Characteristics Of Gas Migration Research Articles

Gas migration characteristics in vehicle tank under different ventilation conditions

In recent years, due to the frequent occurrence of accidents in confined space operations, horizontal ammonia tank trucks with higher accident frequencies were selected for numerical simulation research through comparative analysis. The ammonia concentration variation characteristics of horizontal ammonia tank cars were simulated under four conditions: natural ventilation with 0° incoming air, natural ventilation with 45° incoming air, mechanical ventilation with extraction, and mechanical ventilation with compression. The results indicate that natural ventilation requires 48 h to reduce the ammonia concentration to a safe range for operation, while mechanical ventilation reduces the ammonia concentration to infinity and approaches zero within 30 min according to regulations, making the working environment safer; Set up monitoring points inside the tank to monitor the gas disturbance inside the tank at different wind speeds. Based on the ammonia concentration cloud map and the monitoring point wind speed, it can be concluded that local ammonia accumulation is more likely to occur on both sides of the tank due to poor ventilation. Comparing and analyzing the simulated values with theoretical calculations and experiments, it was found that there are differences in the degree of gas change but the overall trend is the same. This indicates that ventilation simulation and the determination of ammonia migration characteristics have practical significance for guiding on-site operations.

Study on prediction of sustained casing pressure in tubing-casing annulus based on bubble migration experiment

Sustained casing pressure (SCP) due to tubing leakage is an unwanted condition for well barrier reliability and gas well management and can affect well integrity. Therefore, studying the SCP prediction in the tubing-casing annulus to reduce the potential risk in the wellbore is critical. Almost all available research neglects the effect of the migration of the gas in the annulus on the SCP. In this research, a prediction model of the SCP is developed by integrating the gas migration. Meanwhile, a device is being experimentally developed according to the similarity principle. Based on the simulation experiments, the gas migration characteristics are investigated, and the accuracy of the prediction model of the gas migration is verified. Then, a numerical model is established for the SCP to further evaluate the validity of the SCP prediction model and the effect of the gas migration on the SCP. Finally, a case study is conducted on a high-pressure gas well of the SCP to investigate the effects of the condition parameters of the well on the SCP and the gas migration. The obtained results indicate that the position of the tubing leakage and the liquid density in the annulus has an impact on the balance value and recovery rate of the SCP. The gas migration has no effect on the balance value of the SCP, but it does alter the initial recovery rate of the SCP. The work presented provides a reliable prediction method for the accurate description of the SCP process.

Experimental Study on the Effect of CO2 Injection Pressure on the Migration Characteristics and Extraction Effects of Replacement CH4.

To study the effect of CO2 injection pressure on gas migration characteristics and coalbed methane (CBM) extraction, a platform for the experimental replacement of CH4 with CO2 was used to conduct experiments on the replacement of CH4 under different CO2 injection pressures and analyze the gas transport characteristics and CH4 extraction during the experiment. The results reveal that the rate of gas migration out of the coal seam accelerates with increasing gas injection pressure, as determined by comparisons of the migration rates between adjacent monitoring points. The change trend of the CH4 desorption rate under different gas injection pressures is divided into slow decline, sharp decline, and stability stages, and the maximum value of the effective diffusion coefficient increases from 2.3 × 10-5 to 3.4 × 10-5 and 4.6 × 10-5 cm2/s as the gas injection pressure increases from 0.6 to 0.8 and 1.0 MPa. Similarly, the change pattern of coal seam permeability can be divided into slow decline, sharp decline, and stability stages. After the gas injection pressure was increased from 0.6 to 0.8 and 1.0 MPa, the CH4 desorption volume increased from 90.2 to 94.1 and 97.8 L, whereas the coal seam CO2 sequestration volume increased from 269.2 to 274.2 and 322.8 L, respectively. In contrast, the CH4 extraction efficiency increased from 76.9 to 80.2 and 82.9%, respectively. The research results have important reference value and practical significance for optimizing the CO2 injection pressure and improving the CBM extraction.

Analysis of fault orientation and gas migration characteristics in front of coal mining face: Implications for coal-gas outbursts

Coal in a natural geological mass is typically heterogeneous, potentially containing widely distributed faults that affect gas migration and are closely associated with the occurrence of coal-gas outbursts. In this study, the permeabilities of intact and heterogeneous coals during the mining process were described using a dual-porosity model and modified transversely isotropic permeability model, respectively. Numerical simulations based on these models revealed a high gas pressure gradient in front of the working face largely owing to the blocking effect of a low-permeability zone along the fault that led to the formation of a high-pressure gas zone; field measurements confirmed that the gas content in this zone was 2–3 times that in ordinary coal. When close to the fault, a considerable quantity of gas was observed within the working face, then the gas emission increased by 2.4 times once the low-permeability zone along the fault was obliterated. Finally, the proposed model was employed to explain how concurrent increases in shear stress and gas pressure affect the stability of a fault and promote coal-gas outbursts. The proposed model can be applied to conduct theoretical assessments informing measures to prevent gas-related dynamic disasters in coal mines.

Representation of mining permeability and borehole layout optimization for efficient methane drainage

The development of a cost-effective and accurate permeability characterization method for large-scale mining overburden conditions is topical for engineering assessment of mine water and gas migration characteristics. Based on laboratory test results, a new permeability characterization method considering loading–unloading times and elastic–plastic stress evolution is proposed, which is realized by fish language embedded in FLAC 3D software. The proposed method is first compared with other available models via the inversed experimental results and then applied to evaluate the protected seam permeability-enhanced range. The COMSOL Multiphysics and FLAC data interaction is used to optimize the protected seam extraction borehole layout. It is shown that the proposed model can characterize the permeability evolution more accurately than other (elastic, damage strain) models. The protected seam stress paths have non-equal loading and unloading amplitudes in vertical and horizontal directions, while its permeability is divided into six areas and the enhanced area exceeds that of the gob. Based on the permeability zoning characteristics, the non-uniform layout parameters of extraction boreholes are quantified to achieve the identical-size layout of working faces of the protected and protective seams and reduced workload of extraction boreholes.

Influences of path control effects on characteristics of gas migration in a coal reservoir

In this paper, the influences of path control effects on characteristics of gas migration in coal samples with different sizes were investigated by using self-developed test device. Moreover, the mathematical model regarding path control effects on the gas migration was established. The results show that the curves of gas diffusion velocity in the coal samples with different sizes gradually decrease and then flatten with diffusion time. At the initial stage of diffusion, the gas diffusion velocity in coal samples with a small geometric size (short migration path) is larger than that in the coal samples with a large geometric size (long migration path). However, with the test proceeding, the phenomenon of velocity transcendence appears. The cumulative gas diffusion from the coal samples increases sharply with the rise of gas diffusion velocity, and its growth rate decreases gradually with the decrease of gas diffusion velocity. Finally, the gas diffusion curve tends to be flat. Although there is a phenomenon of transcendence in the gas diffusion velocity, transcendence in the cumulative gas diffusion has not been found. By equating the free space around the coal samples into a large fracture connecting to the coal samples, a fracture system was formed together with pore structures in the coal samples to affect gas migration process.

Gas extraction challenge and the application of hydraulic cavity technology in the Shijiazhuang coalmine, Qinshui basin

ABSTRACT Hydraulic cavity has been demonstrated to be an efficient gas extraction technology in the single, soft, and low-permeability coal seam in China. However, the permeability evolution around hydraulic cavity has not been fully understood due to the lack of the permeability model in the post-peak stage, which leads to a great challenge for the gas extraction simulation and thus the borehole design. Therefore, we developed a fully coupled dual-porosity gas extraction model that considers the effects of coal damage on the permeability evolution. Based on this model, we analyzed the permeability evolution and the gas migration characteristics around the hydraulic cavity and designed a hydraulic cavity scheme for the Shijiazhuang coalmine. The field application results prove that our simulation results are correct.

Evaluation of Gas Migration and Rock Damage Characteristics for Underground Nuclear Waste Storage Based on a Coupled Model

In the deep geological repository of nuclear waste, the corrosion of waste generates gas, which increases the storage pressure, changes the properties of the rock strata, and affects the stability of nuclear waste repository. Therefore, it is of great importance to understand the gas migration in the engineering barrier and the potential impact on its integrity for the safety assessment of nuclear waste repository. A hydro-mechanical-damage model for analyzing gas migration in sedimentary rocks is established in this paper. On the basis of which, a set of coupled formulas for the coupling of gas migration in rock mass is established. The model considers the characteristics of gas migration in sedimentary rock, especially the microcracks caused by the degradation of elastic modulus and damage, and the coupling between the rock deformation and failure of fractures. The numerical simulation of gas injection test is beneficial to understand the mechanism of gas migration process in sedimentary rock.

Characterization methods for mass transfer of multiple media in shale gas reservoirs

Shale gas reservoirs are abound in multi-scale pore media and have strong heterogeneity. Gas migration mechanism in different scale pores is complex. Understanding the applicability of mass transfer characterization method for multi-media fluid is of great significance to develop numerical simulation of shale gas reservoirs. On the basis of multi-scale media distribution characteristics and the gas migration characteristics in multi-scale media of shale gas reservoirs, this paper establish the discrete media REV model, transient-cross-flow dual-media REV model, and pseudo-state-cross-flow dual-media REV model for microcells in different regions of reservoirs. The flow behavior of the microcells calculated by the above three models is compared with reservoir conditions and fracture parameters. The suitable rang of different mass transfer characterization methods for multiple media is proposed. The results showed that the cross-flow mode have a great effect on mass transfer on the early period. The greater the difference of dual media, the bigger the difference of mass transfer calculated by different cross-flow mode, the longer the duration of the difference of mass transfer. The transient-cross-flow dual-media model, and pseudo-state-cross-flow dual-media model can both accurately describe the mass transfer between porous kerogen and inorganic matrix. Mass transfer between inorganic matrix and secondary fractures should be described by discrete media model. The discrete fracture network coupled porous kerogen-inorganic matrix dual medium model can be more accurately for description of gas migration in shale gas reservoirs with stimulated reservoir volume. The model has important theoretical significance for developing numerical simulator for shale gas reservoirs.

Laboratory gas injection tests of compacted bentonite buffer material for TRU waste disposal

AbstractThe Radioactive Waste Management Funding and Research Center (RWMC) is leading a research programme to evaluate the gas transport mechanisms through a TRU (TRans-Uranium) waste disposal facility in Japan and acquire information on gas migration properties. In this paper we describe a series of laboratory gas injection tests using the bentonite adopted for use in Japanese TRU disposal, as well as an attempted visualization of the gas migration path inside the bentonite used as a buffer. By building a conceptual model from the results of these tests, the characteristics of gas migration through to breakthrough for bentonite can now be better understood in the context of Japanese TRU disposal. Thanks to the outcome of this research project, advanced knowledge may be applied to the conceptualization of TRU waste disposal.

Characterization of a C O2 gas vent using various geophysical and geochemical methods

An understanding of gas migration along faults is important in many geologic research fields, such as geothermal exploration, risk assessment, and, more recently, the geologic storage of man-made carbon dioxide [Formula: see text]. If these gases reach the surface, they typically are discharged to the atmosphere from small areas known as gas vents. In a study of an individual gas vent located in the extinct Latera caldera, central Italy, near-surface geochemical and geophysical surveys were conducted to define the spatial distribution of gas-induced effects in the first few meters of the soil and, by inference, the 3D structure and geometry of the associated gas-permeable fault. Grid surveys and detailed profiles were performed across this vent using time-domain reflectometry (TDR), ground-penetrating radar (GPR), frequency-domain electromagnetics (FDEM), electrical resistivity tomography (ERT), and gas geochemistry measurements. Detailed profilesurveys indicate that the leaking [Formula: see text] has changed the physical, chemical, and biological soil environment of the vent, resulting in significant spatial variations in parameters (e.g., water content and soil electric/dielectric properties) that influence geophysical measurement results. Despite the strong difference in vertical and lateral resolution and depth of investigation, all methods show the same general trends and similar relative variations in the measured physical parameters. TDR and GPR data highlight anomalous shallow lateral variations, whereas FDEM and ERT measurements identify the vertical extension of the anomalous zone. All methods highlight a north-northwest–south-southeast anomaly alignment that we associate with the main fault; FDEM and, to a lesser extent, [Formula: see text] flux also show elongation orthogonal to this direction, implying that the vent may occur at the intersection of two structures. Thus, different near-surface geophysical and geochemical methods can provide important information on faults and their gas-migration characteristics.

軽石凝灰岩のガス移行特性に関する研究 （その２）気液二相流パラメータの同定

軽石凝灰岩のガス移行特性に関する研究 （その２）気液二相流パラメータの同定