The impact of effective stress and gas slippage on coal permeability under cyclic loading

2016 ◽  
Vol 31 ◽  
pp. 236-248 ◽  
Author(s):  
Junpeng Zou ◽  
Weizhong Chen ◽  
Diansen Yang ◽  
Hongdan Yu ◽  
Jingqiang Yuan
Keyword(s):  
Cyclic Loading ◽  
Effective Stress ◽  
Coal Permeability ◽  
Gas Slippage ◽  
The Impact

Experimental research on coal permeability: The roles of effective stress and gas slippage

2014 ◽  
Vol 21 ◽  
pp. 481-488 ◽  
Author(s):  
Yong Li ◽  
Dazhen Tang ◽  
Hao Xu ◽  
Yanjun Meng ◽  
Junqian Li
Keyword(s):  
Experimental Research ◽  
Effective Stress ◽  
Coal Permeability ◽  
Gas Slippage

scholarly journals Micro-mechanical investigation of railway ballast behavior under cyclic loading in a box test using DEM: effects of elastic layers and ballast types

2019 ◽  
Vol 21 (4) ◽  
Author(s):  
Nishant Kumar ◽  
Bettina Suhr ◽  
Stefan Marschnig ◽  
Peter Dietmaier ◽  
Christof Marte ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Early Stage ◽  
Damage Model ◽  
Simulation Models ◽  
Railway Track ◽  
Maintenance Cost ◽  
Particle Movement ◽  
Railway Ballast ◽  
Elastic Layers ◽  
The Impact

Abstract Ballasted tracks are the commonly used railway track systems with constant demands for reducing maintenance cost and improved performance. Elastic layers are increasingly used for improving ballasted tracks. In order to better understand the effects of elastic layers, physical understanding at the ballast particle level is crucial. Here, discrete element method (DEM) is used to investigate the effects of elastic layers – under sleeper pad ($$\text {USP}$$USP) at the sleeper/ballast interface and under ballast mat ($$\text {UBM}$$UBM) at the ballast/bottom interface – on micro-mechanical behavior of railway ballast. In the DEM model, the Conical Damage Model (CDM) is used for contact modelling. This model was calibrated in Suhr et al. (Granul Matter 20(4):70, 2018) for the simulation of two different types of ballast. The CDM model accounts for particle edge breakage, which is an important phenomenon especially at the early stage of a tamping cycle, and thus essential, when investigating the impact of elastic layers in the ballast bed. DEM results confirm that during cyclic loading, $$\text {USP}$$USP reduces the edge breakage at the sleeper/ballast interface. On the other hand, $$\text {UBM}$$UBM shows higher particle movement throughout the ballast bed. Both the edge breakage and particle movement in the ballast bed are found to influence the sleeper settlement. Micro-mechanical investigations show that the force chain in deeper regions of the ballast bed is less affected by $$\text {USP}$$USP for the two types of ballast. Conversely, dense lateral forces near to the box bottom were seen with $$\text {UBM}$$UBM. The findings are in good (qualitative) agreement with the experimental observations. Thus, DEM simulations can aid to better understand the micro-macro phenomena for railway ballast. This can help to improve the track components and track design based on simulation models taking into account the physical behavior of ballast. Graphical Abstract

scholarly journals Evolution of Coal Permeability during Gas Injection—From Initial to Ultimate Equilibrium

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2800 ◽  
Author(s):  
Xingxing Liu ◽  
Jinchang Sheng ◽  
Jishan Liu ◽  
Yunjin Hu
Keyword(s):  
Effective Stress ◽  
Local Equilibrium ◽  
Fracture Aperture ◽  
Permeability Evolution ◽  
Full Spectrum ◽  
Coal Permeability ◽  
Fracture Pressure ◽  
Permeability Changes ◽  
Apparent Equilibrium ◽  
Non Equilibrium

The evolution of coal permeability is vitally important for the effective extraction of coal seam gas. A broad variety of permeability models have been developed under the assumption of local equilibrium, i.e., that the fracture pressure is in equilibrium with the matrix pressure. These models have so far failed to explain observations of coal permeability evolution that are available. This study explores the evolution of coal permeability as a non-equilibrium process. A displacement-based model is developed to define the evolution of permeability as a function of fracture aperture. Permeability evolution is tracked for the full spectrum of response from an initial apparent-equilibrium to an ultimate and final equilibrium. This approach is applied to explain why coal permeability changes even under a constant global effective stress, as reported in the literature. Model results clearly demonstrate that coal permeability changes even if conditions of constant effective stress are maintained for the fracture system during the non-equilibrium period, and that the duration of the transient period, from initial apparent-equilibrium to final equilibrium is primarily determined by both the fracture pressure and gas transport in the coal matrix. Based on these findings, it is concluded that the current assumption of local equilibrium in measurements of coal permeability may not be valid.

scholarly journals Effective stress regime around a jacked steel pile during installation ageing and load testing in chalk

2018 ◽  
Vol 55 (11) ◽  
pp. 1577-1591 ◽  
Author(s):  
R.M. Buckley ◽  
R.J. Jardine ◽  
S. Kontoe ◽  
B.M. Lehane
Keyword(s):  
Cyclic Loading ◽  
Effective Stress ◽  
Test Site ◽  
Static Tension ◽  
Load Testing ◽  
Stress Regime ◽  
Effective Stresses ◽  
Axial Cyclic Loading ◽  
Tension Testing ◽  
Static And Cyclic Loading

This paper reports experiments with 102 mm diameter closed-ended instrumented Imperial College piles (ICPs) jacked into low- to medium-density chalk at a well-characterized UK test site. The “ICP” instruments allowed the effective stress regime surrounding the pile shaft to be tracked during pile installation, equalization periods of up to 2.5 months, and load testing under static tension and one-way axial cyclic loading. Installation resistances are shown to be dominated by the pile tip loads. Low installation shaft stresses and radial effective stresses were measured that correlated with local cone penetration test (CPT) tip resistances. Marked shaft total stress reductions and steep stress gradients are demonstrated in the vicinity of the pile tip. The local interface shaft effective stress paths developed during static and cyclic loading displayed trends that resemble those seen in comparable tests in sands. Shaft failure followed the Coulomb law and constrained interface dilation was apparent as the pile experienced drained loading to failure, although with a lesser degree of radial expansion than with sands. Radial effective stresses were also found to fall with time after installation, leading to reductions in shaft capacity as proven by subsequent static tension testing. The jacked, closed-ended, piles’ ageing trends contrast sharply with those found with open piles driven at the same site, indicating that ageing is affected by pile tip geometry and (or) installation method.

scholarly journals Experimental investigation on the impact of coal fines generation and migration on coal permeability

2017 ◽  
Vol 159 ◽  
pp. 257-266 ◽  
Author(s):  
Tianhang Bai ◽  
Zhongwei Chen ◽  
Saiied M. Aminossadati ◽  
Thomas E. Rufford ◽  
Ling Li
Keyword(s):  
Experimental Investigation ◽  
Coal Permeability ◽  
And Migration ◽  
The Impact ◽  
Coal Fines

Coal permeability stimulation by NaClO oxidation

2019 ◽  
Vol 59 (2) ◽  
pp. 846
Author(s):  
Reydick Balucan ◽  
Zhenhua Jing ◽  
Jim Underschultz ◽  
Karen Steel
Keyword(s):  
Coal Seam ◽  
Structural Changes ◽  
Time Pressure ◽  
Fracture Aperture ◽  
Void Space ◽  
Coal Permeability ◽  
Core Flood ◽  
The Impact ◽  
Well Completions ◽  
Gas Bearing

Many prospective coal seams have limited permeability and are thus marginal for economic coal seam gas (CSG) extraction. To enhance seam permeability, various CSG stimulation techniques, including hydraulic fracturing, cavity well completions and horizontal wells, have been used commercially, but these techniques are not successful everywhere. Alternately, oxidant stimulation to enhance coal seam permeability may have potential benefit. In this paper, we report the oxidation of a cubic coal sample from the gas-bearing Bandanna Formation with 1% NaClO. Permeability variation were measured over time with core stimulation/flooding tests. Coal structural changes, captured via X-ray microcomputed tomography (µCT), were used to analyse and model the impact of oxidant stimulation on coal permeability. We found that NaClO stimulation was able to widen fracture aperture and generate additional cracks and/or void space. Analyses of the coal after reaction indicated improved pore connectivity. This resulted in a significantly higher permeability, as shown by both core flood tests and flow modelling/simulations using GeoDict’s FlowDict module. Although this paper confirms oxidant stimulation has the potential to improve coal seam permeability, the optimum volume and reaction time, pressure and temperature conditions and suitability for use in various coal types requires further research.

scholarly journals Experimental and Estimation Studies of Resilient Modulus of Marine Coral Sand under Cyclic Loading

2020 ◽  
Vol 8 (4) ◽  
pp. 287 ◽  
Author(s):  
Shao-Heng He ◽  
Qiong-Fang Zhang ◽  
Zhi Ding ◽  
Tang-Dai Xia ◽  
Xiao-Lu Gan
Keyword(s):  
Cyclic Loading ◽  
South China Sea ◽  
Effective Stress ◽  
South China ◽  
Stress Ratio ◽  
Resilient Modulus ◽  
Cyclic Stress ◽  
Marine Transportation ◽  
Cyclic Stress Ratio ◽  
Coral Sand

Coral sand is an important filler resource that can solve the shortage of terrestrial fillers in coastal areas. Recently, the foundations of many infrastructures in the South China Sea have been built with coral sand as fillers, which have been subjected to wave and traffic cyclic loads. Resilient modulus (Mr) is an important design parameter in marine engineering, but there are few studies on the resilient modulus response of coral sand under cyclic loading. A series of drained cyclic triaxial tests were carried out to investigate the effects of the initial mean effective stress (p0) and cyclic stress ratio (ζ) on the resilient modulus response of the coral sand from the South China Sea. The change of fractal dimension (αc) can reflect the rule of particle breakage evolution. The αc of coral sand shows a tendency of almost maintaining stable and then increasing rapidly with the increase of mean effective stress p0 under each cyclic stress ratio ζ. There is a threshold of p0, when the p0 exceeds this threshold, αc will increase significantly with the increase of p0. The increase of p0 has a beneficial effect on the improvement of the Mr, while the increase of ζ has both beneficial and detrimental effects on the improvement of the Mr. A new prediction model of the Mr considering particle breakage was established, which can better predict the Mr of coral sand in the whole stress interval. The research results can provide guidance for the design of marine transportation infrastructures, which can promote the development of marine transportation industry and energy utilization.

The influence of pore fluids and frequency on apparent effective stress behavior of seismic velocities

Geophysics ◽  
2010 ◽  
Vol 75 (1) ◽  
pp. N1-N7 ◽  
Author(s):  
Gary Mavko ◽  
Tiziana Vanorio
Keyword(s):  
Elastic Wave ◽  
Bulk Modulus ◽  
Effective Stress ◽  
High Frequency ◽  
Laboratory Data ◽  
Pore Fluids ◽  
Wave Velocities ◽  
Stress Behavior ◽  
Stress Coefficient ◽  
The Impact

Although poroelastic theory predicts that the effective stress coefficient equals unity for elastic moduli in monomineralic rocks, some rock elastic wave velocities measured at ultrasonic frequencies have effective stress coefficients less than one. Laboratory effective stress behavior for P-waves is often different than S-waves. Furthermore, laboratory ultrasonic velocities almost always reflect high-frequency artifacts associated with pore fluids, including an increase in velocities and flattening of velocity-versus-pressure curves. We have investigated the impact of pore fluids and frequency on the observed effective stress coefficient for elastic wave velocities by developing a model that calculates pore-fluid effects on velocity, including high-frequency squirt dispersion, and we have compared the model’s predictions with laboratory data. We modeled a rock frame with penny-shaped cracks for three situations: vacuum dry, saturated with helium, and saturated with brine. Even if the frame modulus depends only on the differential stress, the saturated-rock effective stress coefficient is predicted to be significantly less than one at ultrasonic frequencies because of two effects: an increase in the fluid bulk modulus with increasing pressure and the contribution of high-frequency squirt dispersion. The latter effect is most significant in soft fluids (helium in this experiment) in which the fluid-bulk modulus is less than or comparable to the thin-crack pore stiffness.

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