth. This possibility is linked to the widely different thermal properties of the different material models that have been proposed. Developing a model for the thermal conduction and infrared signal from a fractal model, we compare predictions of the infrared signal with that from standard thermal models that assume ’Oumuamua to be either a solid piece of rock/ice or a thin sheet.

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• Moura, Marcel; Brodin, Joachim Falck; Reis, Paula Kozlowski Pitombeira; Pierce, Kevin; Jankov, Mihailo & Rikvold, Per Arne [Show all 11 contributors for this article] (2026). From Thin Films to Stable Fronts: Tabletop Experimental Approaches to 2D and 3D Porous Media Flows. doi: https:/www.youtube.com/live/bSQ-sHK6FTU?si=W9_rbJ5BkyRPHP0m. Full text in Research Archive
• Brodin, Joachim Falck; Moura, Marcel; Pierce, James Kevin; Reis, Paula Kozlowski Pitombeira; Rikvold, Per Arne & Jankov, Mihailo [Show all 7 contributors for this article] (2025). Experimental Investigation of Two-Phase Flow with a Table-Top Optical Scanner: Interface Instability in a Three-Dimensional Porous Medium. Full text in Research Archive
• Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude; Brodin, Joachim Falck; Reis, Paula Kozlowski Pitombeira & Linga, Gaute [Show all 7 contributors for this article] (2024). A pool of two-phase flows experiments: films, bursts, patterns and avalanches. Full text in Research Archive
• Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude; Brodin, Joachim Falck; Reis, Paula Kozlowski Pitombeira & Linga, Gaute [Show all 7 contributors for this article] (2024). A little bit of our activity at PoreLab and Njord. Full text in Research Archive
• Brodin, Joachim Falck; Rikvold, Per Arne; Moura, Marcel; Pierce, James Kevin; Toussaint, Renaud & Måløy, Knut Jørgen (2023). Experimental investigation of two phase flow with a table top optical scanner: the competition between viscous and gravitational effects under different boundary conditions. Full text in Research Archive
• Moura, Marcel; Brodin, Joachim Falck; Måløy, Knut Jørgen; Rikvold, Per Arne; Flekkøy, Eirik Grude & Jankov, Mihailo [Show all 8 contributors for this article] (2022). Thin film flow: fluid transport and pollution spreading in porous media. Full text in Research Archive
• Moura, Marcel; Brodin, Joachim Falck; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Rikvold, Per Arne (2022). Capillary pumping – the spreading of pollution in porous media. Full text in Research Archive
• Måløy, Knut Jørgen; Brodin, Joachim Falck; Rikvold, Per Arne; Moura, Marcel; Toussaint, Renaud & Schaefer, Gerhard [Show all 7 contributors for this article] (2020). Drainage in porous media under influence of a gravitational field. Full text in Research Archive
• Rikvold, Per Arne; Brodin, Joachim Falck; Moura, Marcel Nascimento de & Måløy, Knut Jørgen (2020). Visualization of Two-phase Flow in a Three-dimensional Porous Medium. Full text in Research Archive
• Rikvold, Per Arne; Brodin, Joachim Falck; Moura, Marcel Nascimento de & Måløy, Knut Jørgen (2020). Visualization of Two-phase Flow in a Three-dimensional Porous Medium. Full text in Research Archive
• Brodin, Joachim Falck; Måløy, Knut Jørgen; Moura, Marcel; Toussaint, Renaud & Rikvold, Per Arne (2020). An experimental study of the interplay between viscous, capillary and gravitational forces in two-phase flow in a three-dimensional porous medium. Full text in Research Archive Show summary

  We study the interplay between viscous, capillary and gravitational forces in two-phase flow in a threedimensional porous medium, with the use of an optical scanner based on index-matched medium and fluorescent fluids. A more viscous, denser, fluid is injected into a less viscous, less dense fluid in a 3D porous medium, comprised of randomly packed glass beads of uniform size. We tune the injection rate over 10 experiments. Experience from the 2D scenario suggests that with a slow injection rate capillary and gravitational forces will dominate, and we should observe an unstable displacement and fingering. Conversely, with a high injection rate, viscous forces will dominate, leading to a more stable displacement and a narrower invasion front. How do the 2D findings hold up in the 3D scenario? We confirm the qualitative findings from the 2D experiments and establish a clear regime change, from unstable to stable displacement. We seek to derive a dimensionless number to quantify the relevant balance of forces and consider this number in relation to the invasion pattern. We characterize the invasion by Minkowski-functionals and fractal dimensions and seek relations between the found geometries and the derived dimensionless numbers.

• Brodin, Joachim Falck; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Moura, Marcel Nascimento de (2025). Stable and unstable invasion in two-phase flow in three-dimensional porous media. Universitetet i Oslo. Full text in Research Archive Show summary

  The thesis centers on three research papers [1–3], investigating the dynamics of two-phase flow in porous media using an custum built optical 3D scanner in lab experiments. We study cases where a more viscous, denser fluid is injected into a less viscous, lighter fluid from above at constant flow rates. The focus is on the transition from stabilized invasion at high flow rates to instability at lower rates, with emphasis on dynamics and structure near the transition. The first two papers examine injection from a single point source near the top of the invasion cell. Initially, the invading fluid expands spherically, occupying adjacent pores. High local velocity ensures that capillary pressure overcomes pore-throat thresholds, even in narrow passages. The front area grows as it advances and the local flow velocity at the front decreases, reducing capillary pressure. Downward protrusions gain additional capillary pressure from the hydrostatic column, favoring penetration in these regions. When the local flow rate is sufficiently low, the hydrostatic pressure build up in the protrusions is larger than the loss of viscous pressure as compared to the lagging front. At this stage, the invasion body transitions from a compact sphere to downward-extending branches, in what we label fingering. We derive a theoretical prediction for a flow-rate-dependent critical radius for this transition and compare it with experiments, finding good agreement. In the third paper, we modify the experiment to initiate invasion as a horizontal sheet, spanning the cross section of the cell. We analyze the transition to instability as a function of flow rate. A stability criterion for the fluid interface is developed based on pressure data, incorporating flow-velocity dependent two-phase permeability and the time derivative of the pressure drop. We observe that the invading fluid’s relative permeability varies with flow rate. We measure the effects of heterogeneities in the porous media caused by regions of crystalline structures with low local permeability. We label this effect pinning and derive a methodology to measure how the front geometry can be decomposed as a sum of fingering and pinning. Together, the work elucidates how multiscale disorder in porous media interacts with viscous, capillary, and gravitational forces to shape immiscible fluid interface stability and dynamics.

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