Xiaobing Lu

• Vietnam Academy of Science and Technology

The stability of gas hydrate (GH) dissociation is crucial for understanding and predicting various hazards triggered by GH dissociation, such as landslides and gas blowouts. This study employs linear stability analysis and numerical simulation approaches to investigate the dynamics of GH dissociation under depressurization and heating. An instabili...

Layered hydrates are widely distributed in marine sediments and it has a significant effect on the mechanical properties of hydrate-bearing sediment (HBS) strata. Nevertheless, the mechanical properties of layered HBS remain poorly understood, which is related to the safety and stability of mining. In this paper, triaxial tests were conducted to in...

Vertical pipe hydraulic conveying is currently considered the most promising method for deep-sea mining. The conveying velocity at the inlet of the vertical pipe is often close to a pulsating form due to the influence of the flexible pipe and the marine environment. This study employs a combined Computational Fluid Dynamics (CFD) and Discrete Eleme...

Compressible particle-laden systems are widely present in various natural phenomena and engineering applications. This study focuses on developing a compressible semi-resolved computational fluid dynamics-discrete element method (CFD-DEM) coupling model with heat transfer. The model can simulate gas–solid and liquid–solid systems across a range of...

This paper presents a numerical investigation of the hydraulic conveying performance of coarse particles with the inlet pulsating fluid velocity in a vertical pipe. The influence of pulsating parameters, in terms of pulsating amplitudes and frequencies, on hydraulic conveying is mainly considered. The pulsations of particle and slip velocity are as...

In this paper, we investigate the concentration instabilities that arise in vertical dense particulate flows during hydraulic conveying. The widely used two-fluid model for dense particulate flows is employed, and existing closure relations for drag correlation, stress tensors, etc., found in the literature are utilized. The ratio between the pipe...

The Eulerian-Lagrangian approach is commonly employed in particulate flows, which can be classified into two subcategories: unresolved computational fluid dynamics-discrete element method (CFD-DEM) and resolved CFD-DEM. When the particle sizes are comparable to the cell sizes, the interphase coupling is not straightforward anymore and both the conv...

Calculation of particle volume fraction in computational fluid dynamics-discrete element method simulation of particulate flows with coarse particles ABSTRACT Computational fluid dynamics-discrete element method is frequently used for modeling particulate flows due to its high efficiency and satisfactory accuracy. The particle volume fraction is a...

This paper presents a numerical simulation for dense particulate flows with coarse particles in inclined pipe to identify different flow regimes by means of computational fluid dynamics-discrete element method. The drag, gravitational, pressure gradient and virtual mass forces on particles, as well as the effect of particle-particle collisions are...

In this work, a semi-resolved computational fluid dynamics-discrete element method is employed to study the effects of fluid-particle and particle-particle/wall interactions on particle mixing and segregation behaviors and particle dynamics with different particle sizes in a vertical pipe. There are two species of particles with the same density in...

A separate-bottom Couette cell is used to carry out ring-shear tests on sand and hydrate, and the evolution of shear bands is recognized using the tracer method. Based on experimental verification, a numerical simulation method is applied to study the shear band variation law with the height and strength of the sample. Analyzing the distribution of...

Solid–liquid two-phase flow with dense coarse particles in the pipeline exists widely in energy and resources engineering, especially in the prospective hydraulic lifting scenario of deep-sea mining. In this paper, the coarse particles' transportation behavior in a vertical pipe is investigated based on an optimized Eulerian–Lagrangian method propo...

The solid–liquid two-phase flow with coarse particles is ubiquitous in natural phenomena and engineering practice, which is characterized by coarse particles, high particle concentration, and large particle size distribution. In this work, the numerical models describing two-phase flows are reviewed, which given that the Eulerian–Lagrangian method...

The occurrence of a shear band is often thought as the precursor of failure. To study the initiation of shear banding in gas hydrate-bearing sediments, two groups of triaxial compression tests combined with a CT (computer tomography) scan were conducted by triaxial CT-integrated equipment under two confining pressures and seven hydrate saturations....

A series of experiments were conducted to investigate flow pattern transitions and concentration distribution during simultaneous pipe flow of oil–water two-phase flow through the horizontal and vertical sections. The flowing media applied were white mineral oil and distilled water. Superficial oil and water velocities were between 0 and 0.57 m/s....

It is essential to understand the in-situ geomechanical properties of natural gas hydrate-bearing reservoirs for hydrate drilling, the design of reservoir stimulation and production schemes, geologic disaster prevention, and environmental impact assessment. In this way, it serves as the basis for the development and utilization of gas hydrate resou...

Gas hydrate (GH) is widely distributed in the world according to the geological survey. Most of GH is located in the ocean. After GH dissociation, the strength of gas hydrate bearing sediments (GHBS) decreases accompanying the rise of pore pressure, which can cause marine landslide. Landslide may transform into mudflows during movement on the seabe...

Compared with traditional fossil fuels, gas hydrates have vast reserves, cause little pollution, and are an essential strategic energy resource. Pipeline transportation is critical to realize the development and utilization of natural gas hydrate resources. The Eulerian multiphase flow model within the computational fluid dynamics software FLUENT w...

During the fracturing fluid imbibition into shale reservoirs, partial minerals could dissolve and diffuse into the fracturing fluid. However, few studies are conducted on the effects of ion diffusion on shale oil migration, especially in salt-rich shale oil reservoirs. The salt-rich shale oil reservoirs are regarded as the potential hot targets for...

Dissociation processes of gas hydrate-bearing sediment particles in water flow condition were investigated. Experiments were carried out by observing a spherical CO2 hydrate-bearing sediment (CHBS) particle settling in water. The release process of gas bubbles from CHBS particles was recorded by a high-speed camera and the total time of dissociatio...

Studying the imbibition characteristics of shale contributes to understanding the low flowback efficiency (<20%) and its potential effects on gas production. Previous studies have mainly focused on imbibition characteristics of marine shale, but few investigations have been conducted on continental shale to explore the microscopic imbibition mechan...

Gas hydrate-bearing sediments (GHBSs) have been considered as a potential energy resource. In this paper, the mechanical properties of GHBS are firstly investigated by the integrated test apparatus for synthesis of GHBS using silty sand as skeleton. Triaxial tests indicate an obvious transition of stress-strain relationship from strain hardening un...

Microscopic flow in fractured porous media is a typical problem for the exploitation of tight reservoirs. The rapid-flow in the fractured porous-media is of great significance to efficient and continuous oil/gas exploitation. The fractures are expected to enhance flow conductivity and mass transfer between matrix and fractures, and to improve oil d...

Natural gas hydrates have been treated as a potential energy resource for decades. Understanding geomechanical properties of hydrate-bearing porous media is an essential to protect the safety of individuals and devices during hydrate production. In this work, a numerical simulator named GrapeFloater is developed to study the deformation behavior of...

Gas hydrate (GH) dissociates owing to thermal injection or pressure reduction from the well in gas/oil or GH exploitation. GH dissociation leads to, for example, decreases in soil strength, engineering failures such as wellbore instabilities, and marine landslides. The FLAC3D software was used to analyze the deformation of the soil stratum and vert...

This paper presents a dual-percolation model coupling the percolation theory and the fracture percolation theory to study the conductivity of the fractured porous media. The Monte-Carlo method is used in the numerical simulation. First an appropriate computing scale by considering the calculation precision and elapsed time together is validated. Th...

A model for the elastic modulus of hydrate-bearing sediment (HBS) is presented considering the variation of the hydrate saturation and hydrate occurrence mode. The model is based on the classical series and parallel modes, introducing a parameter of statistical force transfer paths among particles in HBS. Macro-triaxial compression tests and micro...

Spatial distribution of gas hydrate dissociation is essential in analyzing gas recovery and related potential hazards. This work develops a 1D model for predicting the spatial distribution of gas hydrate dissociation under the combination of depressurization and heating in the clay-silty sediments. Without assuming a discontinuous interface and a s...

Hydrate dissociation front evolution is closely related to mining safety and gas production efficiency, is the important part of mining in-situ monitoring. Simulation experiment of methane hydrate depressurization mining was conducted for glass sand sediment samples. The influence of hydrate saturation on the seepage front and hydrate dissociation...

Methane hydrate (MH) is a new energy resource in the 21st century. But the dissociation of MH from sediments during the MH exploration or oil/gas exploration under a hydrate layer accompanied by the softening of soils and formation of excess pore gas pressure may lead to ground failures and environmental disasters. In this study, experiments on mod...

Two-phase flow model, modified Mohr-Coulomb model and the theory of unsaturated soil are adopt in FLAC, and then the characteristics of seepage flow of Beichuan soil under rainfall conditions are numerically simulated. It is shown that the initiation of rainfall-induced debris flow is affected by rainfall density and duration. The maximum horizonta...

Efficiency of Natural gas hydrate (NGH) test exploitation and spatial-temporal evolution of NGH dissociation region are analyzed through numerical analysis on the evolution of NGH dissociation region in hydrate-bearing sediments. The laws of spatial-temporal evolution and the control parameter of NGH dissociation region are obtained, and the limiti...

Taking the conglomerate from Xinjiang Oilfield as study object, the porosity distribution characteristics of the conglomerate were analyzed with CT scanning; through the online monitoring of the water and polymer flooding process in a conglomerate core using an CT scanning system, the saturation profile along the core and the CT reconstructed image...

Natural gas hydrate is an ice-like solid compound composed of mainly methane molecules and water molecules under high temperature and low temperature. Drilling and sampling in the slope of the northern South China Sea and permafrost of the Qilian Mountain have confirmed the potentially huge hydrate reserves, and the hydrate recovery is being studie...

Heat conduction and phase transformations are basic physical-chemical process and control the kinetics of dissociation, fluid flow and strata deformation during hydrate dissociation in sediments. This paper presents a simplified analysis of the thermal process by assuming that the heat-induced evolution can be decoupled from flow and deformation pr...

Seepage characteristic of hydratebearing sediments is one of the key parameters of natural gas hydrate exploitation. However, there are few literatures about experimental data of pore pressure which are closely related to seepage characteristic at present. In view of this, experiments of methane hydrate (MH) dissociation by depressurization in san...

Dynamic responses of soil foundation are difficult to analyze, though it is related to kinds of practices. In this paper, dynamic responses of soil foundation under dynamic load were analyzed theoretically. Perturbation method was used to obtain the theoretical solution. Controlling equations were about liquid-solid two-phase media. Flow, function,...

A one-dimensional model for analyzing the porous media′s deformation during and after dissociation of natural gas hydrate (NGH) was developed in which conductive-convective heat transfer,two-phase fluid flow,intrinsic kinetics of NGH dissociation and deformation of solid skeleton were all included.After the certification of the numerical model,a pa...

Multiphase fluid flow, Conductive and convective heat transfer, intrinsic kinetics of hydrate decomposition, and deformation of sediments are four basic physicalchemical processes in the exploitation of gas hydrate. The multiphase fluid flow leads to the pore pressure dissipation and the deformation of hydrate bearing sediments (HBS) accompanied b...

Rainfall is an important factor to trigger the debris flow. Numerical simulation on the responses of slopes and the initiation of debris flow under rainfall was processed by using the software FLAC2D based on the soil parameters in Weijia Gully, Beichuan County, Sichuan Province, China. The effects of the slope angle, rainfall intensity, soil param...

When water seeps upwards through a saturated soil layer, the soil layer may become instability and water films occur and develop. Water film serves as a natural sliding surface because of its very small friction. Accordingly, debris flow may happen. To investigate this phenomenon, a pseudo-three-phase media is presented first. Then discontinuity me...

A characteristic rainfall is introduced to overcome the difficulties encountered in determining a critical rainfall value for triggering debris flow. The characteristic value is defined as the rainfall at which debris-flow occurrence probability shows a rapid increase, and can be used as a warning rainfall threshold for debris flows. Investigation...

Thermally induced evolution of phase transformations is a basic physical-chemical process in the dissociation of gas hydrate in sediment (GHS). Heat transfer leads to the weakening of the bed soil and the simultaneous establishment of a time varying stress field accompanied by seepage of fluids and deformation of the soil. As a consequence, ground...

Firstly, the main factors are obtained by use of dimensionless analysis. Secondly, the time scaling factors in centrifuge modeling of bucket foundations under dynamic load are analyzed based on dimensionless analysis and controlling equation. A simplified method for dealing with the conflict of scaling factors of the inertial and the percolation in...

This paper performs experimental study on responses of the bucket foundations in calcareous sand layers under dynamic loading. Experiments to determine the horizontal static bearing capacity are carried out first. The obtained static loading-displacement curves can be referred to for determining the amplitudes of dynamic loads. Then a series of exp...

This special issue of The Open Ocean Engineering Journal features articles about dynamic responses of bucket foundations. This introductory article provides an overview and perspective for the various contributions. In recent years, suction bucket foundations have been used increasingly for gravity platform jackets, jack-ups etc. [1]. They also hav...

In this paper we investigated the responses of saturated sand under horizontal vibration loading induced by a bucket foundation. It is shown that the saturated sand liquefies gradually since the vibration loading is applied on. The maximum displacement on the surface of sand layer occurs near the loading end and in this zone the sand is compressed...

The triaxial compression test results of undisturbed, remo1ded and reconstituted samples are analyzed. The grain-size distributions and the structure are considered to be two main factors which influence the stress-strain and strength behavior of silty sands. When the grain size distributions are not the same, not only the undisturbed samples with...

In order to investigate the initiation mechanism of landslide and debris flow occurring on a gentle slope. The formation and evolution of water film (or crack) in saturated sand is analyzed by numerical and theoretical simulations under given conditions. First a psudo-three-phase model is presented considering the movement of skeleton and water and...

To study the effects of spudcan penetration on the adjacent foundations of offshore platforms, experiments and numerical simulations (using business software ABAQUS) are carried out. It is shown that the penetration of spudcan can cause the soil layer affected in an annular zone. The affected zone has a maximum width of one times the diameter of th...

Centrifugal experiments were carried out to investigate the responses of suction bucket foundations under horizontal and vertical dynamic loading. It is shown that when the loading amplitude is over a critical value, the sand at the upper part around the bucket is softened or even liquefied. The excess pore pressure decreases from the upper part to...

The experimental investigation of the response of suction bucket foundation in fine sand layer under horizontal dynamic loading has been carried out. The developments of settlement and excess pore pressure of sand foundation have been mainly studied. It is shown that the sand surrounding the bucket softens or even liquefies at the first stage if th...

The formation mechanism of “water film” (or crack) in saturated sand is analyzed theoretically and numerically. The theoretical analysis shows that there will be no stable “water film” in the saturated sand if the strength of the skeleton is zero and no positions are choked. It is shown by numerical simulation that stable water films initiate and g...

The load displacement curves of a suction bucket foundation under vertical, horizontal and combined loadings are studied experimentally. The effects of sand density on the bearing capacity are also investigated. It is shown that, under combined loading, the load conditions under which a foundation fails form a failure locus. The horizontal bearing...

In order to investigate the characteristics of water wave induced liquefaction in highly saturated sand in vertical direction, a one-dimensional model of highly saturated sand to water pressure oscillation is presented based on the two-phase continuous media theory. The development of the effective stresses and the liquefaction thickness are analyz...

Based on an assumed vertical pipeline in seabed, which contains sand and gas hydrate sediment, the deformation and stress of pipeline and sediment are numerically simulated with the different area of gas hydrate dissociation by using the business software ABAQUS. The effects of gas hydrate dissociation area and the thickness of overlaying sand sedi...