Insights into gas migration behavior in saturated GMZ bentonite under flexible constraint conditions

2021 ◽  
Vol 287 ◽  
pp. 123070
Author(s):  
Lin-yong Cui ◽  
Wei-Min Ye ◽  
Qiong Wang ◽  
Yong-Gui Chen ◽  
Bao Chen ◽  
...  
Keyword(s):  
Gmz Bentonite ◽  
Migration Behavior ◽  
Gas Migration

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.

A Study on Gas Migration Behavior in Buffer Material using X-ray CT Method

2006 ◽  
Vol 932 ◽  
Author(s):  
K. Tanai ◽  
M. Yui
Keyword(s):  
Water Saturation ◽  
Gas Injection ◽  
Swelling Pressure ◽  
Digital Data ◽  
Migration Behavior ◽  
Gas Migration ◽  
Migration Test ◽  
X Ray ◽  
Compacted Bentonite ◽  
Buffer Material

ABSTRACTThis paper presents a study on gas migration behavior in a bentonite specimen with the aid of X-ray computer tomography (CT) scan data. The laboratory experiment was carried out to clarify gas migration behavior through saturated, compacted bentonite. X-ray CT was used to estimate the spatial distribution of gas and water saturation during gas migration test in the bentonite. For the gas migration test, the controlled flow rate of gas injection was adopted for pre-compacted samples of Kunigel V1 bentonite using helium gas, which is safer than hydrogen gas.A specimen was isotropically consolidated and saturated by synthetic seawater, simultaneously, by applying a backpressure. This was followed by injecting the gas using a syringe pump. Inlet and outlet gas fluxes were monitored. This test exhibited a significant threshold pressure for breakthrough, somewhat larger than the sum of the swelling pressure and the backpressure.The procedure of the X-ray CT measurement is as follows; i) measurement of the initial condition (saturated condition) of the compacted bentonite, ii) measurement of the gas injection condition as a function of time. The digital data obtained from the X-ray CT usually includes some noise. The stacking method can reduce the noise in CT values and enables to identify the gas migration area. The results indicate that gas is transported through preferential pathways in compacted bentonite, and is not homogenous.

scholarly journals Study of methane migration in the shallow subsurface from a gas pipe leak

Elem Sci Anth ◽  
2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Bo Gao ◽  
Melissa K. Mitton ◽  
Clay Bell ◽  
Daniel Zimmerle ◽  
T. K. K. Chamindu Deepagoda ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Natural Gas ◽  
Dominant Role ◽  
Meteorological Data ◽  
Leak Rate ◽  
Soil Conditions ◽  
Migration Behavior ◽  
Gas Migration ◽  
Methane Distribution ◽  
Methane Concentrations

With the increased use of natural gas, safety and environmental concerns from underground leaking natural gas pipelines are becoming more widespread. What is not well understood in leakage incidents is how the soil conditions affect gas migration behavior, making it difficult to estimate the gas distribution. To shed light on these concerns, an increased understanding of subsurface methane migration after gas release is required to support efficient leak response and effective use of available technologies. In this study, three field-scale experiments were performed at the Methane Emission Technology Evaluation Center in Colorado State University to investigate the effect of soil textural heterogeneity, soil moisture, and leak rate (0.5 and 0.85 kg/h) on methane migration caused by leaking pipelines. Subsurface methane concentrations, in addition to soil moisture and meteorological data, were collected over time. A previously validated numerical model was modified and used to understand the observed methane distribution behavior. Results of this study illustrate that the influence of soil texture, leak rate, and moisture on subsurface methane distribution is determined by the relative contribution of advection and diffusion and closely related to the distance to the leak source. Advection dominates gas transport within 1–1.5 m of the leak source, driving the migration of high concentration contours. Beyond this distance, diffusion dominates migration of lower concentration contours to the far-field. Although large leak rates initially result in faster and further gas migration, the leak rate has little influence on the diffusion dominated migration farther from the leak source. Soil moisture and texture complicate gas behavior with texture variations and elevated soil moisture conditions playing a dominant role in locally increasing methane concentrations. Scenarios highlight the importance of understanding the effects of soil moisture, texture, and leak rate on gas migration behavior in an attempt to unravel their contribution to the gas concentration within the soil environment.

Gas breakthrough in saturated compacted GaoMiaoZi (GMZ) bentonite under rigid boundary conditions

2017 ◽  
Vol 54 (8) ◽  
pp. 1139-1149 ◽  
Author(s):  
L. Xu ◽  
W.M. Ye ◽  
B. Ye
Keyword(s):  
Water Retention ◽  
Swelling Pressure ◽  
Dry Density ◽  
Gmz Bentonite ◽  
Gas Migration ◽  
Migration Process ◽  
Rigid Boundary ◽  
Capillary Effects ◽  
Entry Pressure ◽  
Breakthrough Pressure

In a geological repository for disposal of high-level radioactive waste, gas breakthrough is an important phenomenon during a gas migration process in the saturated engineered barrier. In this paper, gas injection, swelling pressure, water permeability, and water retention tests were conducted on saturated compacted GaoMiaoZi (GMZ) bentonite to investigate the gas breakthrough mechanism. Results show that, for saturated GMZ bentonite tested under rigid boundary conditions, the gas breakthrough pressure is significantly larger than the swelling pressure and slightly lower than the gas entry pressure obtained from the water retention characteristic and the van Genuchten model. Gas breakthrough pressure deviates from the swelling pressure and approaches the calculated gas entry pressure as the dry density increases. Mechanical and capillary effects are both important to the gas migration process for specimens with lower dry densities, and the capillary effect becomes more important with the increase of dry density. The desaturation and shrinkage of the specimen will result in unexpectedly high and disordered interfacial gas flux. For specimens with higher dry densities, gas will only flow through interconnected larger pores, then result in minor desaturation–shrinkage of the specimen. Finally, a new model with consideration of both mechanical and capillary effects is proposed, which can accurately predict gas breakthrough pressure for a GMZ bentonite specimen.

Development of Numerical Simulation Method for Gas Migration Through Highly-Compacted Bentonite Using Model of Two-Phase Flow Through Deformable Porous Media

2010 ◽  
Author(s):  
Yukihisa Tanaka
Keyword(s):  
Porous Media ◽  
Two Phase Flow ◽  
Migration Behavior ◽  
Phase Flow ◽  
Gas Migration ◽  
Two Phase ◽  
Deformable Porous Media ◽  
Compacted Bentonite ◽  
Flow Through ◽  
Engineered Barrier

In the current concept of repository for radioactive waste disposal, compacted bentonite will be used as an engineered barrier mainly for inhibiting migration of radioactive nuclides. Hydrogen gas can be generated inside of the engineered barrier by anaerobic corrosion of metals used for containers, etc. It is expected to be not easy for gas to entering into the bentonite as a discrete gaseous phase because the pore of compacted bentonite is so minute. Therefore it is necessary to investigate the effect of gas pressure generation and gas migration on the engineered barrier, peripheral facilities and ground. In this study, a method for simulating gas migration through the compacted bentonite is proposed. The proposed method can analyze coupled hydrological-mechanical processes using the model of two-phase flow through deformable porous media. Validity of the proposed analytical method is examined by comparing gas migration test results with the calculated results, which revealed that the proposed method can simulate gas migration behavior through compacted bentonite with accuracy.

scholarly journals Effect of Surface Type on the Flow Characteristics in Shale Nanopores

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Shiyuan Zhan ◽  
Yuliang Su ◽  
Mingjing Lu ◽  
Mingyu Cai ◽  
Jingang Fu ◽  
...  
Keyword(s):  
Pore Size ◽  
Shale Gas ◽  
Adsorption Layer ◽  
Flow Behavior ◽  
Knudsen Layer ◽  
Flow Mode ◽  
Migration Behavior ◽  
Gas Migration ◽  
Surface Type ◽  
Gas Flux

The underlying mechanism of shale gas migration behavior is of great importance to understanding the flow behavior and the prediction of shale gas flux. The slippage of the methane molecules on the surface is generally emphasized in nanopores in most predicted methods currently. In this work, we use molecular dynamic (MD) simulations to study the methane flow behavior in organic (graphene) and inorganic (quartz) nanopores with various pore size. It is observed that the slippage is obvious only on the graphene nanopores and disappeared on the quartz surface. Compared with the traditional Navier-Stokes equation combined with the no-slip boundary, the enhancement of the gas flux is nonnegligible in the graphene nanopores and could be neglected in the quartz nanopores. In addition, the flux contribution ratios of the adsorption layer, Knudsen layer, and the bulk gas are analyzed. In quartz nanopores, the contributions of the adsorption layer and the Knudsen layer are slight when the pore size is larger than 10 nm. It is also noted that even if the Knudsen number is the same, the flow mode may be various with the effect of the pore surface type. Our work should give molecular insights into gas migration mechanisms in organic and inorganic nanopores and provide important reference to the prediction of the gas flow in various types of shale nanopores.

scholarly journals Geological CO2 quantified by high-temporal resolution stable isotope monitoring in a salt mine

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Alexander H. Frank ◽  
Robert van Geldern ◽  
Anssi Myrttinen ◽  
Martin Zimmer ◽  
Johannes A. C. Barth ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Underground Mining ◽  
Stable Carbon Isotope ◽  
Underground Mines ◽  
Background Concentration ◽  
High Temporal Resolution ◽  
Salt Mine ◽  
Gas Migration ◽  
Mining Operations ◽  
Anthropogenic Contributions

AbstractThe relevance of CO2 emissions from geological sources to the atmospheric carbon budget is becoming increasingly recognized. Although geogenic gas migration along faults and in volcanic zones is generally well studied, short-term dynamics of diffusive geogenic CO2 emissions are mostly unknown. While geogenic CO2 is considered a challenging threat for underground mining operations, mines provide an extraordinary opportunity to observe geogenic degassing and dynamics close to its source. Stable carbon isotope monitoring of CO2 allows partitioning geogenic from anthropogenic contributions. High temporal-resolution enables the recognition of temporal and interdependent dynamics, easily missed by discrete sampling. Here, data is presented from an active underground salt mine in central Germany, collected on-site utilizing a field-deployed laser isotope spectrometer. Throughout the 34-day measurement period, total CO2 concentrations varied between 805 ppmV (5th percentile) and 1370 ppmV (95th percentile). With a 400-ppm atmospheric background concentration, an isotope mixing model allows the separation of geogenic (16–27%) from highly dynamic anthropogenic combustion-related contributions (21–54%). The geogenic fraction is inversely correlated to established CO2 concentrations that were driven by anthropogenic CO2 emissions within the mine. The described approach is applicable to other environments, including different types of underground mines, natural caves, and soils.

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