Capillary Pressure Difference Research Articles

Patterned catalyst layer boosts the performance of proton exchange membrane fuel cells by optimizing water management

• Patterned catalyst layer prepared with a simple one-step impressing method. • FEA results indicate that grooves and convex accumulate water and gas respectively. • The separation of gas and water transport paths avoids confliction of mass flow. • Maximum power density increased by 10% compared with untreated one’s. Mass transport is crucial to the performance of proton exchange membrane fuel cells, especially at high current densities. Generally, the oxygen and the generated water share same transmission medium but move towards opposite direction, which leads to serious mass transfer problems. Herein, a series of patterned catalyst layer were prepared with a simple one-step impressing method using nylon sieves as templates. With grooves 100 μm in width and 8 μm in depth on the surface of cathode catalyst layer,the maximum power density of fuel cell increases by 10% without any additional durability loss while maintaining a similar electrochemical surface area. The concentration contours calculated by finite element analysis reveal that the grooves built on the surface of catalyst layer serve to accumulate the water nearby while oxygen tends to transfer through relatively convex region, which results from capillary pressure difference caused by the pore structure difference between the two regions. The separation of oxidant gas and generated water avoids mass confliction thus boosts mass transport efficiency.

Effects of Metoprolol on Exercise Hemodynamics in Patients With Obstructive Hypertrophic Cardiomyopathy

BackgroundThe relationship between exercise hemodynamics, loading conditions, and medical treatment in patients with obstructive hypertrophic cardiomyopathy (HCM) is incompletely understood. ObjectivesThis study aimed to investigate the effect of metoprolol on invasive hemodynamic parameters at rest and during exercise in patients with obstructive HCM. MethodsThis randomized, double-blind, placebo-controlled crossover trial enrolled 28 patients with obstructive HCM and New York Heart Association functional class ≥II. Patients were randomized to initiate either metoprolol 150 mg or placebo for 2 consecutive 2-week periods. Right-heart catheterization and echocardiography were performed at rest and during exercise at the end of each treatment period. The primary outcome was the difference in pulmonary capillary wedge pressure (ΔPCWP) between peak exercise and rest. ResultsNo treatment effect on ΔPCWP was observed between metoprolol and placebo treatment (21 ± 9 mm Hg vs 23 ± 9 mm Hg; P = 0.12). At rest, metoprolol lowered heart rate (P < 0.0001), left ventricular outflow tract (LVOT) gradient (P = 0.01), and increased left ventricular end-diastolic volume (P = 0.02) and stroke volume (SV) (+6.4; 95% CI: 0.02-17.7; P = 0.049). During peak exercise, metoprolol was associated with a lower heart rate (P < 0.0001), a lower LVOT gradient (P = 0.0005), lesser degree of mitral regurgitation (P = 0.004), and increased SV (+9 mL; 95% CI: 2-15 mL; P = 0.008). ConclusionsIn patients with obstructive HCM, exercise was associated with an abnormal rise in PCWP, which was unaffected by metoprolol. However, metoprolol increased SV at rest and peak exercise following changes in end-diastolic volume, LVOT gradient, and degree of mitral regurgitation. (The Effect of Metoprolol in Patients With Hypertrophic Obstructive Cardiomyopathy [TEMPO]; NCT03532802)

Capillaric field effect transistors

Controlling fluid flow in capillaric circuits is a key requirement to increase their uptake for assay applications. Capillary action off-valves provide such functionality by pushing an occluding bubble into the channel using a difference in capillary pressure. Previously, we utilized the binary switching mode of this structure to develop a powerful set of fundamental fluidic valving operations. In this work, we study the transistor-like qualities of the off-valve and provide evidence that these structures are in fact functionally complementary to electronic junction field effect transistors. In view of this, we propose the new term capillaric field effect transistor to describe these types of valves. To support this conclusion, we present a theoretical description, experimental characterization, and practical application of analog flow resistance control. In addition, we demonstrate that the valves can also be reopened. We show modulation of the flow resistance from fully open to pinch-off, determine the flow rate–trigger channel volume relationship and demonstrate that the latter can be modeled using Shockley’s equation for electronic transistors. Finally, we provide a first example of how the valves can be opened and closed repeatedly.

Microfluidic Investigation of Foam Coarsening Dynamics in Porous Media at High-Pressure and High-Temperature Conditions

Coarsening or Oswald ripening, induced by interbubble gas diffusion, is considered to dominate foam structure evolution in porous media. We present the first study of trapped foam coarsening dynamics under realistic deep reservoir conditions (up to 3200 psi/22 MPa of pore pressure and 100 °C of temperature) in a high-pressure and high-temperature microfluidic system. The findings are expected to help predict foam structure evolution in applications such as enhanced oil recovery and CO2 geological sequestration. It is shown that, in porous media, larger bubbles grow at the expense of smaller bubbles. The growth rate of the average bubble area (⟨a⟩) over time shows a long-term linear increase when ⟨a⟩ is between 1/5 and 1/2 of the average pore size. The foam coarsening kinetics are determined by the liquid film permeability, gas-liquid interfacial tension, and the molar volume of the dispersed phase. In summary, foams prepared with less water-soluble gases (e.g., N2 and air) and lower foam quality show slower coarsening kinetics due to a lower film permeability. Foam coarsening is more sensitive to surfactant concentration (than surfactant type), as it determines the interfacial tension that controls the mass transfer driving force (capillary pressure difference). The transport properties of the dispersed phase depend strongly on its density, which increases with increasing pore pressure and decreasing temperature. At the same experimental conditions, gas CO2 foam shows a 10-fold faster coarsening rate than N2 foam. However, dense (i.e., liquid and supercritical) CO2 foams show a remarkable 20-500-fold reduction in coarsening kinetics compared with gas N2 and CO2 foams due to the significantly reduced mass transfer driving forces. In a sense, trapped CO2 foam can be stronger than N2 foam at high-pressure and high-temperature conditions.

Design and optimization of gradient wettability pore structure of adaptive PEM fuel cell cathode catalyst layer

The design of cathode catalyst layer (CL) is essential to improve the mass transfer capacity of proton exchange membrane (PEM) fuel cell and increase power density. In this work, cathode CL is divided into three sub-layers, and each sub-layer is added nano-particles with different wettability. The gradient CL with hydrophilic SiO2 particles at inner layer and hydrophobic polytetrafluoroethylene (PTFE) particles at outer layer significantly enhances the performance of membrane exchange assembly (MEA). Its performance is 895 mW/cm2@0.6 V, which is 24.1 %higher than CL without any particles (721 mW/cm2@ 0.6 V). Under operating conditions of high current density, high cathode humidity and high air stoichiometry, the gradient CL has only a little voltage loss. Through Electrochemical Impedance Spectroscopies (EIS) impedance analysis under high current density (1.8A/cm2), mass transfer resistance of gradient CL is 25.4 Ω, and is much smaller than the mass transfer resistance of the homogeneous CL of 35.1 Ω, which reflects the significant enhancement in mass transfer capacity of gradient CL. The gradient catalyst layer is suitable for a wider range of current density, humidity, and stoichiometry, but excessive cathode gas stoichiometry causes a decrease in performance, which is caused by excessive drainage capacity. In addition, 18 different gradient CLs are designed and manufactured, and the gradient CL with catalyst coated membrane (CCM) structure has the best performance. In gradient CL, increasing the capillary pressure difference between sublayers is the key to performance improvement. It is confirmed that the property of MEA with appropriate wettability gradient design can be significantly improved.

The Influence of Loop Heat Pipe Evaporator Porous Structure Parameters and Charge on Its Effectiveness for Ethanol and Water as Working Fluids.

This paper presents the results of experiments carried out on a specially designed experimental rig designed for the study of capillary pressure generated in the Loop Heat Pipe (LHP) evaporator. The commercially available porous structure made of sintered stainless steel constitutes the wick. Three different geometries of the porous wicks were tested, featuring the pore radius of 1, 3 and 7 µm. Ethanol and water as two different working fluids were tested at three different evaporator temperatures and three different installation charges. The paper firstly presents distributions of generated pressure in the LHP, indicating that the capillary pressure difference is generated in the porous structure. When installing with a wick that has a pore size of 1 μm and water as a working fluid, the pressure difference can reach up to 2.5 kPa at the installation charge of 65 mL. When installing with a wick that has a pore size of 1 μm and ethanol as a working fluid, the pressure difference can reach up to 2.1 kPa at the installation charge of 65 mL. The integral characteristics of the LHP were developed, namely, the mass flow rate vs. applied heat flux for both fluids. The results show that water offers larger pressure differences for developing the capillary pressure effect in the installation in comparison to ethanol. Additionally, this research presents the feasibility of manufacturing inexpensive LHPs with filter medium as a wick material and its influence on the LHP’s thermal performance.

Abstract 12535: The Hemodynamic Response to Exercise in Patients With Obstructive Hypertrophic Cardiomyopathy and the Effect of Metoprolol

Introduction: Patients with obstructive hypertrophic cardiomyopathy (HCM) frequently experience advanced heart failure symptoms at low levels of physical activity. The relationship between symptoms and loading conditions during exercise is incompletely understood. Whether standard treatment with beta-blockers affects exercise hemodynamics is unknown. Objectives: The aim of this study was to investigate the invasive hemodynamic response to exercise in moderately symptomatic patients with obstructive HCM, and how treatment with metoprolol affects this response. Method: This double-blinded, placebo-controlled, randomized crossover trial enrolled 28 patients with obstructive HCM and New York Heart Association functional class ≥ II from May 2018 to September 2020. Patients received metoprolol or placebo for two consecutive two-week periods in random order. During each treatment period, patients underwent right-heart catheterization at rest and during exercise. The primary outcome was the difference in pulmonary capillary wedge pressure (ΔPCWP) between peak exercise and rest. Results: There was no treatment effect on Δ PCWP between metoprolol and placebo treatment (21(9) mmHg versus 23(9) mmHg; p = 0.12). When comparing metoprolol to placebo treatment, there was no significant difference in PCWP at rest (15 (6) mmHg versus 13 (5) mmHg; p = 0.06) or at peak exercise (35 (12) mmHg versus 37 (10) mmHg; p = 0.38). At peak exercise, metoprolol treatment was associated with a higher stroke volume (101 (24) ml versus 92 (21) ml; p &lt; 0.01), a 25% lower heart rate (107 (19) beats/min versus 139 (23) beats/min; p &lt; 0.0001), and subsequently a lower cardiac output (10.8 (3.3) L/min versus 12.8 (3.2) L/min; p &lt; 0.0001). Conclusion: Exercise in patients with obstructive HCM is associated with a severe increase in left-sided filling pressures which are not affected by metoprolol treatment. Despite increased stroke volume during metoprolol treatment, cardiac output is reduced at peak exercise.

Hydrocarbon accumulation depth limit and implications for potential resources prediction

The horizontal distribution and periodic accumulation of hydrocarbon in reservoirs are well understood. However, our understanding on the vertical distribution of hydrocarbon accumulation in reservoirs is not clear and remains mysterious to some extent. We proposed a concept of hydrocarbon accumulation depth limit (HADL) to characterize the hydrocarbon’s vertical distribution in petroliferous basins, which is determined by statistical analyses of the variation trends of reservoir layers’ essential properties, including hydrocarbon saturations (So), movable hydrocarbon ratios (Mo) and dry layer ratio (Ko), when the depth is increased. A total of 80,762 drilling results from 12,237 exploration wells in six representative petroliferous basins in China were collected and analyzed. The reservoir layers’ essential properties So, Mo and Ko and their correlations with porosity, permeability, pore throat radius and thermal evolution degree were investigated. The critical values of So, Mo and Ko that define HADL were quantified to be So = 0, Mo = 0 and Ko = 100. Our study indicates that the HADL in petroliferous basins varies from less than 3,000 m to more than 13,000 m deep, depending on the hydrocarbon composition, reservoir lithology, reservoir age, geothermal gradient, tectonic movement, etc. Two factors play an essential role in the formation and variation of HADL: 1) the depletion of hydrocarbon generation potential of source rocks which cuts off hydrocarbon contribution for reservoirs formation and 2) the termination of differential compaction which eliminates capillary pressure difference between the outer surrounding rocks and inner reservoir layers, ending the dominant driven force for hydrocarbon migration and accumulation in deep and tight reservoir layers. All proven oil reserves of 33.95 billion tons equivalent in China, as well as world’s discovered 52,926 oil and gas reservoirs and their unproved potential resources, are distributed above the HADL we defined.

Mixing characteristics and energy conversion in the coalescence process of the two droplets

In the case of fluid flow with a low Reynolds number, the internal fluid stratification can be easily observed after droplet coalescence, impeding rapid mixing of fluid. In this study, the capillary pressure difference is increased by adjusting the droplet size and the interfacial tension, so that a strong jet can be generated, resulting in a rapid mixing. Five distinct droplet mixing modes have been found. The phase diagram of the droplet mixing modes is obtained and the transition rule of the droplet mixing modes is established on this basis. A novel energy distribution model is employed to analyze the dependence between liquid bridge expansion and jet movement of two droplets. In addition, a criterion for evaluating the mixing efficiency of droplets is presented. The results presented in this paper provide a theoretical basis and practical guidance for realizing the efficient mixing of microfluids.

Identification of the best correlations of permeability anisotropy for Mishrif reservoir in West Qurna/1 oil Field, Southern Iraq

At present, reservoir whether isotropy or anisotropy is taking more attention, particularly the difference in (porosity, permeability, and capillary pressure) associated with pore space. These differences are due to the original sediments and thus diagenetic changes. It has been found that common models are insufficient to predict reservoir performance and field management program design. Recovery factor (RF) is the main factor affecting the optimization process for any reservoir that is very sensitive to reservoir heterogeneity and hence an accurate vertical and horizontal permeability (Kv and Kh) distribution is required. A case study is represented in this paper aimed at vertical permeability estimation from horizontal permeability and porosity for Mishrif reservoir in west Qurna/1 oil field southern Iraq. This study has been accomplished by testing five models, harmonic averaging, Kozeny-Carman equation, Zahaf and Tiab, Iheanacho et al., and Fazelalav to determine vertical permeability and comparing the results with core data values. It is found that the models were used showed an accuracy variation between the units of Mishrif reservoir based on Mishrif full diameter cores from 20 wells. Four new correlations are obtained for mA, CRII, mB1, and mB2 units for Mishrif Reservoir in West Qurna/1 oil field. The correlation shows that the permeability is depending on porosity in the mA unit due to the homogeneity and the Mb1 unit has a higher anisotropy than the other units.

Reusable Capillary Flow-Based Wax Switch Valve for Centrifugal Microfluidics

Introduction: This paper presents a new repeatable Open-Close switch valve (SV) for the CD microfluidic platforms. The SV is designed by using a combination of controlled phase change and capillary flow of Ferrowax. The phase change of the wax is controlled using a laser. When the wax is illuminated with a laser, the energy of the laser is absorbed by the Ferro particles embedded inside the wax, causing the wax to melt. The melted wax can spontaneously wick through capillary channels due to its low contact angle. The Open-Close nature of the valve is attained by rationally designing the capillary flow path of the wax. The capillary flow path design is such a way that the melted wax is directed to the open fluidic path (Normally open configuration) to block the channel (Close configuration). The reversal of the blocking is achieved by remelting the wax and driving it to the overflow chamber downstream. A unique wax flow path is also designed to enhance the capillary flow and the response time of the valve. Background: Centrifugal platform-based CD fluidics has created a new paradigm of inexpensive point-of-care diagnostics[1]. It is now widely used in applications like polymerase chain reaction assays, blood plasma separation, etc.[2,3] Since CD fluidics has presented an innovation in point-of-care diagnostics, it is essential to have a proper valving system for reliable opening/closing of the channels. Currently, there are two main types of valves in the CD platform: laser valves and z-axis wax valves. Both of these valves are good for one-time use only and have complex fabrication routes. Therefore, there is a need for simple, reusable SV in CD fluidic platforms. Theory: The capillary pressure drives the capillary flow in a channel. The capillary pressure difference between atmosphere and the liquid meniscus inside a rectangular microchannel (Pc) is given by Young-Laplace’s equation:-Pc = 2γ(cosθ)(1/w+1/h) (1)where γ is the surface tension, θ is the contact angle with the channel material, w is the width of the channel, and h is the height of the channel. In this design, the resistance offered by the trailing liquid is given by the equation:Rhyd = 12μL/(h3w*(1-0.63(h/w)) (2)For capillary flow, the flow rate (Q) can be obtained byQ = wh(dL/dt) = -Pc/Rhyd (3)For a shallow channel (h<<w), we can neglect the terms containing 1/w, giving the following simplified equation for the flow velocitydL/dt = γ(cosθ)h/(6μL) (4)Upon integration, the fluid length at an instant t is obtainedL = √(γht(cosθ)/3μ) = W√t (5)where W is the Washburn’s constant. We use a new channel design and a flexible adhesive film, and the modified channel shows significant improvement in the capillary flow velocity. A modified empirical model capturing this effect is currently being developed. Materials and Method: The channels and the chambers are milled on an acrylic sheet of thickness 3 mm using Tormac PCNC CNC milling machine (Fig 1a). The Ferro-wax is prepared by mixing Sigma Aldrich Paraffin wax (MP 53 - 37oC) with Ferrofluid (Ferrotec EFHI 60 cc) at the ratio of 2:1 and stirring the mixture at 65oC for 12 hours. The mixture is brought down to room temperature and placed inside the designated chamber. Then, the CD is laminated using a single side pressure-sensitive adhesive (Fig 1a). To achieve Close configuration (Fig 1b), the wax inside the CD is heated up for 5 minutes at 65oC. The melted wax flows to the reagent flow path and solidifies to block the channel. Remelting the wax and directing the melted wax to the overflow chamber brings the valve back to the Open configuration (Fig 1b). The unique channel edges for enhanced capillary flow are fabricated by applying two layers of tape (Fig 1a). Experimental Results:- Experimental characterization of SV was performed by fabricating channels having cross-section areas ranging from 0.05 to 0.625 mm2. A 2.32 W laser placed at a distance of 3 mm from the top surface of the CD is used for heating the Ferrowax. The Normally Close configuration (Fig 1b) is achieved by heating the wax inlet chamber for 5 minutes at 65oC. The wax is driven to the reagent channel by moving along the edge gaps of the wax chamber. The solidified wax prevents the fluid from moving downstream. The sequential release of the reagent is achieved using SV as shown (Fig 1c, 5). A ‘teeth’ design is used at the bottom of the wax inlet to avoid bubble formation inside the chamber. This teeth design also ensures a large number of Open-Close operations for a given amount of wax. Finally, we demonstrate the fidelity of the SV closure (Close configuration) on the CD platform on upwards of 7000 RPM. A parametric study of the air gap is being carried out to determine an optimized design for a faster response.

Role of trapped liquid in flow boiling inside micro-porous structures: pore-scale visualization and heat transfer enhancement

Flow boiling is an important heat dissipation method for cooling high heat flux surfaces in many industrial applications. The heat transfer can be further enhanced by using porous media surfaces due to their high specific surface areas. However, although flow boiling in channels is well understood, the phase-change behavior with the additional capillary effect induced by the porous structures is not well understood, and the design of the porous structures is difficult to avoid dryout and over-temperature accidents. A pore-scale lab-on-a-chip method was used here to investigate the flow boiling heat transfer characteristics inside micro-porous structures. The flow patterns, captured in the two-phase region with a uniform pore-throat size of 30 μm, showed that liquid was trapped in the pore-throat structures as both dispersed liquid bridges and liquid films. Moreover, the liquid film was shown to be moving on the wet solid surface by laser-induced fluorescence and particle tracking. A theoretical analysis showed that the capillary pressure difference between adjacent liquid bridges could drive the liquid film flows, which helped maintain the coolant supply in the two-phase region. The pore-throat parameters could be designed to enhance the capillary pressure difference with multiple throat sizes of 10 – 90 μm which would enhance the heat transfer 5% – 10% with a 5% – 23% pressure drop reduction. This research provides another method for improving the flow boiling heat transfer through the porous structure design besides changing the surface wettability.

Measurement of the Hygric Resistance of Concrete Blocks with Perfect Contact Interface: Influence of the Contact Area

Introduction: Concrete sealing blocks are not only used in Brazil but worldwide. T he knowledge of the material properties in the presence of moisture becomes necessary to study the durability of buildings. Methods: An experimental study was carried out in order to analyse the effect of contact area on the capillary absorption coefficient of concrete samples used in sealing blocks, according to several standards: NBR 9779 (2012), EN 1015-18 (2002), ISO 15148 (2002) and ASTM C1794 (2015). Two types of specimens were analysed; monolithic samples and samples with a perfect contact interface. The monolithic samples were also subjected to axial and radial compression in order to enhance the capacity of masonry. Results: The experimental results for the samples with perfect contact interface indicate that the water absorption before the interface presents similar behaviour to the monolithic samples. However, it is possible to observe a reduction of the absorption rate when water reaches the interface due to the hygric resistance. In other words, the moisture transport is significantly retarded by the existence of an interface, i.e., the discontinuity of moisture content across the interface indicated that there was a difference in capillary pressure across the interface. Also, the interface contact area does not greatly influence the water-resistance values. Conclusion: Finally, the Hygric Resistance values (HR), in multilayer building components, with perfect contact interface are calculated using the “knee point” methodology.

Dynamic analysis of deformation and start-up process of residual-oil droplet on wall under shear flow

This study focuses on the dynamic process of deformation and start-up of an oil droplet on a wall driven by an external shear flow. A mesoscopic numerical method is developed based on the lattice Boltzmann framework for multiphase coupled with the color-gradient model. After validations of the numerical method, we performed force analyses based on the flow field, considering the pressure difference and the shear stress inside the droplet simultaneously. It was intriguing to find that the shear stress is a driving force instead of a resistance due to the interesting phenomenon that a vortex was formed inside the droplet and the direction of reaction shear stress acted by solid wall accorded with the direction of the start-up. A force-balance model was established on the basis of the force analyses to predict the yield criteria in terms of the critical capillary number and pressure difference. Finally, by comparing the flow field before and after the start-up of the droplet, it was found that the proportion of the wall applying shear driving force decreases but the values of the shear stress increase significantly after the start-up compared to before the start-up.

Capillary pressure in the anisotropy of sediments with hydrate formation

The random nucleation and growth of hydrates in the pore space contribute to the heterogeneity of hydrate sediments, which results in anisotropic fluid flow. An exact forecast for capillary pressure in different directions, which governs the gas/water distribution and the volume of residual water saturation in porous sediments, is of significant importance for hydrate exploitation. In this study, the index properties of the artificial hydrate sediment were characterized through X-ray computed tomography (CT) visualization scanning. The spatial structure feature of hydrate sediment was captured via a topological pore network, which was established from CT imaging. Then, the evolution of capillary pressure in anisotropy with the formation of hydrates was simulated and discussed. The results indicated that with hydrate formation, the capillary pressure curves became steeper, representing skewness with finer slanting degrees and poor sorting. Moreover, the differences in capillary pressure with the same hydrate saturation between different directions was enlarged. Stronger capillary heterogeneity in the vertical direction represents greater heterogeneity, according to the Leverett J-Function.

Abstract 16026: Invasive Hemodynamic Assessment of Patients With Heart Failure With Preserved Ejection Fraction With Anemia and Iron Deficiency

Introduction: Anemia is associated with increased mortality, cardiovascular events, and decreased quality of life in patients with heart failure with preserved ejection fraction (HFpEF). Iron deficiency may contribute to disease severity independent of effects on red cell mass. The hemodynamic consequences of anemia and iron deficiency in HFpEF remain unclear. Methods: We analyzed a cohort of 313 consecutive subjects with HFpEF diagnosed by invasive hemodynamic assessment, and compared echocardiographic and hemodynamic characteristics of anemic versus non-anemic subjects. Anemia was defined as hemoglobin &lt;13 g/dL in men and &lt;12 g/dL in women. Iron deficiency was defined as ferritin &lt;100 ug/L. Results: Compared to patients without anemia, HFpEF patients with anemia displayed higher NT-proBNP, elevated pulmonary artery (PA) pressures at rest and at peak exercise, and lower oxygen consumption at peak exercise (Table). There was no difference in pulmonary capillary wedge pressure (PCWP). Patients with iron deficiency were more likely to be women. At rest, patients with iron deficiency displayed lower left ventricular (LV) mass, higher resting SVRI and lower cardiac index (CI), but there were not significant differences with exercise. Conclusions: Anemia in HFpEF is associated with greater evidence of congestion and more severe pulmonary hypertension, contributing to reduced exercise capacity. Iron deficiency in HFpEF is more common in women and associated with lower cardiac output at rest, but hemodynamics are otherwise similar. Further study is required to understand the mechanisms by which anemia and iron deficiency influence cardiac function and outcomes in HFpEF.

Self-assembled nanoparticle-coated interfaces: Capillary pressure, shell formation and buckling

HypothesisParticle accumulation at liquid-liquid or liquid-gas interfaces can significantly alter capillary behavior and give rise to unusual interfacial phenomena including the asymmetric macroscopic mechanical response of the interface. ExperimentsThis study explores the accumulation of cetyltrimethylammonium bromide-modified nanoparticles at fluid interfaces and the subsequent mechanical response of nanoparticle-coated droplets during contraction and expansion. Droplet tests involve the simultaneous recording of the droplet shape and the capillary pressure. Complementary single-pore experiments examine the response of particle-coated interfaces as they traverse a pore constriction. FindingsInterfaces promote order. The time-dependent nanoparticle accumulation at the interface is diffusion-controlled. The nanoparticle coated droplets can sustain negative capillary pressure before they buckle. Buckling patterns strongly depend on the boundary conditions: non-slip boundary conditions lead to crumples while slip boundary conditions result in just a few depressions. The particle-coated interface exhibits asymmetric behavior in response to particle-level capillary forces: an “oil droplet in a nanofluid bath” withstands a significantly higher capillary pressure difference than a “nanofluid droplet in an oil bath”. A first-order equilibrium analysis of interaction forces explains the asymmetric response. Single-constriction experiments show that the formation of particle-coated interfaces has a pronounced effect on fluid displacement in porous media.

Numerical simulation on natural gas migration and accumulation in sweet spots of tight reservoir

Although the exploration and development of tight gas have made great progress, the quantified study on gas migration and accumulation in sweet spots of tight gas reservoir is still limited. In this work, a computer program is developed to conveniently describe the different shape of sweet spots and the fractures in tight reservoir. Then, gas migration and accumulation processes are simulated, and the numerical simulation results are visualized and quantified. Based on the simulation results, the mechanism of gas migration and accumulation in sweet spots is revealed. The results indicate that the migration and accumulation of gas are two relatively independent processes. The gas migration process is determined by the permeability of rocks. The critical condition of gas accumulation in sweet spots is mostly determined by the capillary pressure difference between sweet spots and surrounding rock. The two migration patterns are clearly observed during the numerical simulations. When surrounding rock has seepage capacity for gas, the migration pattern tends to be piston-like displacement; when surrounding rock is impermeable for gas, the gas can only migrate into sweet spots through connected fractures. As a result, the migration pattern for this situation tends to be fingering displacement.

Effects of petroleum retention and migration within the Triassic Chang 7 Member of the Ordos Basin, China

The effects of petroleum retention within and expulsion from five intervals within the Triassic Chang 7 Member in the Ordos Basin in China have been demonstrated by deciphering a large suite of petrologic, organic petrographic, and organic geochemical analyses on 106 core samples.Organic properties and lithological heterogeneities control the amount and chemical composition of retained petroleum. Enrichment of aliphatic hydrocarbons in the silty, organic-lean intervals versus enrichment of aromatic fluids in the clayey, organic-rich units are probably caused by compositional fractionation occurred during primary and short-distance secondary migration. Migration of excess petroleum from organic-rich units to those organic-lean counterparts was further corroborated by the negative expulsion efficiencies calculated using a mass-balance model in the organic-lean intervals. Capillary pressure difference induced by the contrast in pore throat size of the clayey, organic-rich versus the silty, organic-lean intervals is postulated to be the major driver for the migration.A significant implication of this study is that the hydrocarbons in the first and fourth intervals constitute potential petroleum exploitation targets, given (i) improved oil quality caused by enriched aliphatic compounds versus viscous aromatic and polar compounds, (ii) lower organic matter sorption affinities, (iii) relatively high contents of brittle minerals in these two intervals. Despite its high content of retained hydrocarbons, the organic-rich fifth interval is not the best target, which is mainly due to the high sorption affinity of the organic matter structure, thereby causing low oil mobility and producibility.

Natural Gas Reservoir Characteristics and Non-Darcy Flow in Low-Permeability Sandstone Reservoir of Sulige Gas Field, Ordos Basin

In order to reveal the gas–water distribution and formation mechanism of the low-permeability sandstone gas reservoir, the gas reservoir distribution and the formation mechanism in a low-permeability sandstone gas reservoir are investigated using data obtained from a physical simulation experiment of gas percolation. The exploration and experimenting for petroleum in the upper Paleozoic gas pool of the Sulige gas field in the Ordos basin in this paper. Results showed that the gas reservoir is characterized by low gas saturation, a complex distribution relationship of gas–water, and weak gas–water gravity differentiation. The characteristics of gas distribution are closely related to permeability, gas flow, and migration force. The capillary pressure difference is the main driving force of gas accumulation. There exists a threshold pressure gradient as gas flows in low-permeability sandstone. The lower that permeability, the greater the threshold pressure gradient. When the driving force cannot overcome the threshold pressure (minimal resistance), the main means of gas migration is diffusion; when the driving force is between minimal and maximal resistance, gas migrates with non-Darcy flow; when the driving force is greater than maximal resistance, gas migrates with Darcy flow. The complex gas migration way leads to complicated gas- water distribution relationship. With the same driving force, gas saturation increases with the improvement of permeability, thus when permeability is greater than 0.15 × 10−3 µ m2, gas saturation could be greater than 50%.