scholarly journals Numerical Modeling of Water and Gas Transport in Compacted GMZ Bentonite under Constant Volume Condition

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Jiang-Feng Liu ◽  
Xu-Lou Cao ◽  
Hong-Yang Ni ◽  
Kai Zhang ◽  
Zhi-Xiao Ma ◽  
...  
Keyword(s):  
Gas Transport ◽  
Water Saturation ◽  
Underground Water ◽  
Gas Production ◽  
Gas Pressure ◽  
Constant Volume ◽  
Gmz Bentonite ◽  
Gas Migration ◽  
Sealing Ability ◽  
High Level

During deep geological disposal of high-level and long-lived radioactive waste, underground water erosion into buffer materials, such as bentonite, and gas production around the canister are unavoidable. Therefore, understanding water and gas migration into buffer materials is important when it comes to determining the sealing ability of engineered barriers in deep geological repositories. The main aim of our study is to provide insights into the water/gas transport in a compacted bentonite sample under constant volume conditions. The results of our study indicate that water saturation is obtained after 450 hours, which is similar to experimental results. Gas migration testing shows that the degree of water saturation in the samples is very sensitive to the gas pressure. As soon as 2 MPa or higher gas pressure was applied, the water saturation degree decreased quickly. Laboratory experiments indicate that gas breakthrough occurs at 4 MPa, with water being expelled from the downstream side. This indicates that gas pressure has a significant effect on the sealing ability of Gaomizozi (GMZ) bentonite.

scholarly journals Simulation of gas transport in a landfill with layered new and old municipal solid waste

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Tao Zhang ◽  
Jianyong Shi ◽  
Xun Wu ◽  
Hai Lin ◽  
Xiulei Li
Keyword(s):  
Municipal Solid Waste ◽  
Pressure Distribution ◽  
Solid Waste ◽  
Gas Transport ◽  
Transport Model ◽  
Gas Permeability ◽  
Gas Production ◽  
Gas Pressure ◽  
Anisotropy Ratio ◽  
The Difference

AbstractAverage biodegradation rate of newly filled municipal solid waste (MSW) in landfills is relatively fast, and the landfill gas produced by the new MSW biodegradation can cause great variations in gas pressure. To predict the gas pressure distribution in the MSW layer, a one-dimensional gas transport model is established in this study. The following factors are considered in this model: (1) the variation of gas permeability with depth; (2) the anisotropy ratio of gas permeability; (3) the settlement caused by waste biodegradation. Furthermore, a single peak model for gas production is applied as the source term of gas production. The equation for settlement caused by waste biodegradation is presented, and the time of peak gas production rate is obtained by fitting the settlement of the newly filled layer. The stratification of the unsaturated and saturated regions is taken into account by distinguishing the difference in gas saturation. The layering of the new and old waste layers is considered by distinguishing the difference in the length of time that waste has been degraded to produce gas. Based on the method of numerical calculation, the gas pressure distribution in the landfill with layered new and old MSW is well simulated. The position where the maximum gas pressure occurs is found. The sensitivity analysis shows that the influence of the anisotropy ratio on gas pressure distribution is more significant.

Water and Gas Movement in Mx80 Bentonite Buffer Clay

2003 ◽  
Vol 807 ◽  
Author(s):  
Stephen T. Horseman ◽  
Jon F. Harrington ◽  
P. Sellin
Keyword(s):  
Boundary Conditions ◽  
Capillary Pressure ◽  
Gas Flow ◽  
Water Saturation ◽  
Swelling Pressure ◽  
Gas Pressure ◽  
Constant Volume ◽  
Total Stress ◽  
Porewater Pressure ◽  
Gas Pressures

ABSTRACTThis paper describes a long-term laboratory test designed to examine the sensitivity of gas flow in Mx80 buffer bentonite subject to a constant volume boundary condition. A constant volume and radial flow (CVRF) apparatus was designed to enable gas flow from a centrally located injection filter to be independently monitored at three sink-filter arrays mounted around the circumference of the clay specimen. Axial and radial total stresses and internal porewater pressure were continuously monitored. Gas entry, breakthrough and peak gas pressures were found to be systematically higher under constant volume boundary conditions than under previously reported constant stress and radially-constrained test conditions [6, 9, 10]. The observation that gas pressures are sensitive to test boundary conditions supports the hypothesis that gas entry is accompanied by dilation of the bentonite fabric. Gas penetration of the clay caused a substantial increase in total stress and internal porewater pressure. Abrupt drops in gas pressure, accompanied by similar drops in total stress, were interpreted as fracture propagation events. The outflow of gas was always non-uniformly distributed between the sinks. Furthermore, the distribution of flow between sinks often changed abruptly during the course of an experiment indicating that gas pathways were very unstable. When gas injection stopped, the gas pressure and rate of outflow spontaneously declined with time. Under constant volume conditions, the gas pressure at the asymptote exceeded the internal porewater pressure by an amount equal to the capillary pressure. In constant volume tests on clay with high water saturation, capillary pressure has a value close to the measured swelling pressure of the clay.

scholarly journals Simulation of Gas Transport in A Landfill With Layered New and Old Municipal Solid Waste

2021 ◽  
Author(s):  
Tao Zhang ◽  
Jianyong Shi ◽  
Xun Wu ◽  
Hai Lin ◽  
Xiulei Li
Keyword(s):  
Municipal Solid Waste ◽  
Pressure Distribution ◽  
Solid Waste ◽  
Gas Transport ◽  
Transport Model ◽  
Gas Permeability ◽  
Gas Production ◽  
Gas Pressure ◽  
Anisotropy Ratio ◽  
The Difference

Abstract Average biodegradation rate of newly filled municipal solid waste (MSW) in landfills is relatively fast, and the landfill gas produced by the new MSW biodegradation can cause great variations in gas pressure. To predict the gas pressure distribution in the MSW layer, a one-dimensional gas transport model is established in this study. The following factors are considered in this model: (1) the variation of gas permeability with depth; (2) the anisotropy ratio of gas permeability; (3) the settlement caused by waste biodegradation. Furthermore, a single peak model for gas production is applied as the source term of gas production. The equation for settlement caused by waste biodegradation is presented, and the time of peak gas production rate is obtained by fitting the settlement of the newly filled layer. The stratification of the unsaturated and saturated regions is taken into account by distinguishing the difference in gas saturation. The layering of the new and old waste layers is considered by distinguishing the difference in the length of time that waste has been degraded to produce gas. Based on the method of numerical calculation, the gas pressure distribution in the landfill with layered new and old MSW is well simulated. The position where the maximum gas pressure occurs is found. The sensitivity analysis shows that the influence of the anisotropy ratio on gas pressure distribution is more significant.

scholarly journals A Numerical Investigation on the Effect of Gas Pressure on the Water Saturation of Compacted Bentonite-Sand Samples

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-12
Author(s):  
Jiang-Feng Liu ◽  
Shuai-Bing Song ◽  
Jian Liu ◽  
Bing-Xiang Huang ◽  
Xu-Lou Cao ◽  
...  
Keyword(s):  
Water Saturation ◽  
Water Pressure ◽  
Gas Pressure ◽  
Sand Sample ◽  
Compacted Bentonite ◽  
Bentonite Buffer ◽  
Deep Geological Disposal ◽  
Bottom Side ◽  
High Level ◽  
Gas Pressures

In deep geological disposal for high-level radioactive waste, the generated gas can potentially affect the sealing ability of bentonite buffers. There is a competition between water and gas: the former provides sealing by swelling bentonite, and the latter attempts to desaturate the bentonite buffer. Thus, this study focused on numerically modelling the coupling effects of water and gas on the water saturation and sealing efficiency of compacted bentonite-sand samples. Different gas pressures were applied to the top surface of an upper sample, whereas the water pressure on the bottom side of the lower sample was maintained at 4 MPa. The results indicated that gas pressure did not significantly affect the saturation of the bentonite-sand sample until 2 MPa. At 2 MPa, the degree of water saturation of the upper sample was close to 1.0. As the gas pressure increased, this influence was more apparent. When the gas pressure was 6 MPa or higher, it was difficult for the upper sample to become fully saturated. Additionally, the lower sample was desaturated due to the high gas pressure. This indicated that gas pressure played an important role in the water saturation process and can affect the sealing efficiency of bentonite-based buffer materials.

scholarly journals Modelling of Pore Collapse during Polymer Sintering: Viscoelastic Model with Enclosed Gas

Materials ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2182
Author(s):  
Florian Wohlgemuth ◽  
Dirk Lellinger ◽  
Ingo Alig
Keyword(s):  
Surface Tension ◽  
Gas Transport ◽  
Selective Laser Sintering ◽  
Viscoelastic Model ◽  
Polymer Melt ◽  
Gas Diffusion ◽  
Gas Pressure ◽  
Parameter Study ◽  
Time Interval ◽  
Pore Collapse

Frenkel’s model for the late stage of coalescence of viscous particles has been extended to describe pore collapse in a viscoelastic melt during polymer sintering. The shrinkage of a pore in a polymer melt driven by surface tension is extended by taking into account the effects of trapped gas and gas transport out of the pore. Viscoelasticity has been shown to have a considerable impact on the time scale of the coalescence process. In addition, gas diffusion modifies the coalescence dynamics. Based on a parameter study, different regimes for the pore collapse have been identified. At the beginning of pore collapse, surface tension is considerably stronger than gas pressure within the pore. In this time interval (surface-tension-driven regime), the pore shrinks even in the absence of gas diffusion through the matrix. In the absence of gas transport, the shrinkage dynamic slows down and stops when the surface tension balances the gas pressure in the pore. If gas transport out of the pore is possible, surface tension and gas pressure are balanced while the gas pressure slowly decreases (diffusion-controlled regime). The final phase of pore collapse, which occurs when the gas pressure within the pore decreases sufficiently, is controlled again by surface tension. The limitations of the model are discussed. To analyze the interplay between different mechanisms and process steps during selective laser sintering, the respective time scales are compared using experimental data.

NANOSCALE PORE SIZE DISTRIBUTION EFFECTS ON GAS PRODUCTION FROM FRACTAL SHALE ROCKS

Fractals ◽  
2019 ◽  
Vol 27 (08) ◽  
pp. 1950142
Author(s):  
JINZE XU ◽  
KELIU WU ◽  
RAN LI ◽  
ZANDONG LI ◽  
JING LI ◽  
...  
Keyword(s):  
Fractal Dimension ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Gas Transport ◽  
Gas Production ◽  
Lower Sensitivity ◽  
Apparent Permeability ◽  
Transport Efficiency ◽  
Nanoscale Pore

Effect of nanoscale pore size distribution (PSD) on shale gas production is one of the challenges to be addressed by the industry. An improved approach to study multi-scale real gas transport in fractal shale rocks is proposed to bridge nanoscale PSD and gas filed production. This approach is well validated with field tests. Results indicate the gas production is underestimated without considering a nanoscale PSD. A PSD with a larger fractal dimension in pore size and variance yields a higher fraction of large pores; this leads to a better gas transport capacity; this is owing to a higher free gas transport ratio. A PSD with a smaller fractal dimension yields a lower cumulative gas production; this is because a smaller fractal dimension results in the reduction of gas transport efficiency. With an increase in the fractal dimension in pore size and variance, an apparent permeability-shifting effect is less obvious, and the sensitivity of this effect to a nanoscale PSD is also impaired. Higher fractal dimensions and variances result in higher cumulative gas production and a lower sensitivity of gas production to a nanoscale PSD, which is due to a better gas transport efficiency. The shale apparent permeability-shifting effect to nanoscale is more sensitive to a nanoscale PSD under a higher initial reservoir pressure, which makes gas production more sensitive to a nanoscale PSD. The findings of this study can help to better understand the influence of a nanoscale PSD on gas flow capacity and gas production.

The Method of Dynamic Reserves Prediction for a Constant Volume Gas Reservoir

2013 ◽  
Vol 275-277 ◽  
pp. 456-461
Author(s):  
Lei Zhang ◽  
Lai Bing Zhang ◽  
Bin Quan Jiang ◽  
Huan Liu
Keyword(s):  
Pressure Drop ◽  
Material Balance ◽  
Production Method ◽  
Gas Production ◽  
Constant Volume ◽  
Phase Method ◽  
Gas Reservoirs ◽  
Two Phase ◽  
Material Balance Method ◽  
Unit Pressure

The accurate prediction of the dynamic reserves of gas reservoirs is the important research content of the development of dynamic analysis of gas reservoirs. It is of great significance to the stable and safe production and the formulation of scientific and rational development programs of gas reservoirs. The production methods of dynamic reserves of gas reservoirs mainly include material balance method, unit pressure drop of gas production method and elastic two-phase method. To clarify the characteristics of these methods better, in this paper, we took two typeⅠwells of a constant volume gas reservoir as an example, the dynamic reserves of single well controlled were respectively calculated, and the results show that the order of the calculated volume of the dynamic reserves by using different methods is material balance method> unit pressure drop of gas production method >elastic two-phase method. Because the material balance method is a static method, unit pressure drop of gas production method and elastic two-phase method are dynamic methods, therefore, for typeⅠwells of constant volume gas reservoirs, when the gas wells reached the quasi-steady state, the elastic two-phase method is used to calculate the dynamic reserves, and when the gas wells didn’t reach the quasi-steady state, unit pressure drop of gas production method is used to calculate the dynamic reserves. The conclusion has some certain theoretical value for the prediction of dynamic reserves for constant volume gas reservoirs.

Analysis of Premium Connection of Connecting and Sealing Ability Loaded by Axial Tensile Loads

2012 ◽  
Vol 268-270 ◽  
pp. 737-740
Author(s):  
Yang Yu ◽  
Yi Hua Dou ◽  
Fu Xiang Zhang ◽  
Xiang Tong Yang
Keyword(s):  
Finite Element ◽  
Contact Pressure ◽  
Tensile Load ◽  
Element Model ◽  
Sealing Ability ◽  
Axial Tensile ◽  
High Level ◽  
Maximum Contact ◽  
Contact Pressures ◽  
The Finite Element Model

It is necessary to know the connecting and sealing ability of premium connection for appropriate choices of different working conditions. By finite element method, the finite element model of premium connection is established and the stresses of seal section, shoulder zone and thread surface of tubing by axial tensile loads are analyzed. The results show that shoulder zone is subject to most axial stresses at made-up state, which will make distribution of stresses on thread reasonable. With the increase of axial tensile loads, stresses of thread on both ends increase and on seal section and shoulder zone slightly change. The maximum stress on some thread exceed the yield limit of material when axial tensile loads exceed 400KN. Limited axial tensile loads sharply influence the contact pressures on shoulder zone while slightly on seal section. Although the maximum contact pressure on shoulder zone drop to 0 when the axial tensile load is 600KN, the maximum contact pressure on seal section will keep on a high level.

Lateral gas transport in soil adjacent to an old landfill: factors governing gas migration

2001 ◽  
Vol 19 (2) ◽  
pp. 144-159 ◽  
Author(s):  
Mette Christophersen ◽  
Peter Kjeldsen
Keyword(s):  
Gas Transport ◽  
Gas Migration
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