Evaluation of Stress-Controlled Permeability of Coal Fractures - A Laboratory Study

2013 ◽  
Vol 734-737 ◽  
pp. 703-708
Author(s):  
Yi Dong Cai ◽  
Da Meng Liu ◽  
Yan Bin Yao ◽  
Bai Ren Zhang ◽  
Jun Qian Li ◽  
...  
Keyword(s):  
Elastic Deformation ◽  
Axial Stress ◽  
Fractal Dimensions ◽  
Confining Pressure ◽  
Control Factor ◽  
Type I ◽  
Permeability Characteristics ◽  
Linear Elastic ◽  
Variable Permeability ◽  
Nonlinear Elastic

Experiments on coal permeability with saturated water under tri-axial stress were conducted. The relationship between stress and permeability under tri-axial stress was analyzed on the rock mechanical experimental rig (GAW-2000). After the experiments on permeability, the fracture characteristics were researched by X-ray computerized tomography, which shows that the bituminous coal normally has high fractal dimensions (generally over 1.8) and wide aperture. The results for permeability reveal that bituminous coals always have variable permeability characteristics under incremental axial stress due to its inherent fracture features. It can be divided into two types: type I, at the linear and nonlinear elastic deformation and peak stage, the permeability keeps rising, which is represented by FYGY8 #. The main control factor of permeability should be related to coal microfractures and coal compositions. Type II, which is represented by sample YCLZ2#, in the initial linear elastic stage, there is a decrease trend in the permeability performance, and then permeability gradually rise when it comes into the stage of nonlinear elastic deformation. The permeability will keep go down after coal becomes soften under the action of confining pressure, compaction.

scholarly journals Experimental study on permeability characteristics of gas-containing raw coal under different stress conditions

2018 ◽  
Vol 5 (7) ◽  
pp. 180558 ◽  
Author(s):  
Dongming Zhang ◽  
Yushun Yang ◽  
Hao Wang ◽  
Xin Bai ◽  
Chen Ye ◽  
...  
Keyword(s):  
Flow Rate ◽  
Coal Sample ◽  
Axial Stress ◽  
Axial Strain ◽  
Confining Pressure ◽  
Gas Pressure ◽  
Permeability Characteristics ◽  
Loading And Unloading ◽  
Unloading Confining Pressure ◽  
Function Relation

The present experimental study on permeability characteristics for raw coal under different stress states is implemented by applying the triaxial self-made ‘THM coupled with servo-controlled seepage apparatus for gas-containing coal’; the result indicates that the flow rate of gas in the coal sample gradually decreases with the nonlinear loading of axial pressure and increases with the nonlinear unloading of axial stress and confining pressure. The flow rate, axial stress and confining pressure curves all satisfy the negative exponential function relation. When the sample reaches the peak intensity, the sample will be destroyed and the stress will drop rapidly; then the flow rate of the sample will increase rapidly. At this stage, the flow rate and axial strain show an oblique ‘v' pattern. The flow rate of the coal sample increases nonlinearly with the increase of gas pressure; the relation curve between flow rate and gas pressure satisfies the power function relation. Under the same confining pressure and gas pressure conditions, the larger the axial stress, the smaller the flow rate of the coal sample. Under the same axial stress and gas pressure conditions, the flow rate of the coal sample will first decrease, but then increase as the confining pressure decreases. During the post-peak loading and unloading process, the flow rate of the coal sample will decrease with the loading of confining pressure but increase with the unloading of confining pressure, and there will be an increase in wave shape with the increase in axial strain. The flow rate of each loading and unloading confining pressure is higher than that of the previous loading and unloading confining pressure. At the post-peak stage, the relation curve between the flow rate of the coal sample and the confining pressure satisfies the power function relation in the process of loading and unloading confining pressure.

Poro-acoustoelasticity with compliant pores for fluid-saturated rocks

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. WC1-WC14 ◽  
Author(s):  
Bo-Ye Fu ◽  
Li-Yun Fu
Keyword(s):  
Elastic Deformation ◽  
Strain Energy ◽  
Dual Porosity ◽  
Velocity Variation ◽  
Energy Transformation ◽  
Linear Elastic ◽  
Dual Porosity Model ◽  
Velocity Variations ◽  
Nonlinear Elastic ◽  
Porosity Model

Stress-induced influences on elastic wave velocities include elastic and inelastic behaviors. In general, deformation of rocks is primarily linear elastic for small-magnitude stresses; such behavior can be predicted by the conventional poro-acoustoelasticity theory. On the contrary, large-magnitude stresses induce linear elastic deformation in stiff pores and rock grains and nonlinear elastic deformation in compliant pores. Conventional poro-acoustoelasticity combines the kinetic and strain energy functions via the Lagrange equation. This theory reveals the strain energy transformation of the stiff pores and rock grains for velocity variation. The dual-porosity model uses a semiempirical equation to express the influence of the nonlinear elastic deformation of compliant pores on velocity variations; however, this model does not include the strain energy transformation of compliant pores. We incorporate the dual-porosity model into the conventional poro-acoustoelasticity theory to account for linear and nonlinear elastic deformations through the strain energy transformation of rock grains, stiff pores, and compliant pores. We determine that the work of the loading stress is transformed into two parts: the strain energy for the linear elastic deformation of rock grains and stiff pores and the nonlinear elastic deformation of compliant pores. On applying this theory to ultrasonic measurements under different differential pressures for a saturated sandstone sample, we see that the resulting solution of stress-associated velocity variations is more precise than that obtained using the conventional poro-acoustoelasticity theory, especially in the low-effective-pressure regime.

scholarly journals Surface microstructures developed on polished quartz crystals embedded in wet quartz sand compacted under hydrothermal conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Peter M. Schutjens ◽  
Christopher J. Spiers ◽  
André Rik Niemeijer
Keyword(s):  
Quartz Sand ◽  
Axial Stress ◽  
Dissolution Kinetics ◽  
Confining Pressure ◽  
Pressure Solution ◽  
Hydrothermal Conditions ◽  
Quartz Crystals ◽  
Surface Microstructures ◽  
Quartz Aggregates ◽  
Intergranular Pressure

AbstractIntergranular pressure solution plays a key role as a deformation mechanism during diagenesis and in fault sealing and healing. Here, we present microstructural observations following experiments conducted on quartz aggregates under conditions known to favor pressure solution. We conducted two long term experiments in which a quartz crystal with polished faces of known crystallographic orientation was embedded in a matrix of randomly oriented quartz sand grains. For about two months an effective axial stress of 15 MPa was applied in one experiment, and an effective confining pressure of 28 MPa in the second. Loading occurred at 350 °C in the presence of a silica-saturated aqueous solution. In the first experiment, quartz sand grains in contact with polished quartz prism ($$\overline10{1 }0$$ 1 ¯ 010 ) faces became ubiquitously truncated against these faces, without indenting or pitting them. By contrast, numerous sand-grain-shaped pits formed in polished pyramidal ($$17\overline{6 }3$$ 17 6 ¯ 3 ) and ($$\overline{4 }134$$ 4 ¯ 134 ) crystal faces in the second experiment. In addition, four-leaved and (in some cases) three-leafed clover-shaped zones of precipitation formed on these prism faces, in a consistent orientation and pattern around individual pits. The microstructures observed in both experiments were interpreted as evidence for the operation of intergranular pressure solution. The dependence of the observed indentation/truncation microstructures on crystal face orientation can be explained by crystallographic control of stress-induced quartz dissolution kinetics, in line with previously published experimental and petrographic data, or possibly by an effect of contact orientation on the stress-induced driving force for pressure solution. This should be investigated in future experiments, providing data and microstructures which enable further mechanism-based analysis of deformation by pressure solution and the effect of crystallographic control on its kinetics in quartz-rich sands and sandstones.

scholarly journals The meso-fracturing mechanism of marble under unloading confining pressure paths and constant axial stress

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Linna Sun ◽  
Liming Zhang ◽  
Yu Cong ◽  
Yaduo Song ◽  
Keqiang He
Keyword(s):  
Shear Failure ◽  
Axial Stress ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Confining Pressures ◽  
Tension Cracks ◽  
Trial And Error Method ◽  
Unloading Confining Pressure ◽  
Fracturing Mechanism

AbstractFailure tests on marble during unloading confining-pressure under constant axial stress and simulations with the particle flow code were performed. The influence mechanism of the unloading rate of the confining pressure, initial unloading stress, and confining pressure on the failure characteristics of, and crack propagation in, marble was studied. By using the trial-and-error method, the conversion relationship between the unloading rates of confining pressures in laboratory tests and numerical simulations was ascertained. Micro-cracks formed in the unloading process of confining pressure are dominated by tension cracks, accompanied by shear cracks. The propagation of shear cracks lags that of tension cracks. As the confining pressure is increased, more cracks occur upon failure of the samples. The proportion of shear cracks increases while that of tension cracks decreases. The failure mode of samples undergoes a transition from shear-dominated failure to conjugated shear failure.

scholarly journals Experimental Study on Compression Deformation and Permeability Characteristics of Grading Broken Gangue under Stress

Processes ◽  
2018 ◽  
Vol 6 (12) ◽  
pp. 257 ◽  
Author(s):  
Yu Zhang ◽  
Wei Zhou ◽  
Ming Li ◽  
Zhanqing Chen
Keyword(s):  
Axial Stress ◽  
Compression Modulus ◽  
Raw Material ◽  
Compression Rate ◽  
Lateral Compression ◽  
Seepage Velocity ◽  
Permeability Characteristics ◽  
Backfill Mining ◽  
Important Test ◽  
Overlying Strata

As the important raw material for backfill mining, broken gangue’s deformation and permeability characteristics directly affect the deformation of the overlying strata above the filling space. In this paper, through lateral compression and pressed seepage tests, the deformation and permeability characteristics of broken gangue as a function of the stress level and grading features were studied. This research indicates that the stress of broken gangue increases exponentially with an increase in strain, and the compression modulus and compression rate present a positive correlation. The samples with discontinuous grading are more difficult to compress than the continuous grading samples, and the discontinuous grading samples are tighter in accordance with the increase in compression rate. At the same time, the change range of the seepage velocity and permeability of the broken gangue decreases. Positive correction between the grading index of the broken gangue and the effect of reducing the permeability of samples is more obvious under axial compression, and less axial stress is needed to achieve the same permeability level for discontinuous grading. This paper can provide an important test basis for the design of grading parameters and the prediction of filling effects of broken gangue on backfill mining.

On the Applicability of Sneddon's Solution for Interpreting the Indentation of Nonlinear Elastic Biopolymers

2014 ◽  
Vol 81 (9) ◽  
Author(s):  
Man-Gong Zhang ◽  
Jinju Chen ◽  
Xi-Qiao Feng ◽  
Yanping Cao
Keyword(s):  
Elastic Properties ◽  
Viscoelastic Properties ◽  
Contact Theory ◽  
Elastic Contact ◽  
Flat Punch ◽  
Linear Elastic ◽  
Contact Models ◽  
Properties Of Materials ◽  
Nonlinear Elastic ◽  
Viscoelastic Contact

Indentation has been widely used to characterize the mechanical properties of biopolymers. Besides Hertzian solution, Sneddon's solution is frequently adopted to interpret the indentation data to deduce the elastic properties of biopolymers, e.g., elastic modulus. Sneddon's solution also forms the basis to develop viscoelastic contact models for determining the viscoelastic properties of materials from either conical or flat punch indentation responses. It is worth mentioning that the Sneddon's solution was originally proposed on the basis of linear elastic contact theory. However, in both conical and flat punch indentation of compliant materials, the indented solid may undergo finite deformation. In this case, the extent to which the Sneddon's solution is applicable so far has not been systematically investigated. In this paper, we use the combined theoretical, computational, and experimental efforts to investigate the indentation of hyperelastic compliant materials with a flat punch or a conical tip. The applicability of Sneddon's solutions is examined. Furthermore, we present new models to determine the elastic properties of nonlinear elastic biopolymers.

scholarly journals Structural Design for a 10-GWh SMES Vacuum Vessel

1978 ◽  
Vol 100 (3) ◽  
pp. 263-270
Author(s):  
J. G. Bennett ◽  
C. A. Anderson
Keyword(s):  
Cylindrical Shell ◽  
Approximate Solution ◽  
Elastic Deformation ◽  
Material Properties ◽  
Structural Design ◽  
Shell Thickness ◽  
Construction Cost ◽  
Vacuum Vessel ◽  
Nonlinear Elastic

An approximate solution to the problem of the nonlinear elastic deformation of a periodically point-supported cylindrical shell is obtained. This solution is used to investigate the structural design of the vacuum vesssel for the large underground SMES concept. Vacuum vessel designs are evaluated by varying such parameters as shell thickness, support, spacing, material properties and physical configuration to keep the amount of material used and construction cost to a minimum.

scholarly journals Random Fiber Networks With Superior Properties Through Network Topology Control

2019 ◽  
Vol 86 (8) ◽  
Author(s):  
S. Deogekar ◽  
Z. Yan ◽  
R. C. Picu
Keyword(s):  
Network Architecture ◽  
Elastic Behavior ◽  
Fiber Networks ◽  
Linear Elastic ◽  
New Class ◽  
Link Density ◽  
Cross Link Density ◽  
Random Fiber Networks ◽  
Nonlinear Elastic ◽  
Poisson Contraction

In this work, we study the effect of network architecture on the nonlinear elastic behavior and strength of athermal random fiber networks of cellular type. We introduce a topology modification of Poisson–Voronoi (PV) networks with convex cells, leading to networks with stochastic nonconvex cells. Geometric measures are developed to characterize this new class of nonconvex Voronoi (NCV) networks. These are softer than the reference PV networks at the same nominal network parameters such as density, cross-link density, fiber diameter, and connectivity number. Their response is linear elastic over a broad range of strains, unlike PV networks that exhibit a gradual increase of the tangent stiffness starting from small strains. NCV networks exhibit much smaller Poisson contraction than any network of same nominal parameters. Interestingly, the strength of NCV networks increases continuously with an increasing degree of nonconvexity of the cells. These exceptional properties render this class of networks of interest in a variety of applications, such as tissue scaffolds, nonwovens, and protective clothing.

Comparison of Stress-Strain Relationships of FRP and Actively Confined High-Strength Concrete: Experimental Observations

2014 ◽  
Vol 919-921 ◽  
pp. 29-34 ◽  
Author(s):  
Jian Chin Lim ◽  
Togay Ozbakkloglu
Keyword(s):  
High Strength Concrete ◽  
Axial Stress ◽  
Axial Strain ◽  
High Strength ◽  
Confining Pressure ◽  
Confined Concrete ◽  
Lateral Strain ◽  
Stress Strain ◽  
Strength Concrete ◽  
Actively Confined Concrete

It is well established that lateral confinement of concrete enhances its axial strength and deformability. It is often assumed that, at a same level of confining pressure, the axial compressive stress and strain of fiber reinforced polymer (FRP)-confined concrete at a given lateral strain are the same as those in concrete actively confined concrete. To assess the validity of this assumption, an experimental program relating both types of confinement systems was conducted. 25 FRP-confined and actively confined high-strength concrete (HSC) specimens cast from a same batch of concrete were tested under axial compression. The axial stress-strain and lateral strain-axial strain curves obtained from the two different confinement systems were assessed. The results indicate that, at a given axial strain, lateral strains of actively confined and FRP-confined concretes correspond, when they are subjected to the same lateral confining pressure. However, it is observed that, at these points of intersections on axial strain-lateral strain curves, FRP-confined concrete exhibits a lower axial stress than the actively confined concrete, indicating that the aforementioned assumption is not accurate. The test results indicate that the difference in the axial stresses of FRP-confined and actively confined HSC becomes more significant with an increase in the level of confining pressure.

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