Disconnection flow-mediated grain rotation Qiu, Caihao; Salvalaglio, Marco; Srolovitz, David J ...
Proceedings of the National Academy of Sciences - PNAS,
01/2024, Letnik:
121, Številka:
1
Journal Article
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Grain rotation is commonly observed during the evolution of microstructures in polycrystalline materials of different kinds, including metals, ceramics, and colloidal crystals. It is widely accepted ...that interface migration in these systems is mediated by the motion of line defects with step and dislocation character, i.e., disconnections. We propose a crystallography-respecting continuum model for arbitrarily curved grain boundaries or heterophase interfaces, accounting for the disconnections' role in grain rotation. Numerical simulations demonstrate that changes in grain orientations, as well as interface morphology and internal stress field, are associated with disconnection flow. Our predictions agree with molecular dynamics simulation results for pure capillarity-driven evolution of grain boundaries and are interpreted through an extended Cahn-Taylor model.
•Visualization of displacement patterns of immiscible flow.•Phase diagram for three-dimensional porous media.•Characterization of invading fluid morphology.•Invasion dynamics for typical capillary ...and viscous fingering.
The immiscible fluid displacement pattern, controlled by the balance of viscous and capillary forces has a significant effect on the recovery or storage efficiency in subsurface processes. The phase diagram of displacement patterns has been extensively studied for the two-dimensional (2D) micromodel; however, that of the three-dimensional (3D) porous media has received little attention. This work experimentally studied the immiscible drainage displacement in an unconsolidated packed bed at the pore scale with a wide range of capillary number Ca and viscosity ratio M using X-ray micro-tomography. Three typical displacement patterns, namely viscous fingering, capillary fingering, and stable displacement, were observed in 3D porous media. The rough location of three displacement patterns on the Ca–M diagram was consistent with previous studies in 2D micromodel. The boundaries for three regimes were determined based on the quantitative analyses of the saturation distribution as functions of Ca and M. Compared with the result in 2D micromodel, a broader transition zone between different regimes was found in 3D porous media. The characterizations of finger structures (e.g. fractal dimension and finger width) were applied to reveal the mechanism of how the injected fluid invades the pores and throats inside porous media for different displacement patterns. The average fractal dimension of capillary fingerings was 2.58 ± 0.05, which agrees with the 2.55 defined by the invasion percolation theory. For the viscous fingering, where the viscous force dominates the invasion process, the invading fluid follows a several preferential flow paths in the same direction as the injection and the finger width was only 1 to 2 pore bodies. Besides, the invasion dynamics under continuous injection conditions were compared for typical viscous and capillary fingerings. This study may improve our understanding of the dynamics of displacement processes jointly governed by the viscous/capillary forces in 3D porous media. Furthermore, the phase diagram under various conditions (i.e. a wide range of Ca and M) can help to find a suitable reservoir conditions for subsurface processes.
•Impact of imbibition-profile shape on wettability is investigated thermodynamically.•Wettability is related to change in Helmholtz free energy during spontaneous imbibition process.•Helmholtz free ...energy is related to area under the curve and slope of imbibition profile.•A modified Lucas-Washburn equation is proposed for co-current imbibition process.•A wettability index is proposed using the calculated Helmholtz free energy values.
Spontaneous imbibition profiles are widely used for wettability evaluation of porous media such as rocks. However, mostly the equilibrium imbibed volume is the basis for wettability evaluation. Here, we model the relationship between the shape of imbibition profile and wettability of a medium. We develop a wettability evaluation criterion based on the change in Helmholtz free energy of the system during the imbibition process. The model relates the Helmholtz free energy to the area under the profile, the slope of the imbibition profile, equilibrium imbibed volume, and equilibrium time. We propose a modified form of Lucas-Washburn equation to model the capillary-driven flow of a viscous wetting phase into a porous medium saturated with a viscous non-wetting phase. We introduce a wettability index using the volume-normalized Helmholtz free energy. Finally, the model is tested on imbibition data of eight twin rock samples, and the wettability results show moderate to strong correlations with rock properties. The results show that wettability indices predicted by the proposed technique exhibit more accurate correlations compared with those obtained by the volume-based method.
Geometry-induced capillary emptying Rascón, Carlos; Parry, Andrew O.; Aarts, Dirk G. A. L.
Proceedings of the National Academy of Sciences - PNAS,
11/2016, Letnik:
113, Številka:
45
Journal Article
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When a capillary is half-filled with liquid and turned to the horizontal, the liquid may flow out of the capillary or remain in it. For lack of a better criterion, the standard assumption is that the ...liquid will remain in a capillary of narrow cross-section, and will flow out otherwise. Here, we present a precise mathematical criterion that determines which of the two outcomes occurs for capillaries of arbitrary crosssectional shape, and show that the standard assumption fails for certain simple geometries, leading to very rich and counterintuitive behavior. This opens the possibility of creating very sensitive microfluidic devices that respond readily to small physical changes, for instance, by triggering the sudden displacement of fluid along a capillary without the need of any external pumping.
Applications of the fractal theory to analyze transport properties of porous media in science and engineering have received steady attention in the past two decades. However, the theory was rarely ...used to analyze invasion by extraneous fluids into a permeable bed where there is initially no such fluid present. Spills and leaks of non-aqueous phase liquids (NAPLs) and formation damage in drilling and completion wells are two typical examples. In this work, a fractal capillary model is proposed to analyze the depth of extraneous fluid invasion, where the tortuosity of capillaries and capillary pressure effect are taken into account. The quantitative relationship between average flow velocity and average beeline velocity are discussed based on the fractal geometry theory. Based on the proposed model, the depth of extraneous fluid invasion can be determined when the operation conditions, extraneous fluid properties and formation structure parameters are available, and the model predictions are in good agreement with the available data.
•Predicting capillary trapping using finite-volume simulation of two-phase flow directly on micro-CT images•Studying effects of capillary number, flow direction and initial saturation on the residual ...non-wetting phase saturation•Comparison with experimental measurements and network modelling
We study capillary trapping in porous media using direct pore-scale simulation of two-phase flow on micro-CT images of a Berea sandstone and a sandpack. The trapped non-wetting phase saturations are predicted by solving the full Navier–Stokes equations using a volume-of-fluid based finite-volume framework to simulate primary drainage followed by water injection. Using these simulations, we analyse the effects of initial non-wetting-phase saturation, capillary number and flow direction on the residual saturation. The predictions from our numerical method are in agreement with published experimental measurements of capillary trapping curves. This shows that our direct simulation method can be used to elucidate the effect of pore structure and flow pattern of capillary trapping and provides a platform to study the physics of multiphase flow at the pore scale.
A miniaturepolymer Bragg grating (PBG) sensor is fabricated and employed for ultrasonic imaging of seismic physical models (SPMs). The sensing Bragg grating is inscribed into an ultraviolet (UV) glue ...polymer waveguide with a femtosecond laser. The uniform polymer waveguide is fabricated by sealing the UV glue into a capillary fibre through capillary effect. By using line-by-line inscription technique, the laser beam is scanned transversely to periodically modulate the refractive index of the polymer waveguide, leading to the formation of the PBGs with various grating lengths. The sensor response to ultrasonic waves are investigated experimentally. When compared to single-mode fiber Bragg grating and phase-shifted fiber Bragg grating, the PBG with the same reflectivity presents a higher response amplitude due to its lower Young's modulus. Besides, the sensor has a good spectral stability when transferred from air to water due to the waterproof coating on the sensor end. Finally, the sensor is used to scan a large-scale 3D SPM and the structural features, such as fault, fluctuation, and depositional termination, can be distinctly reconstructed. The proposed PBG sensor provides a new technique with easy fabrication, high sensitivity, and good stability for high-fidelity ultrasonic imaging of seismicphysical models.
Detailed knowledge of the behaviour of rocks under thermal stress is essential in a variety of fields such as the exploitation of oil and mineral resources, the geothermal sector, the storage of ...radioactive liquid waste, or even CO2 capture and storage.
Granites are widely studied and exploited in these fields, and they show different reactions to high-temperature and thermal cycles due mainly to their high mineralogical and textural heterogeneity. One of the features that influences the most the thermal response is the porosity.
The objective of this study is to evaluate the influence of porosity when these rocks are exposed to different thermal treatments. For that purpose, experiments were carried out on four granitoids selected by their similar crystal size, but with variable mineral proportion and porosity values, ranging from 1 to 6%. Two kinds of tests were performed: i) progressive heating cycles from 90 °C to 130 °C to determine the critical threshold for thermal damage; ii) thermal fatigue with cycles of heating-cooling up to 200 °C.
The porosity and the water transport phenomena of the samples were characterised before and after each cycle by the monitoring of capillary water uptake coupled with infrared thermography. This technique allowed to follow the capillary fringe migration during the test and the evolution of the cooling rate index. The direct assessment of the damage was carried out by mercury injection porosimetry, optical polarising microscopy, and scanning electron microscopy.
The combination of all the results permitted to establish a link between the evolution of temperature and the modification of porous networks in granitoids. Microcracks appeared distinctly at a temperature between 90 °C to 130 °C for high porosity granitoids whose Quartz/Feldspar ratio was close to 1. For higher temperatures, the low porosity granitoids develop microcracks from the first heating cycle. The porosity then showed a stronger impact on thermal behaviour than the effect of the mineralogy. The results obtained from infrared thermography allowed to detect the strong variations in the microstructure.
•The initial heterogeneity of a granite generates a different cracking threshold for the same type of granite.•Repeated heating leads to increasing damage to rocks•The initial porosity and the quartz/feldspar ratio play a role in the thermal behaviour of granite.•Infrared thermography is a promising tool to detect microcracking.
Numerical modeling of immiscible two‐phase flow in deformable porous media has become increasingly significant due to its applications in oil reservoir engineering, geotechnical engineering and many ...others. The coupling between two‐phase flow and geomechanics gives rise to a major challenge to the development of physically consistent mathematical models and effective numerical methods. In this article, based on the concept of free energies and guided by the second law of thermodynamics, we derive a thermodynamically consistent mathematical model for immiscible two‐phase flow in poro‐viscoelastic media. The model uses the fluid and solid free energies to characterize the fluid capillarity and solid skeleton elasticity, so that it rigorously follows an energy dissipation law. The thermodynamically consistent formulation of the pore fluid pressure is naturally derived for the solid mechanical equilibrium equation. Additionally, the model ensures the mass conservation law for both fluids and solids. For numerical approximation of the model, we propose an energy stable and mass conservative numerical method. The method herein inherits the energy dissipation law through appropriate energy approaches and subtle treatments for the coupling between two phase saturations, the effective pore pressure and porosity. Using the locally conservative cell‐centered finite difference methods on staggered grids with the upwind strategies for saturations and porosity, we construct the fully discrete scheme, which has the ability to conserve the masses of both fluids and solids as well as preserve the energy dissipation law at the fully discrete level. In particular, the proposed method is an unbiased algorithm, that is, treating the wetting phase, the non‐wetting phase and the solid phase in the same way. Numerical results are also given to validate and verify the features of the proposed model and numerical method.
Capillary Wrinkling of Floating Thin Polymer Films Huang, Jiangshui; Juszkiewicz, Megan; de Jeu, Wim H ...
Science (American Association for the Advancement of Science),
08/2007, Letnik:
317, Številka:
5838
Journal Article
Recenzirano
A freely floating polymer film, tens of nanometers in thickness, wrinkles under the capillary force exerted by a drop of water placed on its surface. The wrinkling pattern is characterized by the ...number and length of the wrinkles. The dependence of the number of wrinkles on the elastic properties of the film and on the capillary force exerted by the drop confirms recent theoretical predictions on the selection of a pattern with a well-defined length scale in the wrinkling instability. We combined scaling relations that were developed for the length of the wrinkles with those for the number of wrinkles to construct a metrology for measuring the elasticity and thickness of ultrathin films that relies on no more than a dish of fluid and a low-magnification microscope. We validated this method on polymer films modified by plasticizer. The relaxation of the wrinkles affords a simple method to study the viscoelastic response of ultrathin films.
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