Direct Flow Visualization Research Articles

Visualization of the Characteristics of Polymer Gel Plugging of Fracture in the Multi-Slug Process

Abstract Polymer gel is a promising system for conformance control and water shutoff in water flooding reservoirs. However, the presence of fractures in reservoirs poses a major challenge to the successful application of polymer gels. This is because direct visualization of polymer gel system flow in the fracture is still lacking. In this paper, the HPAM/CrAc gel system was used to study the transport and plugging characteristics of gel multi-slug plugging using a visualized fracture model. The experimental results showed that multi-slug plugging accompanied by gradual compaction significantly improved the blocking strength of the polymer gel within the fracture. Specifically, multi-slug plugging improves the pressure gradient of the chasing water by approximately 80-200 kPa/m compared to one-step plugging of the polymer gel. During multi-slug plugging of the fracture, the later injected gelant slugs pass through the weak areas of the prior matured gel slugs and continue to move behind them instead of pushing the prior matured gel as a whole to the distal portion of the fracture. After the polymer gel one-step plugging of the fracture, chasing water will pass through the edges of the fracture where the gel is not adequately filled or directly through the mature gel in the form of wormholes. In contrast, after multi-slug plugging of the fracture, the mature gel is not easy to be breached by chasing water because of the compaction effect, while the junction between the mature gels of each slug will become an easy area for chasing water to break through. But it is still more difficult to break through than the one-step plugging process. This research is informative for the improvement of polymer gel systems and their successful application in fractured reservoirs for conformance control and water shutoff.

ANALYSIS OF THERMAL PERFORMANCE IN A TWO-PHASE THERMOSYPHON LOOP BASED ON FLOW VISUALIZATION AND AN IMAGE PROCESSING TECHNIQUE

Thermal performance was analyzed based on flow visualization and an image processing technique in a two-phase thermosyphon loop (TPTL) with boiling water as the working fluid at low pressure. The bubble geometries, bubble frequency, and dynamic void fraction were estimated using direct image analysis combined with the power spectrum and statistical analysis. At a heating rate of 400 W and a filling ratio of 0.88, the thermal performance of the TPTL was enhanced with a thermal efficiency of 91% and effective thermal conductivity of 11,336 Wm<sup>-1</sup> °C<sup>-1</sup>. The enhancement was due to the higher frequency cap bubble flow of 11.2 Hz obtained by the direct flow visualization. The bigger Taylor bubbles with slug flow were examined to contribute to the negative effect on the heat transfer rate due to their film boiling regimes. The detailed analysis reveals the mechanism of bubble flow interacting with thermal performance.

Core analysis in a changing world – how technology is radically benefiting the methodology to acquire, the ability to visualize and the ultimate value of core data

Abstract Core analysts principally study the storage, flow and saturation properties of porous rocks and sediments. Some of the derived parameters are specific to hydrocarbon production but many have commonality with other subsurface disciplines such as hydrology and soil science. Traditional core analysis involves direct physical experimentation on core plugs to derive a range of parameters used as calibration for conventional well logs, and to predict hydrocarbon reserves and recovery. The mechanisms and processes for obtaining such data have evolved significantly during the last century, from the manual instruments of the mid-twentieth century to the accredited digital data collection and recording of the 1990s onwards. X-ray micro- and nano-scale computed tomography (CT) imaging led to the development of the digital rock physics subdiscipline in the early 2000s. This has subsequently allowed direct visualization of fluid flow at the pore scale, imaging the wetting phase and multiphase fluid mobility. Multiscale imaging workflows are being developed to overcome issues around heterogeneous rock and the limited field of view associated with the highest resolution X-ray CT images. Hybrid workflows, which combine digital rock physics with traditional core analysis, are becoming increasingly common to meet the challenges associated with some of the most difficult to constrain properties, such as relative permeability. At a larger scale, the recent development of multisensor core logging (MSCL) tools has allowed the cost-effective acquisition of essentially continuous high-resolution 1D, 2D and 3D datasets from both slabbed and unslabbed whole core. Often aided by artificial intelligence to manage and interpret these large physical and chemical datasets, both new and legacy core can be rapidly screened to allow representative subsampling for detailed laboratory experimentation. The context and data provided by the MSCL then allows effective upscaling of these time- and cost-intensive point-source measurements. In the last decade, extended reality (XR) has resulted in a step change in the ability to visualize and integrate core and core-derived information with other subsurface datasets. A very wide range of scales can be managed effectively, from micrometre- to centimetre-scale petrographical and core analysis data, to metre-scale well logs and up to kilometre-scale 3D and 4D seismic. These tools allow stakeholders to work and meet from any location in a common workspace, and efficiently scale and interrogate data in a virtual 3D environment. The various advances in core analysis and associated technologies during the early twenty-first century mean that the study of porous media to help enable the energy transition looks assured. During the coming decades, applications as diverse as carbon capture, utilization and storage (CCUS), hydrogen storage, geothermal energy generation, mining for critical minerals, palaeoclimate studies, radioactive waste management, and site surveys for windfarms will all continue to benefit from the data and understanding derived from core analysis.

Abstract P2095: Capillary Stalling by Neutrophils is a Novel Mechanism Underlying Myocardial Hypoperfusion in Heart Failure with Preserved Ejection Fraction

Background: Chronic inflammation and myocardial hypoperfusion are implicated in the pathogenesis of heart failure with preserved ejection fraction (HFpEF), but the cellular and molecular mechanisms are unknown. Intravital cardiac multiphoton microscopy (MPM) enables direct visualization of blood flow and inflammatory cells within the capillary bed of the actively beating heart. We hypothesize that transient arrest of neutrophils in myocardial capillaries leads to perfusion deficits, resulting in hypoxia and driving disease progression. Methods: Male and female 8-12-week-old C57BL/6 mice received a high fat diet and L-NAME in drinking water (HFpEF) or standard diet and water (Chow) for 15 weeks. Intravital imaging of the actively beating heart was performed in mechanically ventilated mice to visualize neutrophils and capillary perfusion. An antibody against the neutrophil surface marker Ly6G (αLy6G) was administered intraperitoneally to test the effect of neutrophil depletion. Results: In vivo MPM revealed increases in arrested neutrophils in myocardial capillaries in HFpEF mice compared to Chows. Myocardial hypoxia, assessed by pimonidazole staining, and diastolic function, assessed as mitral e/e’ using echocardiography, were rescued with both extended neutrophil depletion (2mg/kg every 3d for 4 wk) and acutely (24 hrs after a single dose of 4mg/kg). To further test the immediate effects of αLy6G we implemented multi-exposure laser speckle imaging for perfusion and spectral imaging for tissue and blood oxygenation with electrocardiograph-driven reconstruction. Conclusion: Arrested neutrophils within capillaries appear to compromise myocardial perfusion in HFpEF. Neutrophil depletion to restore blood flow improved myocardial oxygenation and diastolic function rapidly. Effects were sustained with prolonged treatment. Capillary stall perfusion deficits may be a future therapeutic target to slow disease progression and offer rapid symptomatic relief.

Friction dynamics of elasto-inertial turbulence in Taylor-Couette flow of viscoelastic fluids.

Dynamic properties of elasto-inertial turbulence (EIT) are studied in a Taylor-Couette geometry. EIT is a chaotic flow state that develops upon both non-negligible inertia and viscoelasticity. A combination of direct flow visualization and torque measurement allows to verify the earlier onset of EIT compared with purely inertial instabilities (and inertial turbulence). The scaling of the pseudo-Nusselt number with inertia and elasticity is discussed here for the first time. Variations in the friction coefficient, temporal frequency spectra and spatial power density spectra highlight that EIT undergoes an intermediate behaviour before transitioning to its fully developed chaotic state that requires both high inertia and elasticity. During this transition, the contribution of secondary flows to the overall friction dynamics is limited. This is expected to be of great interest in the aim of achieving efficiency mixing at low drag and low but finite Reynolds number. This article is part of the theme issue "Taylor-Couette and related flows on the centennial of Taylor's seminal Philosophical transactions paper (Part 2)".

Characteristics and Limitations of Video-capillaroscopy in Reconstructive Microsurgery for Different Histologic Components of Flaps.

Indocyanine green, ultrasonography, and handheld Doppler can be used to evaluate blood flow at the donor and recipient site during microvascular reconstruction. However, these methods do not provide direct visualization and assessment of real-time blood flow. Video-capillaroscopy has been shown to be useful in clinical practice to assess microcirculation in rheumatologic disorders. In this report we used video-capillaroscopy to assess different tissue components involved in microvascular surgery. Seven patients who underwent head and neck oncologic microvascular reconstruction between November 2021 and February 2022 were included in this study. Video-capillaroscopy (GOKO-BscanZD, GOKO Imaging Devices Co., Ltd., Japan) was used to evaluate the donor-site and recipient-site tissue components. Optimal red blood cell movement was graded with a score of four, while no flow was graded with a score of 0. Seven myocutaneous flaps and seven recipient sites were evaluated. For the donor-site, our analysis demonstrated a significantly higher video-capillaroscopy quality for skin (3.43), adipose tissue (3.7) and perforators (3.7) when compared with muscle (0.429), muscle fascia (0.857), and de-epithelialized skin (1) (P < 0.001). For the recipient-site, a significantly higher video-capillaroscopy quality for skin (2.7), adipose tissue (3.5), and the periosteum (2.1) was noted when compared with muscle (0) (P < 0.001). Video-capillaroscopy efficiency is limited in the muscular component and injured (de-epithelialized) skin surface areas of flaps. Herein, we provide evidence that assessment of flap perfusion with video-capillaroscopy can be reliably achieved in the skin, periosteum, perforators, and adipose tissue. Video-capillaroscopy is expected to be applied for intraoperative real-time blood flow evaluation.

Visualization of adaptive polymer flow and displacement in medium-permeable 3D core-on-a-chip

Polymer flooding has been witnessed an effective technology for enhancing oil recovery from medium-to low-permeability reservoirs; however, direct visualization of polymer solution flow in such reservoir condition is still lacking. In this work, a three-dimensional (3D) core-on-a-chip device with a permeability of around 200 mD was prepared and employed to visualize the pore-scale flow and displacement of a self-adaptive polymer (SAP, 8.7 × 106 g·mol−1)−whose microscopic association structure and macroscopic viscosity can reversibly change in response to shear action−versus partially hydrolyzed polyacrylamide (HPAM), by recording their flow curves, monitoring dynamic transportation process via particle imaging velocimetry, and building 3D structure of remaining oil. The results show that, in single-phase flow, all polymer solutions exhibit flow thinning and then thickening regions as flow rate increases, but the transition between two regimes occurs at a small Weissenberg number (10−3−10−1) in this medium-permeable condition. In contrast to HPAM-1 with close weight-average molecular weight (Mw), the adaptive character not only extends SAP's shear-govern region, allowing SAP to propagate piece by piece and achieve higher accessible pore volume, but it also enhances the elastic resistibility of polymer in the extension-dominated regime, increasing the microscopic displacement efficiency. These two effects result in 1.5–3 times more oil recovery factor for SAP than for HPAM-1. Regarding ultra-high-Mw HPAM-2 (25 × 106 g·mol−1), plugging and chain degradation do occur, thus producing lower oil recovery than SAP. This work provides a direct approach for in-situ assessment of polymer-based displacing system under a more authentic condition of practical reservoirs.

Fabrications and Applications of Micro/Nanofluidics in Oil and Gas Recovery: A Comprehensive Review

Understanding fluid flow characteristics in porous medium, which determines the development of oil and gas oilfields, has been a significant research subject for decades. Although using core samples is still essential, micro/nanofluidics have been attracting increasing attention in oil recovery fields since it offers direct visualization and quantification of fluid flow at the pore level. This work provides the latest techniques and development history of micro/nanofluidics in oil and gas recovery by summarizing and discussing the fabrication methods, materials and corresponding applications. Compared with other reviews of micro/nanofluidics, this comprehensive review is in the perspective of solving specific issues in oil and gas industry, including fluid characterization, multiphase fluid flow, enhanced oil recovery mechanisms, and fluid flow in nano-scale porous media of unconventional reservoirs, by covering most of the representative visible studies using micro/nanomodels. Finally, we present the challenges of applying micro/nanomodels and future research directions based on the work.

Global and local performances of a tubular micro-pulsating heat pipe: experimental investigation

Heat exchanger optimization is mandatory in almost any industrial application. Thanks to their performances, the Pulsating Heat Pipes (PHPs) are a very interesting application. Micro-PHPs, which are defined as PHPs with a tube that has a hydraulic diameter < 500 μm, have shown big advantages in terms of their ability to dissipate high heat fluxes, their reduced size, and their low weight. However, the great majority of the works that investigate the thermal behavior of micro-PHPs only deal with the average performance of the system, usually represented in terms of global thermal resistance of the device. Our study aims to begin to fill this lack by investigating the local thermal behavior of a typical multi-turn micro-PHP. A micro-PHP characterized by seven turns and realized with a stainless-steel pipe was investigated. It was positioned in a vertical position, with the evaporator at the bottom, and it was partially loaded with HFC-134a. The studied micro-PHP is tubular, while almost the totality of the micro-PHPs investigated to date are constituted by microchannels engraved in silicon-based wafer, and they present a great potential in terms of three-axis flexibility compared to the flat micro-PHPs that are usually investigated. To highlight the different thermal functioning of each turn, an infrared camera was used to acquire the local temperature distributions on the wall of the PHP condenser. It was found that the best performance was reached for a filling ratio of 46% and for a heat input ranging between 1.9–3.7 W. To thoroughly study the pulsating behavior of the proposed PHP, the dominant frequencies were investigated by performing a wavelet analysis. The results allow the identification of different flow regimes, such as start-up, non-persistent oscillating flow (0.05–0.6 Hz; Qnet < 2.3 W), and quasi-periodic oscillating flow (0.6–1.5 Hz; Qnet = 2.8–4.7 W). Eventually, the results highlight that the approach proposed herein can provide worthy evidence about the fluid motion inside the PHP, thereby allowing to overcome the limits introduced by the adoption of transparent materials for the direct flow visualization or by the invasive insertion of pressure sensors, particularly in devices with such small dimensions.

In Situ Visualization of Localized Surface Plasmon Resonance-Driven Hot Hole Flux.

Nonradiative surface plasmon decay produces highly energetic electron–hole pairs with desirable characteristics, but the measurement and harvesting of nonequilibrium hot holes remain challenging due to ultrashort lifetime and diffusion length. Here, the direct observation of LSPR‐driven hot holes created in a Au nanoprism/p‐GaN platform using photoconductive atomic force microscopy (pc‐AFM) is demonstrated. Significant enhancement of photocurrent in the plasmonic platforms under light irradiation is revealed, providing direct evidence of plasmonic hot hole generation. Experimental and numerical analysis verify that a confined |E|‐field surrounding a single Au nanoprism spurs resonant coupling between localized surface plasmon resonance (LSPR) and surface charges, thus boosting hot hole generation. Furthermore, geometrical and size dependence on the extraction of LSPR‐driven hot holes suggests an optimized pathway for their efficient utilization. The direct visualization of hot hole flow at the nanoscale provides significant opportunities for harnessing the underlying nature and potential of plasmonic hot holes.

Enhanced wall shear stress prevents obstruction by astrocytes in ventricular catheters.

The treatment of hydrocephalus often involves the placement of a shunt catheter into the cerebrospinal ventricular space, though such ventricular catheters often fail by tissue obstruction. While diverse cell types contribute to the obstruction, astrocytes are believed to contribute to late catheter failure that can occur months after shunt insertion. Using in vitro microfluidic cultures of astrocytes, we show that applied fluid shear stress leads to a decrease of cell confluency and the loss of their typical stellate cell morphology. Furthermore, we show that astrocytes exposed to moderate shear stress for an extended period of time are detached more easily upon suddenly imposed high fluid shear stress. In light of these findings and examining the range of values of wall shear stress in a typical ventricular catheter through computational fluid dynamics (CFD) simulation, we find that the typical geometry of ventricular catheters has low wall shear stress zones that can favour the growth and adhesion of astrocytes, thus promoting obstruction. Using high-precision direct flow visualization and CFD simulations, we discover that the catheter flow can be formulated as a network of Poiseuille flows. Based on this observation, we leverage a Poiseuille network model to optimize ventricular catheter design such that the distribution of wall shear stress is above a critical threshold to minimize astrocyte adhesion and growth. Using this approach, we also suggest a novel design principle that not only optimizes the wall shear stress distribution but also eliminates a stagnation zone with low wall shear stress, which is common to current ventricular catheters.

3D manufacturing of intracranial aneurysm biomodels for flow visualizations: Low cost fabrication processes

There is a continuous search for better and more complete in vitro models with mechanical properties closer to in vivo conditions. In this work a manufacturing process, based on a lost core casting technique, is herein reported to produce aneurysm biomodels to perform experimental hemodynamic studies. By using real artery images combined with a lost core casting technique, three materials were tested: paraffin, beeswax and glycerin-based soap. All in vitro biomodels were compared according to their transparency and final structure. Additionally, comparisons between experimental and numerical flow studies were also performed. The results have shown that the biomodels produced with beeswax and glycerine-based soap were the most suitable in vitro models to perform direct flow visualizations of particulate blood analogue fluids. The biomodels proposed in this works, have the potential to provide further insights into the complex blood flow phenomena happening at different kinds of pathologies and answer to important hemodynamics questions that otherwise cannot be tackled with the existing in vitro models.

Evaluation of Cardiac Shunts With 4D Flow Cardiac Magnetic Resonance: Intra- and Interobserver Variability.

In the last decade, the capacity of magnetic resonance (MR) to evaluate congenital anomalies has improved substantially. To date, only a few studies have evaluated the value of 4D-flow MRI in shunt assessments. To assess the intra- and interobserver variability of 4D-flow MRI in patients diagnosed with cardiac/extracardiac shunt. Secondarily, to assess the feasibility of directly measuring the shunt and to determine the prognostic correlation with the pulmonary-to-systemic (Qp/Qs) flow ratio. Retrospective. In all, 18 patients with cardiac shunt diagnosis. 1.5 T/4D phase-contrast MRI. Pulmonary and systemic flows were measured at different locations to assess the internal consistency by two observers (twice by one, and once by the other). The Qp/Qs ratio was calculated. When feasible, direct flow was quantified by planimetry. Spearman's rho correlation coefficient was used to assess the relationship between pulmonary/systemic flows measured at different levels and to compare the jet characteristics with prognostic data as right ventricle volume. Intra- and interobserver variability were determined by Bland-Altman plots and interobserver correlation. The most common shunt type (n = 10; 55.5%) was ostium secundum atrial septal defect (ASD). Direct visualization and quantification of shunt flow was possible in all studies. Pulmonary and systemic flows showed a strong correlation between these measures (Spearman's rho [r] of 0.872 and 0.899). The mean Qp/Qs ratio was 1.61(0.62). Mean flow rate was 2.01(1.68) l/min. The mean jet diameter was 11.88 (5.44) mm. Intraobserver (r = 0.97) and interobserver correlation (ICC = 0.95) for the Qp/Qs calculation were both excellent. Direct measurement of flow was strongly correlated (r = 0.98; ICC = 0.95). Correlation was strong between Qp/Qs and direct jet flow (r = 0.76 and 0.77), Qp/Qs and mean jet diameter (r = 0.79 and 0.94), and Qp/Qs with jet area (r = 0.77 and 0.94). Measurement of the Qp/Qs ratio and direct shunt quantification using 4D-flow MRI was feasible, and highly reproducible. Internal consistency was excellent, with low intra- and interobserver variability. Correlation between the Qp/Qs ratio, direct flow measurement, mean diameter, and jet area was strong. 3 TECHNICAL EFFICACY: Stage 2 J. Magn. Reson. Imaging 2020;52:1055-1063.

Experimental investigation of the flow in a micro-channelled combustor and its relation to flame behaviour

The dynamic behaviour of periodic laminar premixed acetylene-air flames in a micro-channelled combustor consisting of an array of five planar rectangular channels was found to be influenced by the equivalence ratio and flow-rate of the continuously and steadily injected premixed fuel charge. Three distinct flame stages were observed — planar, chaotic and trident, which were strongly correlated to the flow dynamics. The effect of the flow on the flame behaviour was investigated by characterizing the cold flow in a scaled-up model channel with the same aspect ratio as the combustion micro-channel. Direct flow visualization using flow tracers and quantitative velocity-field data from PIV measurements showed both an increase in the bottom recirculation zone reattachment length (along the floor of the channel) and a decrease in the lateral recirculation zone reattachment length (along the sides of the channel) with increasing flow Reynolds number. Comparison of the flow and flame transition locations downstream of the injection point suggested that the location of trident flame onset coincides with the flow bottom recirculation zone reattachment length. The planar-chaotic flame transition location was observed to be influenced by the homogeneity of the mixture downstream of the injection plane.

Value of pancreatic and biliary flow MR imaging in the evaluation of pancreaticobiliary disorders.

Researchers have examined the possibility of studying pancreatic and biliary flow and using to aid the pathological evaluation of pancreaticobiliary diseases. Recently, a new method using MR imaging (MRI) has been developed for the direct visualization of pancreatic juice flow, based on a spin labeling technique. This technique enables direct visualization of pancreatic or bile duct juice flow and has various clinical applications relating to pancreaticobiliary disease. This review discusses the principle of pancreatic and biliary flow MRI with spin labeling and typical application examples such as the evaluation of the exocrine function of the pancreas in cases of chronic pancreatitis and the visualization of pancreatic juice reflux into the bile duct. Moreover other application is also discussed.

On the near-field interfaces of homogeneous and immiscible round turbulent jets

Quantifying accidental opaque discharges is a challenging task, since probing beyond their visible interfaces may be difficult or impossible. In this case, we show that the visible interface features near the jet exit can be used to gauge the flow. This work examines the interface in the near-field features of submerged homogeneous and immiscible turbulent jets. Experiments were carried out with water jets and immiscible silicone oil jets of two viscosities in a water tank. The jet Reynolds numbers are in the range of $Re\sim 4500{-}50\,000$ for homogeneous water jets and $Re\sim 3500{-}27\,000$ for silicone oil jets in water. The jet fluids are made visible by doping with fluorescent dye and excitation with directional illumination. The jet interfaces are continuous and convoluted for water jets, while convoluted and discontinuous with droplets and ligaments for oil jets. Direct flow visualization, schlieren photography, shadowgraph photography and particle image velocimetry are employed as appropriate. Interface length scales are characterized using various image processing techniques. Droplet sizes are quantified using Hough transformation. Interface length scales decrease with Reynolds number and increase gradually with distance from the exit plane for a given Reynolds number. These scales are isotropic for the homogeneous water jets and exhibit a streamwise-to-cross-stream ratio of approximately 1.3 for the oil jets. Interfacial tension, hence the Weber number, determines the average droplet size in the immiscible jets.

Direct Flow Visualization of Complex Behavior in the Disk-Normal Planes of Rotating Flow driven by Corotating Disks Mounted in a Non-Axisymmetric Enclosure

Direct Flow Visualization of Complex Behavior in the Disk-Normal Planes of Rotating Flow driven by Corotating Disks Mounted in a Non-Axisymmetric Enclosure

Fluid-flow pressure measurements and thermo-fluid characterization of a single loop two-phase passive heat transfer device

A Novel Single Loop Pulsating Heat Pipe (SLPHP), with an inner diameter of 2 mm, filled up with two working fluids (Ethanol and FC-72, Filling Ratio of 60%), is tested in Bottom Heated mode varying the heating power and the orientation. The static confinement diameter for Ethanol and FC-72, respectively 3.4 mm and 1.7mm, is above and slightly under the inner diameter of the tube. This is important for a better understanding of the working principle of the device very close to the limit between the Loop Thermosyphon and Pulsating Heat Pipe working modes. With respect to previous SLPHP experiments found in the literature, such device is designed with two transparent inserts mounted between the evaporator and the condenser allowing direct fluid flow visualization. Two highly accurate pressure transducers permit local pressure measurements just at the edges of one of the transparent inserts. Additionally, three heating elements are controlled independently, so as to vary the heating distribution at the evaporator. It is found that peculiar heating distributions promote the slug/plug flow motion in a preferential direction, increasing the device overall performance. Pressure measurements point out that the pressure drop between the evaporator and the condenser are related to the flow pattern. Furthermore, at high heat inputs, the flow regimes recorded for the two fluids are very similar, stressing that, when the dynamic effects start to play a major role in the system, the device classification between Loop Thermosyphon and Pulsating Heat Pipe is not that sharp anymore.

Real rock-microfluidic flow cell: A test bed for real-time in situ analysis of flow, transport, and reaction in a subsurface reactive transport environment

Physical, chemical, and biological interactions between groundwater and sedimentary rock directly control the fundamental subsurface properties such as porosity, permeability, and flow. This is true for a variety of subsurface scenarios, ranging from shallow groundwater aquifers to deeply buried hydrocarbon reservoirs. Microfluidic flow cells are now commonly being used to study these processes at the pore scale in simplified pore structures meant to mimic subsurface reservoirs. However, these micromodels are typically fabricated from glass, silicon, or polydimethylsiloxane (PDMS), and are therefore incapable of replicating the geochemical reactivity and complex three-dimensional pore networks present in subsurface lithologies. To address these limitations, we developed a new microfluidic experimental test bed, herein called the Real Rock-Microfluidic Flow Cell (RR-MFC). A porous 500μm-thick real rock sample of the Clair Group sandstone from a subsurface hydrocarbon reservoir of the North Sea was prepared and mounted inside a PDMS microfluidic channel, creating a dynamic flow-through experimental platform for real-time tracking of subsurface reactive transport. Transmitted and reflected microscopy, cathodoluminescence microscopy, Raman spectroscopy, and confocal laser microscopy techniques were used to (1) determine the mineralogy, geochemistry, and pore networks within the sandstone inserted in the RR-MFC, (2) analyze non-reactive tracer breakthrough in two- and (depth-limited) three-dimensions, and (3) characterize multiphase flow. The RR-MFC is the first microfluidic experimental platform that allows direct visualization of flow and transport in the pore space of a real subsurface reservoir rock sample, and holds potential to advance our understandings of reactive transport and other subsurface processes relevant to pollutant transport and cleanup in groundwater, as well as energy recovery.

From flow focusing to vortex formation in crossing microchannels

The paper is concerned with the experimental and numerical investigations of the vortex formation and flow focusing inside a cross-shaped microchannel domain. The local hydrodynamics in the junction area, upstream of the focusing region, is analyzed with the aim to characterize the onset and the evolution of the vortical structures, in correlation with the operating parameters. The numerical simulations based on a finite-volume approach are validated by direct flow visualizations using epifluorescence and confocal microscopy. The main result of the study is a flow pattern map, providing comprehensive information on the flow dynamics inside the microchannel junction as a function of the input flow rates and the corresponding Reynolds numbers. The flow pattern map identifies the limits of the flow focusing regime and the critical values of the parameters at which the vortical structures are formed. Beyond the breakdown of the classical flow focusing scenario with one focused output stream, flow patterns with two and four output streams are identified.