Showing papers by "Xiao-Sen Li published in 2018"

Tri-Axial Shear Tests on Hydrate-Bearing Sediments during Hydrate Dissociation with Depressurization

Abstract: A series of tri-axial shear tests were carried out to determine the stress and strain characteristics, as well as the volume deformation of methane hydrate-bearing sediments during gas hydrate dissociation. An innovative type of depressurization was adopted with a high-pressure and low-temperature tri-axial apparatus. Results show that: (1) decrease in pore pressure during the shear process may result in the failure of hydrate-bearing sediments, but they did not collapse completely due to high effective confining pressure; (2) depressurization leads to the contraction of volumetric strain and the ultimate deformation shows no difference compared to that prior depressurization; (3) high saturation hydrate-bearing sediments were more sensitive to depressurization, which could be due to the methane hydrate acting as a skeleton structure at some sites when the pore hydrates’ saturation is high.

The Formation of CH4 Hydrate in the Slit Nanopore between the Smectite Basal Surfaces by Molecular Dynamics Simulation

Abstract: Natural gas hydrate (NGH) formation behavior in porous sediment influences the investigation of the reservoirs and the exploitation of NGH. However, its molecular mechanisms of NGH formation in the porous sediment remain unclear. In this work, we present the CH4 hydrate formation in the smectite system through molecular dynamics simulation. The microstructure molecular configurations and properties are analyzed. The results find the pure H2O solution and the CH4-H2O homogeneous solution in the initial configuration of the smectite layer reveal the different influence on the hydrate formation. The gas–water ratio (ri) affects the molecular diffusion and the hydrate formation. In the smectite layer, the two types of arrangements of cages are present: the semi-cage arrangement and the link-cage arrangement. The silicon-oxygen ring of the smectite surface connecting with the two types of arrangements of cages has the stable effect for the hydrate formation in the smectite.

Recovery of methane from coal-bed methane gas mixture via hydrate-based methane separation method by adding anionic surfactants

Abstract: To screen a preferable kinetics promoter, the effects of sodium dodecyl sulfate (SDS) and sodium dodecyl benzene sulfonate (SDBS) within tetrahydrofuran (THF) solution on recovering methane (CH4) f...

Hydrate-Based CO2 Capture from Integrated Gasification Combined Cycle Syngas with Tetra-n-butylammonium Bromide and Nano-Al2O3

Abstract: Hydrate-based CO2 capture and/or H2 purification from integrated gasification combined cycle (IGCC) syngas has been a more and more attractive technology in both environmental and clean energy fields. This work focused on both microcosmic and macroscopic studies for the CO2/H2 hydrate formation process with synergic additives comprised of tetra-n-butylammonium bromide (TBAB) and nano-Al2O3. The experiments were carried out with 0.5 wt % nano-Al2O3 and 1, 5, 10, and 11 wt % TBAB. The microcosmic study shows that, with the synergic additives, the CO2/H2 mixture hydrate formed mainly on the nano-Al2O3 surface and formed a semiclathrate structure. Additionally, the macroscopic study shows that the synergic additives could remarkably promote the gas uptake and separation efficiency. Noteworthy, in comparison to unitary TBAB, tetrahydrofuran, and cyclopentane, the synergic additives could increase the gas uptake for the CO2/H2 hydrate formation process by approximately 43.62, 230.56, and 173.27%, respectively. ...

Experimental study on hydrate anti-agglomeration in the presence of rhamnolipid

Abstract: Gas hydrates might cause a potential safety hazard in subsea flow assurance. Anti-agglomeration is a promising approach to keep subsea oil and gas pipelines free from hydrate risks. Effective anti-agglomerants could prevent hydrate agglomeration of small crystallites by lowering the capillary force between hydrate particles. Biosurfactants are widely known for their eco-friendly nature. In this work, n-octane, water and methane were used as hydrate-forming ingredients to examine the effectiveness of rhamnolipid. Our investigation was carried out at constant high pressure (10 MPa) with different water cuts, subcooling degrees and rhamnolipid mass fractions. Three agglomeration states of hydrate were observed in a high-pressure visual autoclave apparatus. Torque measurements showed that rhamnolipid could effectively prevent hydrate agglomeration with a concentration of 0.5 wt%. In addition, the structural characteristics and morphology of hydrate were observed by use of powder X-ray diffraction, Raman spectroscopy and cryo-scanning electron microscopy. We noticed that the introduction of rhamnolipid had no effect on hydrate structure, but it could increase the large and small cavity ratio value and hydration number. Through the microscopic images, we inferred that rhamnolipid could make the surface of hydrate smooth, which resulted in a more ordered surface.

Anti-Agglomerator of Tetra-n-Butyl Ammonium Bromide Hydrate and Its Effect on Hydrate-Based CO2 Capture

Abstract: Tetra-n-butyl ammonium bromide (TBAB) was widely used in the research fields of cold storage and CO2 hydrate separation due to its high phase change latent heat and thermodynamic promotion for hydrate formation Agglomeration always occurred in the process of TBAB hydrate generation, which led to the blockage in the pipeline and the separation apparatus In this work, we screened out a kind of anti-agglomerant that can effectively solve the problem of TBAB hydrate agglomeration The anti-agglomerant (AA) is composed of 90% cocamidopropyl dimethylamine and 10% glycerol, which can keep TBAB hydrate of 193–290 wt % in a stable state of slurry over 72 h The microscopic observation of the morphology of the TBAB hydrate particles showed that the addition of AA can greatly reduce the size of the TBAB hydrate particles CO2 gas separation experiments found that the addition of AA led to great improvement on gas storage capacity, CO2 split fraction and separation factor, due to the increasing of contact area between gas phase and hydrate particles The CO2 split fraction and separation factor with AA addition reached up to 703% and 428%, respectively

Gas-Lifting Characteristics of Methane-Water Mixture and Its Potential Application for Self-Eruption Production of Marine Natural Gas Hydrates

Abstract: A gas-lifting production method was firstly proposed to transport the methane-water mixture from natural gas hydrates deposits through marine vertical pipe in this work. Aiming at UBGH2-6 site, SH7 site and GMGS2-8 site, the gas-lifting performance of methane-water mixture in the vertical pipe was investigated by numerical calculation. The potential of Natural gas hydrates (NGH) self-eruption production induced by the gas-lifting process under ideal conditions was also studied based on the energy analysis. The calculation results indicate that the gas-lifting method has great advantage in avoiding the secondary hydrates formation in marine vertical pipe and reducing energy consumption. The gas-lifting process in the vertical pipe is testified to be spontaneous in UBGH2-6 site and SH7 site during the initial 4000 and 1000 days, respectively, which indicates the energy consumption for methane-water mixture transportation is saved. Sufficient heat supply for the hydrate dissociation is crucial for the NGH self-eruption production. Sensitivity analysis indicates that the water-gas ratio has more significant influences on gas-lifting performance in the vertical pipe compared to the flow rate. With the decrease of water-gas ratio, the bottomhole pressure decreases rapidly. Thus, the reduction of water production is effective to improve the gas-lifting performance.

Study on Temperature Characteristics of Hydrate Slurry during Cyclopentane–Methane Hydrate Formation

Abstract: In this work, the temperature characteristics of hydrate slurry related to transition heat in the cyclopentane (CP)/methane (CH4) hydrate formation process were systematically investigated. A cryst...

Gas-exploitation method and system for natural gas hydrate exploitation

Abstract: The invention discloses a gas-exploitation method and system for natural gas hydrate exploitation. Natural gas hydrates are utilized to decompose the gas lift effect of released methane gas, a gas-water mixture at the well bottom of an exploitation well is conveyed to a sea surface platform through an ocean riser, and thus controllable flowing exploitation of the ocean natural gas hydrates is achieved; at the exploitation starting stage, through the gas stripping effect of externally-injected gas, the well bottom pressure is reduced, and thus the hydrates are decomposed; and at the flowing exploitation stage, flowing exploitation is achieved through the gas lift effect of the natural gas hydrate decomposing gas, through a seabed gas storage tank, the flowing speed is adjusted, and gas consumption is supplemented. The gas exploitation technique and equipment are simple, operation is convenient, energy consumption is low, seabed movable equipment is not needed, industrial and automatic production is easy to achieve, the blockage risk caused by forming of secondary hydrates in the ocean riser can be avoided effectively, and the application range is wide.

Experimental device and method used for polyphase separation of natural gas hydrate drilling fluid

Abstract: An experimental device of polyphase separation of natural gas hydrate drilling fluid, and method of use thereof, comprising a solid-phase separator, a liquid injection module, a gas injection module and a gas-liquid separator. The solid-phase separator comprises a first filter device and a second filter device, the gas injection module injects gas into the solid-phase separator while the liquid injection module injects liquid into the solid-phase separator, and the gas-liquid separator is communicated with the solid-phase separator through a pressure control valve. In the experimental device and method, the combination of the liquid and the gas injection modules keeps the solid-phase separator in a high-pressure state of the gas-liquid mixture constantly to achieve the polyphase separation of natural gas hydrate drilling fluid under a high pressure, while avoiding the formation of new hydrates during separation; the provision of the dual-filter device in the solid-phase separator aids in preventing equipment blockages.

Device and method for separating co2 gas by hydrate method combined with chemical absorption method

Abstract: Disclosed are a device and method for separating CO2 gas by a hydrate method combined with a chemical absorption method. The combination of the hydrate method and the chemical absorption method can realize a high-efficiency and continuous separation of CO2 gas without the need of recompression, thereby greatly reducing operation costs, and advantageously alleviating the production of secondary pollution; and can not only apply to the CO2 separation in an IGCC synthesis gas, but also can apply to the CO2 separation in a natural gas and a biogas, solving the problems of a high energy consumption, a low handling amount and secondary pollution encountered in current CO2 separation and hydrogen purification technologies for the IGCC synthesis gas.

Gas-liquid separation apparatus suitable for gas hydrate slurry

Abstract: A gas-liquid separation apparatus suitable for gas hydrate slurry, comprising an upper chamber, a middle chamber, and a lower chamber; a gas-phase outlet and a pressurizing unit are disposed in a top of the upper chamber, the middle chamber is provided with a material inlet and a wire mesh demister, and the lower chamber is provided with a liquid-phase outlet and a plurality of deflector baffles. The arrangement of divided chambers can reduce the degree of hydrate dissociation in the slurry (i.e., loss of the sought gas) and improve the separation efficiency. With the pressurizing unit, it facilitates the setting of the required pressure for gas-liquid separation without introducing a pressure maintaining valve in the subsequent separation process, prevents the hydrate in the slurry from dissociating in the apparatus, and allows rapid separation between the slurry and the gas.

Apparatus and combined process for carbon dioxide gas separation

Abstract: An apparatus and a combined process for carbon dioxide gas separation, combining the hydrate-based process with the chemical absorption process, which reduces secondary pollution and allows the efficient continuous separation of carbon dioxide gas without increasing the pressure and thereby the operating cost is reduced significantly. The apparatus and combined process can be applied in the separation of carbon dioxide in IGCC synthetic gas, natural gas and biogas, and address the issues of the existing processes such as high energy consumption, low throughput, and secondary pollution.

Experimental device and method for studying relationship between sediment yield behavior and radial deformation of porous media during exploitation of natural gas hydrates

Abstract: Disclosed is an experimental device for studying the sediment yield behavior and the radial deformation of porous media during the exploitation of natural gas hydrates, comprising a high-pressure reactor, a hydrate sample chamber, a simulated wellbore, a deformation measurement unit, an ambient temperature control unit, an outlet control unit, an inlet control unit and a data processing unit. Further disclosed is a method using the above-mentioned experimental device to carry out experiments. The experimental device and method according to the present invention can conveniently measure the deformation of the porous media during the decomposition of the hydrates and simulate the sediment producing situation in the wellbore, can simulate the sediment yield problem during the exploitation of natural gas hydrates as well as the gas-liquid-solid flowing problem in the wellbore during the exploitation of natural gas hydrates, and can accurately obtain the gas-solid-liquid three-phase yields in real time during the decomposition of natural gas hydrates. Being simple to operate and easy to control, and suitable for various sizes and shapes of reactors, it can provide basic experimental data and a theoretical basis for the technologies of hydrate exploitation.