scholarly journals Experimental Research on Coal and Gas Delay Outburst and AE Characteristics under Conditions of Geostress and Gas Pressure Disturbance

2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Geng Jiabo ◽  
Liu Jiangtong ◽  
Li Xiaoshuang ◽  
Nie Wen ◽  
Zhang Dongming ◽  
...  
Keyword(s):  
Simulation System ◽  
Gas Pressure ◽  
Distinctive Features ◽  
Gas Accumulation ◽  
Low Intensity ◽  
Preparation Stage ◽  
Expansion Energy ◽  
Gas Expansion ◽  
Ae Signals ◽  
Dominant Parameter

Adopting yellow mud as barrier layer materials, coal and gas delay outburst experiments under conditions of geostress and gas accumulation disturbance were carried out by using self-developed simulation system, to find out roles of geostress and gas pressure played in the process of the delay outburst and ways to predict it, through analysis of variations of gas pressure, and AE characteristics during the process. The results show that after the geostress increased by 0.11 MPa from 1.80 MPa, an outburst occurs, while in gas accumulation situations, the gas pressure increase of 0.27 MPa from 0.67 MPa induces an outburst; hence, geostress is one of the dominant factors impacting an outburst occurrence. The lasting time of the outburst triggering under geostress disturbance is shorter than that under gas accumulation disturbance, while the duration of the outburst development under gas accumulation conditions is longer than that under geostress conditions. Coal seam breakage by geostress is the precondition for an outburst risk, and gas expansion energy is the dominant parameter influencing the duration of the outburst development. The AE signals show distinctive features in different stages of the outburst under geostress disturbance. At the preparation stage of the outburst, the AE signals increase sharply but have a low intensity and then drop to a lower balance level. At the triggering stage, the AE signals become active and increasing until up to the peak where the outburst occurs, and the intensity is highest.

scholarly journals Laboratory Study Phenomenon of Coal and Gas Outburst Based on a Mid-scale Simulation System

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Baisheng Nie ◽  
Yankun Ma ◽  
Shoutao Hu ◽  
Junqing Meng
Keyword(s):  
Internal Energy ◽  
Propagation Velocity ◽  
Strain Energy ◽  
Simulation System ◽  
Gas Pressure ◽  
Coal And Gas Outburst ◽  
Gas Outburst ◽  
Coal Particles ◽  
Expansion Energy ◽  
Gas Expansion

Abstract Outburst simulation experiments facilitate understanding coal and gas outburst in underground mining. With the help of the mid-scale simulation system, a model based on similitude principle, coal seam sandwiched by roof and floor, was constructed to conduct an outburst experiment. It had a three-dimensional size of 1500 mm × 600 mm × 1000 mm with 0.5 MPa gas pressure. The experimental procedures include specimen preparation, moulding, sealing, gas charging and adsorption, and completion. The outburst process was investigated by analyzing the gas pressure variation, temperature variation, outburst propagation velocity, particle size of outburst coal and energy transformation. During the experiment, each gas charging was accompanied with gas pressure or temperature fluctuation because of coal behavior of gas adsorption-desorption. The outburst propagation velocity was 17.2 m/s, obtained by a mass-weighted calculation of velocities of outburst coal. The small-size coal particles have a higher desorption rate and tend to participate in outburst process. According to energy conservation law, the energy forms of the outburst included elastic strain energy (Ee), gas expansion energy (Ep), internal energy of coal (ΔU), breakage work (W1), throwing out work (W2) and gas-flow loss energy (ΔE), and each was calculated respectively. Gas potential energy, including gas expansion energy and internal energy of coal, registered a larger percent and was far greater than the strain energy. And it can be the main factor influencing the occurrence of low-threshold outburst. The experimental system provides a feasible way to study the initiation and evolution of coal and gas outbursts.

scholarly journals Dynamic Characterization during Gas Initial Desorption of Coal Particles and Its Influence on the Initiation of Coal and Gas Outbursts

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1101
Author(s):  
Chaojie Wang ◽  
Xiaowei Li ◽  
Changhang Xu ◽  
Yujia Chen ◽  
Zexiang Tang ◽  
...  
Keyword(s):  
Pressure Gradient ◽  
Dynamic Effect ◽  
Coal Mass ◽  
Gas Pressure ◽  
Coal Surface ◽  
Dynamic Characterization ◽  
Coal Particles ◽  
Expansion Energy ◽  
Gas Expansion ◽  
Two Peaks

The law of gas initial desorption from coals is greatly important for understanding the occurrence mechanism and predicting coal and gas outburst (hereinafter referred to as ‘outburst’). However, dynamic characterization of gas initial desorption remains to be investigated. In this study, by monitoring the gas pressure and temperature of tectonically deformed (TD) coal and primary-undeformed (PU) coal, we established the evolution laws of gas key parameters during the initial desorption. The results indicate that the gas pressure drop rate, mass flow rate, initial desorption rate, and gas velocity increase with increasing gas pressure, with stronger gas dynamic effect, generating a high pressure gradient on the coal surface. Under the same gas pressure, the pressure gradient formed on the TD coal surface is greater than that formed on the surface of the PU coal, resulting in easily initiating an outburst in the TD coal. Moreover, the increased gas pressure increases temperature change rates (falling rate and rising rate) of coal mass. The minimum and final stable temperatures in the TD coal are generally lower compared to the PU coal. The releasing process of gas expansion energy can be divided into two stages exhibiting two peaks which increase as gas pressure increases. The two peak values for the TD coal both are about 2–3 times of those of the PU coal. In addition, the total gas expansion energy released by TD coal is far greater than that released by PU coal. The two peaks and the total values of gas expansion energy also prove that the damage of gas pressure to coal mass increases with the increased pressure, more likely producing pulverized coals and more prone to initiate an outburst.

scholarly journals Experimental Investigation on the Release Rule of the Gas Expansion Potential of Loaded Water-Filled Soft Coal

2019 ◽  
Vol 2019 ◽  
pp. 1-9
Author(s):  
Hengjie Qin ◽  
Jianping Wei ◽  
Donghao Li ◽  
Sen Li
Keyword(s):  
Water Content ◽  
Minimum Energy ◽  
Gas Pressure ◽  
Coal And Gas Outburst ◽  
Energy Evolution ◽  
Experimental Conditions ◽  
Gas Outburst ◽  
Minimum Energy Consumption ◽  
Expansion Energy ◽  
Gas Expansion

The aim of this study was to explore the evolution and release rule of internal energy storage in the process of coal and gas outburst and to further reveal the mechanism of coal and gas outburst from the perspective of energy. In this paper, the experiment of gas expansion energy release of coal samples under different adsorption pressures and with different moisture contents was carried out with the self-developed experimental device for release of gas-bearing coal expansion energy under load, and the energy of the whole outburst process was divided into three parts: the total expansion energy of gas, the energy consumed by destroying and throwing out coal body and the energy released inefficiently. On the basis of reasonable assumption, the energy evolution calculation model of each part was constructed with mathematical method. By analyzing the changes and distribution rules of three parts of energy under different experimental conditions, this paper explored the controlling effects of gas pressure, water content, and other variables on the energy evolution rules in the process of coal and gas outburst. Experimental and theoretical studies showed that in the gas-dominated coal and gas outburst process, the destruction of coal body was in the form of stratification; under each experimental condition, there existed a critical gas pressure value for the occurrence of coal and gas outburst, and there was a sudden change of energy evolution near this value; the existence of water made the critical pressure and the minimum energy consumption of coal and gas outburst increase obviously; under the experimental conditions, there was a linear relationship between the critical gas pressure and water content and a positive exponential relationship between the minimum energy consumption and water content.

scholarly journals Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-10
Author(s):  
Jie Cao ◽  
Qianting Hu ◽  
Yanan Gao ◽  
Minghui Li ◽  
Dongling Sun
Keyword(s):  
Diffusion Coefficient ◽  
Coal Seam ◽  
Volumetric Strain ◽  
Gas Pressure ◽  
Coal Seams ◽  
Distribution Law ◽  
Free Gas ◽  
Working Face ◽  
Expansion Energy ◽  
Gas Expansion

Due to the insufficient understanding of the outburst mechanism, the coal and gas outburst disasters in China are more serious. Gas expansion energy is the main source of energy that causes outburst. In order to explore the distribution law of gas expansion energy in outburst coal seams, a gas-solid coupling equation of outburst coal seams was established. The distribution law of coal stress field, deformation field, gas flow field, and gas expansion energy were simulated and analyzed by using COMSOL Multiphysics. The results showed that from the excavation face to the deep part of coal seam, the stress presented unloading zone, stress concentration zone, and original stress zone. The volumetric strain and permeability reached the minimum, while the gas pressure reached the maximum at the peak value of vertical stress. As time goes on, the gas pressure in the fracture near the working face gradually decreased and was less than the pressure in coal matrix. The total gas expansion energy consists of free gas and desorption gas expansion energy. Affected by the excavation, free gas expansion energy maintained a constant value in the original coal seam and gradually decreased in the area close to the working face. The expansion energy provided by desorption gas was zero in the original coal seam. And it first increased and then decreased rapidly near the working face. Compared with stress and coal seam thickness, gas pressure and initial diffusion coefficient had significant influence on gas expansion energy of coal seam. When the diffusion coefficient was greater than 1e-9 m2/s, the gas expansion energy of the coal seam near the working face was significantly higher than that of the original coal seam, which had the risk of inducing outburst.

Analysis of pulverized tectonic coal gas expansion energy in underground mines and its influence on the environment

2019 ◽  
Vol 27 (2) ◽  
pp. 1508-1520 ◽  
Author(s):  
Zhenyang Wang ◽  
Yuanping Cheng ◽  
Liang Wang ◽  
Chenghao Wang ◽  
Yang Lei ◽  
...  
Keyword(s):  
Underground Mines ◽  
Coal Gas ◽  
Tectonic Coal ◽  
Expansion Energy ◽  
Gas Expansion

scholarly journals Techno-Economic Assessment of Turboexpander Application at Natural Gas Regulation Stations

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 755 ◽  
Author(s):  
Szymon Kuczyński ◽  
Mariusz Łaciak ◽  
Andrzej Olijnyk ◽  
Adam Szurlej ◽  
Tomasz Włodek
Keyword(s):  
Natural Gas ◽  
Gas Flow ◽  
Electric Energy ◽  
Economic Assessment ◽  
Gas Pressure ◽  
Operational Parameters ◽  
Pressure Regulator ◽  
Correct Operation ◽  
Process Gas ◽  
Gas Expansion

During the natural gas pipeline transportation process, gas stream pressure is reduced at natural gas regulation stations (GRS). Natural gas pressure reduction is accompanied by energy dissipation which results in irreversible exergy losses in the gas stream. Energy loss depends on the thermodynamic parameters of the natural gas stream on inlet and outlet gas pressure regulation and metering stations. Recovered energy can be used for electricity generation when the pressure regulator is replaced with an expander to drive electric energy generation. To ensure the correct operation of the system, the natural gas stream should be heated, on inlet to expander. This temperature should be higher than the gas stream during choking in the pressure regulator. The purpose of this research was to investigate GRS operational parameters which influence the efficiency of the gas expansion process and to determine selection criteria for a cost-effective application of turboexpanders at selected GRS, instead of pressure regulators. The main novelty presented in this paper shows investigation on discounted payback period (DPP) equation which depends on the annual average natural gas flow rate through the analyzed GRS, average annual level of gas expansion, average annual natural gas purchase price, average annual produced electrical energy sale price and CAPEX.

Experiments and Simulations of Local Upstream Gas Accumulation Giving Unstable Production in a Flowline/Riser System

SPE Journal ◽  
2015 ◽  
Vol 20 (03) ◽  
pp. 598-609
Author(s):  
Tor Kindsbekken Kjeldby ◽  
Ole Jørgen Nydal
Keyword(s):  
Sensitivity Analyses ◽  
Small Scale ◽  
Unstable Flow ◽  
Good Correspondence ◽  
Flow Phenomenon ◽  
Gas Accumulation ◽  
Instability Phenomenon ◽  
Tracking Model ◽  
Gas Expansion ◽  
Stability Limits

Summary A set of small-scale air/water experiments has been carried out in a flowline/riser system to demonstrate how local gas accumulation in regions upstream from a riser or a well may give unstable flow, with cycling liquid production at the riser outlet. This unstable flow phenomenon differs from the well-known severe-slugging instability phenomenon in that the instability is driven by gas expansion in the riser, and not by expansion in the upstream pipeline. A Lagrangian slug tracking model was extended with the option of solving problems with entrained gas in slugs, and used to simulate the experiments. A simplified pressure/momentum scheme is applied. Sensitivity analyses were carried out for selected parameters. Good correspondence between experiments and simulations was found with respect to the period of the instability cycle for this gravity-dominated system. The experimental stability limits are also well reproduced.

scholarly journals The Meso-NH Atmospheric Simulation System. Part I: adiabatic formulation and control simulations

1998 ◽  
Vol 16 (1) ◽  
pp. 90-109 ◽  
Author(s):  
J. P. Lafore ◽  
J. Stein ◽  
N. Asencio ◽  
P. Bougeault ◽  
V. Ducrocq ◽  
...  
Keyword(s):  
Simulation System ◽  
General Description ◽  
Distinctive Features ◽  
Scale Down ◽  
System Part ◽  
Transport And Diffusion ◽  
File Manager ◽  
Grid Nesting ◽  
User Friendly ◽  
And Control

Abstract. The Meso-NH Atmospheric Simulation System is a joint effort of the Centre National de Recherches Météorologiques and Laboratoire d'Aérologie. It comprises several elements; a numerical model able to simulate the atmospheric motions, ranging from the large meso-alpha scale down to the micro-scale, with a comprehensive physical package, a flexible file manager, an ensemble of facilities to prepare initial states, either idealized or interpolated from meteorological analyses or forecasts, a flexible post-processing and graphical facility to visualize the results, and an ensemble of interactive procedures to control these functions. Some of the distinctive features of this ensemble are the following: the model is currently based on the Lipps and Hemler form of the anelastic system, but may evolve towards a more accurate form of the equations system. In the future, it will allow for simultaneous simulation of several scales of motion, by the so-called "interactive grid-nesting technique". It allows for the in-line computation and accumulation of various terms of the budget of several quantities. It allows for the transport and diffusion of passive scalars, to be coupled with a chemical module. It uses the relatively new Fortran 90 compiler. It is tailored to be easily implemented on any UNIX machine. Meso-NH is designed as a research tool for small and meso-scale atmospheric processes. It is freely accessible to the research community, and we have tried to make it as "user-friendly" as possible, and as general as possible, although these two goals sometimes appear contradictory. The present paper presents a general description of the adiabatic formulation and some of the basic validation simulations. A list of the currently available physical parametrizations and initialization methods is also given. A more precise description of these aspects will be provided in a further paper.

scholarly journals Study of the dynamics for gas accumulation in the annulus of production wells

2021 ◽  
Vol 250 ◽  
pp. 606-614
Author(s):  
Kamil Urazakov ◽  
Viktor Belozerov ◽  
Bulat Latypov
Keyword(s):  
Flow Rate ◽  
Flow Line ◽  
Gas Pressure ◽  
Time Interval ◽  
Gas Oil ◽  
Gas Accumulation ◽  
Technological Value ◽  
Rate Of Increase ◽  
Production Wells ◽  
Water Cut

Accumulation of associated petroleum gas in the annulus is one of the negative factors that impede the intensification of mechanized oil production. An increase in annular gas pressure causes growth of bottomhole pressure, a decrease in back pressure to the formation and the inflow of formation fluid. In addition, accumulation of gas in the annulus leads to displacement and a decrease in the liquid level above the submersible pump. Insufficient level of the pump submersion (rod or electric submersible) causes a number of complications in the operation of mechanized production units associated with overheating of the elements in pumping units. Therefore, the development of technologies for optimizing the gas pressure in the annulus is relevant. Method for calculating the intensity of gas pressure increase in the annulus of production wells operated by submersible pumps has been developed. Analytical dependence for calculating the time interval of gas accumulation in the annulus, during which the dynamic level decreases to the pump intake, is obtained. This value can be used to estimate the frequency of gas withdrawal from the annulus using compressors. It has been found that the rate of increase in annular gas pressure in time increases non-linearly with a rise in the gas-oil ratio and a decrease in water cut, and also linearly increases with a rise in liquid flow rate. Influence of the operating (gas-oil ratio) and technological (value of the gas pressure maintained in the annulus) factors on the flow rate of the suspended reciprocating compressor driven by the beam engine, designed for forced withdrawal and redirection of the annular gas into the flow line of the well is analyzed.

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