Moran Wang

Tsinghua University | TH · Department of Engineering Mechanics

Hydraulic fracturing is widely used to stimulate unconventional reservoirs, but a systematic and comprehensive investigation into the hydraulic fracturing process is rare. In this work, a discrete element-lattice Boltzmann method is implemented to simulate the hydro-mechanical behavior in a hydraulic fracturing process. Different influential factor...

In recent years, the rapid development of micro/nanosystems raises the demand of thermal optimization of the new designs, and thus the accurate and efficient prediction of phonon transport in mesoscopic systems with complex interfaces is required. This work proposes a hybrid Monte Carlo-discrete ordinates method (MC-DOM) for steady-state phonon tra...

Surface charging at immiscible liquid-liquid interface is essential to the emulsion stability, surfactant adsorption, and various engineering applications such as drug delivery and mineral flotation. However, droplet electrophoresis, as a widely-used electrokinetic method to measure the surface charge density, has various limitations in physical mo...

Thermal transport across the interface between metals and semiconductors is ubiquitous in micro- and nano-manufacturing devices. The direct simulation of thermal transport in such multilayers is rarely studied due to different main carriers involved, such as electrons in metals and phonons in semiconductors. This study investigates thermal transpor...

The pore network is an approximate representation of the void space of porous materials, such as rocks and soil, via pores (corresponding to large cavities) and throats (narrow constrictions). During extraction of networks from real void space, ambiguous definitions or determinations of pores and throats may cause significant errors in the predicti...

We utilize a pixel-based fracture detection algorithm to digitize 80 published outcrop maps of different scales at different locations. The key fracture properties, including fracture lengths, orientations, intensities, topological structures, clusters, and flow, are analyzed. Our findings provide significant justifications for statistical distribu...

Multiphase displacement in porous media can be adjusted by micro/nanoparticle suspensions, which is widespread in many scientific and industrial contexts. Direct visualization of suspension flow dynamics and corresponding multiphase patterns is crucial to understanding displacement mechanisms and eventually optimizing these processes in geological,...

Agglomeration, adsorption, and extraction in dispersed multiphase systems are ubiquitously encountered in biological systems, energy industry, and medical science. In this work, a novel lattice model is extended to the three-component complex systems and criterions based on the determinant \Delta_i=F_i-K_c,i are accordingly proposed to predict the...

We study the preference of two-phase displacements systematically by theoretical derivations and numerical simulations via a non-uniform pore doublet model. All the most important impact factors, including viscosity ratio, capillary number, wetting conditions and boundary conditions, have been considered, and finally a complete phase diagram for pr...

Digital rock analysis provides us a powerful tool for predicting geophysical properties and studying fluid and interfacial transport mechanisms in rocks. However, people have to struggle and find a balance between scanning resolution and sample size due to current limitations of imaging technologies. With satisfaction of resolution requirement, the...

Systematic analysis on the complexity of fracture systems, especially for three-dimensional (3D) fracture networks, is largely insufficient. In this work, we generate different fracture networks with various geometries with a stochastic discrete fracture network method. The fractal dimension (D) and the singularity variation in a multifractal spect...

We report a theoretical investigation of coherent-to-incoherent heat conduction in multilayer nanostructures. In the coherent regime where the phonon motion is quasi-harmonic, the elastic continuum model gives accurate cross-plane thermal conductivity predictions of upper limits and demonstrates that the coherent transport is the result of the inte...

Stimulated reservoir volume (SRV), the highly permeable fracture network created by hydraulic fracturing, is essential for fluid production from low-permeable reservoirs. However, the configuration of SRV and its impacting factors are largely unknown. In this work, we adopt the stochastic discrete fracture network method to mimic natural fractures...

Accurate assessment of the formation rock permeability and porosity is crucial for geotechnical applications. For tight formation rocks, separate measurements of permeability and porosity result in high time costs and degraded accuracy. This contribution presents an improved straight-line method that allows simultaneous permeability and porosity de...

Hypothesis: Preferential flow in porous media is commonly encountered and decreases the multiphase displacement efficiency. Here, we synthesized microgel-in-oil in suspension and demonstrated that microgel-in-oil as a novel additive could present self-adaptive transport behavior and introduce a novel multiphase displacement mode for improving displ...

We report non-monotonic wettability effects on displacement efficiency in heterogeneous porous structures at the post-breakthrough stage, in contrast to the monotonic ones in homogeneous porous structures. Experiments on designed microfluidic chips show that there exists a critical wettability to attain the highest efficiency of displacement in the...

Strong heterogeneity, low matrix permeability, and complex oil–water interaction make the fluid flow in carbonate rocks extremely complicated. In this study, we quantitatively characterize and simulate single-phase and multiphase flows with multiscale pore–vug–fracture structures involved in the carbonate reservoir developments. The main studies an...

A steady-state Monte Carlo scheme is developed for phonon transport based on the energy-based deviational phonon Boltzmann transport equation (PBTE). Other than tracking trajectories and time evolution of each packet in the transient methods, this steady-state method determines the paths of energy packet from being emitted to the steady state throu...

T-type intersections are commonly observed in natural fracture networks. Their impacts on the connectivity and flow results in complex fracture networks are rarely investigated. In this work, we implement the discrete fracture network method to construct complex fracture networks, denoted as original fracture networks. By implementing the rule-base...

Fractures and their connectivity are essential for fluid flow in low permeability formations. Geological outcrops can only provide two-dimensional (2D) information, but subsurface fractures are three-dimensional (3D). The percolation status of 3D fracture networks and their 2D cross-section maps are rarely investigated simultaneously. In this work,...

Understanding of thermal effects on ion transport in porous media is very important for environmental applications. The movement of ions along a temperature gradient is named thermophoresis or thermodiffusion. In nanoporous media, where the interaction of ions with solid-liquid interfaces has a significant influence on their migration, the theoreti...

We investigate the impact of wettability distribution, pore size distribution and pore geometry on the statistical behaviour of trapping in pore-throat networks during capillary displacement. Through theoretical analyses and numerical simulations, we propose and prove that the trapping patterns, defined as the percentage and distribution of trapped...

Preferential flow is commonly encountered but decreases the efficiency of multiphase displacement in most industrial processes. Microgel particle suspensions with polymer/colloid duality are a potential candidate to overcome such nonuniform flow. In this study, a novel mechanism of preferential flow control in heterogeneous porous media by concentr...

The fractal dimension and multifractal spectrum are widely used to characterize the complexity of natural fractures. However, systematic investigations, considering impacts of different fracture geometrical properties (fracture lengths, orientations, center positions) and system sizes, on the fractal and multifractal characterization of complex fra...

Interfacial roughness plays an important role in nanoscale thermal transport, while this issue still lacks a theoretical description due to the difficulty in quantifying the phonon sacttering at the disordered interface. We report an elastic wave model (EWM) that describes the phonon-interface interaction by the interface elasticity. The transmissi...

This contribution presents an early‐time solution for permeability evaluation in pulse‐decay tests. A nonlinear governing equation for gas transport in the sample is derived considering the pressure dependence of gas compressibility and Klinkenberg slippage effect, and the early‐time solution is obtained through the integral balance analysis. The p...

Mobilization of trapped ganglia is of fundamental importance in two-phase displacement. Wettability alteration could be an effective approach to mobilizing ganglia, yet its feasibility as well as the impact of wettability in general lacks study. We investigate the wettability effects on trapped ganglia by theoretical analysis and numerical simulati...

Fractures and their connectivity are essential for fluid flow in low permeability formations. Abundant outcrops can only provide two-dimensional (2D) information, but subsurface fractures are three-dimensional (3D). The percolation status of 3D fracture networks and their 2D cross-section maps are rarely investigated simultaneously. In this work, w...

Electron transport in ultraclean two-dimensional materials has received much attention. However, the sign of the magnetoresistance effect in various electron flow regimes remains controversial. In this work, the complete electron Boltzmann transport equation is numerically solved with the discrete ordinate method in the real space to clarify the co...

Wettability alteration has been recognized as the dominant mechanism of ion-tuned waterflooding, where the ionic composition of injecting brine is modified to improve oil recovery. Yet mechanisms of ion-tuned wettability have not been fully understood, and there are ongoing debates over the effectiveness and relative contribution of each mechanism....

Permeability and porosity are the two most important parameters of rocks for the evaluation and exploitation of oil/gas reservoirs. In this study, a modified pulse‐decay method has been developed to measure both permeability and porosity simultaneously. In the present method, the gas pressure in one chamber is changed (increased or decreased) insta...

This work studies the in-plane phonon transport through double-layer, superlattice, and four-layer thin films by theoretical analyses and Monte Carlo simulations. The spectral diffuse mismatch model and the adiabatic diffuse scattering are taken as the interface and surface boundary conditions respectively. The results indicate that the number of t...

Prediction of oil and gas production is an important way to determine its development economy. However, at present the production prediction is still hard to achieve consistency between the physics-based method and the data-based method. For shale oil and gas production analysis, in-depth combination of mathematical advantages brought by BP neural...

The understanding of hydrodynamic heat transport in finite-sized graphitic materials remains elusive due to the lack of an efficient methodology. In this paper, we develop a computational framework enabling an accurate description of heat transport in anisotropic graphite ribbons by a kinetic theory approach with full quantum mechanical first-princ...

Transport mechanisms of small droplets on walls in micropores become significant for applications in energy, resource and biomedical engineering, however, a suitable numerical tool remains challenging. Macroscopic approach is ideal both in computing cost and simplicity but its applicability is doubted for nanoscale droplet, yet no clear evaluation...

The electron-phonon (e-ph) coupling process in ultrafast dynamics involves non-equilibrium effects including non-thermalized electrons and temporal non-equilibrium between different phonon branches. During such process, the two-temperature model (TTM) is employed to extract the relevant e-ph coupling constant though experiments themselves have demo...

Diverse ionic current rectification methods for nanofluidic chips have recently emerged. Herein, we theoretically demonstrate that by applying a temperature gradient to the aqueous solution, the ionic rectification property of a tapered nanochannel can be manipulated by applying temperature gradients from the tip to base and vice versa. Our modelin...

In this work, a lattice Boltzmann scheme is developed for numerical solution of the phonon Boltzmann equation under Callaway's dual relaxation model in the hydrodynamic limit. Through a Chapman-Enskog expansion to the lattice Boltzmann equation with the resistive scattering term as an equivalent source term, we recover a phonon hydrodynamic equatio...

The pulse-decay method is one of the most widely used transient methods for permeability measurements. Though many modified pulse-decay methods with various experimental designs have been proposed, the theoretical analysis is still insufficient, especially from the perspective of the boundary and initial conditions. In terms of boundary conditions,...

Spontaneous imbibition (SI) of the injected fluid into the pore space of a tight oil reservoir and replacing the crude oil therein has been considered as one of the possible mechanisms in increasing oil recovery. Such deeply buried reservoir rocks is usually under high-pressure and high-temperature conditions. Besides, their interior porous structu...

To improve the understanding of gas transport processes in tight rocks (e.g., shales), systematic flow tests with different gases were conducted on artificial micro- to nanoporous analogue materials. Due to the rigidity of these systems, fluid-dynamic effects could be studied at elevated pressures without interference of poro-elastic effects. Flow...

Understanding of the energy exchange between electrons and phonons in metals is important for micro- and nanomanufacturing and system design. The electron-phonon (e−ph) coupling constant describes such exchange strength, yet its variation remains still unclear at micro- and nanoscale where the nonequilibrium effects are significant. In this work, a...

Non-Newtonian fluids may cause nonlinear seepage even for a single-phase flow. Through digital rock technologies, the upscaling of this non-Darcy flow can be studied; however, the requirements for scanning resolution and sample size need to be clarified very carefully. This work focuses on Bingham fluid flow in tight porous media by a pore-scale si...

In this work, we study thermal phonon vortex in graphene ribbon by a discrete-ordinate solution of phonon Boltzmann equation under Callaway's dual relaxation model. The phonon scattering rates of normal and resistive processes are acquired from ab initio calculation without need of any empirical input parameters. The temperature, size and isotope e...

Particles motion through a fluid-fluid interface is of both academic and industrial interests, yet, underlying mechanisms have not been fully understood. In this work, a two-phase LBM-DEM coupling model is developed to systematically explore the behavior of a particle moving through an immiscible fluid-fluid interface under different physical condi...

Preferential flow that leads to non-uniform displacement, especially in heterogeneous porous media, is usually unwelcome in most practical processes. We propose a self-adaptive preferential flow control mechanism by using dispersed polymers, which is supported strongly by experimental and numerical evidence. Our experiments are performed on a micro...

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...

Electroosmotic flow (EOF), a consequence of an imposed electric field onto an electrolyte solution in the tangential direction of a charged surface, has emerged as an important phenomenon in electrokinetic transport at the micro/nano‐scale. Because of their ability to efficiently pump liquids in miniaturized systems without incorporating any mechan...

Understanding of the energy exchange between electrons and phonons in metals is important for micro- and nano-manufacturing and system design. The electron-phonon (e-ph) coupling constant is to describe such exchange strength, yet its variation remains still unclear at micro- and nanoscale where the non-equilibrium effects are significant. In this...

In this work, a lattice Boltzmann scheme is developed for numerical solution of the phonon Boltzmann equation under Callaway's dual relaxation model in the hydrodynamic limit. Through a Chapman-Enskog expansion to the lattice Boltzmann equation with the resistive scattering term as an equivalent source term, we recover a phonon hydrodynamic equatio...

Plain Language Summary Hydro‐fracturing is an important technique in petroleum industry to stimulate well production. Generally, it is believed that lower viscosity fluids will create more complex fractures with higher cost. The mechanism of induced more complex fracture is still not fully understood yet, which may result in uncertain expense on fl...

Many important applications in the food industry, biological systems, and recovery of fluids from the subsurface involve multiphase flow dynamics where one of the phases is a non-Newtonian, viscoelastic fluid. In this work, we investigate the role of viscoelas-tic displacing fluids in recovering trapped nonwetting fluids. We perform the lattice Bol...

Particles suspension is considerably prevalent in petroleum industry and chemical engineering. The efficient and accurate simulation of such a process is always a challenge for both the traditional computational fluid dynamics (CFD) and lattice Boltzmann method (LBM). Immersed moving boundary (IMB) method is promising to resolve this issue by intro...

Purpose The purpose of this paper is to investigate the evolution of the permeability of spherical packing during cold compaction by pore-scale modeling. Design/methodology/approach The discrete element method (DEM) is used to generate spherical packing structure under different compressive pressures and the Lattice Boltzmann method (LBM) is adopt...

Low salinity waterflooding (LSW) has attracted attention of numerous researchers as a promising technique for enhanced oil recovery, yet its application is still limited because of incomplete mechanisms and unreliable predictions. This paper summarizes relevant mechanisms for predicting responses of LSW. Since the wettability alteration is generall...

Despite the significant influence of solution temperature on the structure of electrical double layer, the lack of theoretical model intercepts us to explain and predict the interesting experimental observations. In this work, we study the structure of electrical double layer as a function of thermo‐chemical properties of the solution by proposing...

Interfacial phonon transport through thin films with heat source exists widely in devices, such as electronics and thermoelectrics, yet the mechanism is still unclear. In this work, thin films made of bi-material pairs with heat sources are simulated by a developed Monte Carlo method, namely kinetic-type Monte Carlo method. The size effects of the...

Commercial-scale photoelectrochemical (PEC) water splitting devices have been proved to be cost-competitive with fossil-based fuels. Nevertheless, large-scale PEC water splitting cells with high performance are not-yet to be demonstrated, and...

Micro‐gel particle suspensions (MGPS) have been proposed for enhanced oil recovery (EOR) in reservoirs with harsh conditions in recent years, yet the mechanisms are still not clear because of the complex property of MGPS and the complex geometry of rocks. In this paper, the micro‐gel particle‐based flooding has been studied by our microfluidic expe...

The direct simulation of the dynamics of second sound in graphitic materials remains a challenging task due to lack of methodology for solving the phonon Boltzmann equation in such a stiff hydrodynamic regime. In this work we aim to tackle this challenge by developing a multiscale numerical scheme for the transient phonon Boltzmann equation under C...

Previous work on solute transport with sorption in Poiseuille flow has reached contradictory conclusions. Some have concluded that sorption increases mean solute transport velocity and decreases dispersion relative to a tracer, while others have concluded the opposite. Here we resolve this contradiction by deriving a series solution for the transie...

The thermal conduction through interfaces plays an important role for optimization and new designs in micro/nano energy system. However, the available knowledge and understanding on the physical picture of phonon transport at interfaces are still insufficient. The discrete-ordinates method (DOM) has been recently applied to solve the equation of ph...

Based on the mesoscopic Boltzmann equation of two-dimensional electrons, we develop both a new numerical algorithm named Discrete Ordinate Method (DOM) to solve the mesoscopic equation and a new macroscopic hydrodynamic model for electron transport in the diffusive regime at low temperatures. It lays a foundation for the subsequent theoretical work...