scholarly journals Influence of Stress and Crack Patterns on the Sensitive Characteristics of Fissure Sandstone Permeability under Hydromechanical Coupling

2019 ◽  
Vol 9 (4) ◽  
pp. 641 ◽  
Author(s):  
Gangwei Fan ◽  
Dongsheng Zhang ◽  
Shuai Zhang ◽  
Qiang Zhao ◽  
Wei Yu ◽  
...  
Keyword(s):  
Axial Stress ◽  
Rock Fracture ◽  
Confining Pressure ◽  
Rock Properties ◽  
Crack Model ◽  
Single Crack ◽  
Fracture Permeability ◽  
Fracture Characteristics ◽  
Hydraulic Aperture ◽  
Seepage Characteristics

The stress-sensitive of seepage characteristics after rock fracture has a crucial effect on the formation and closure of seepage channels, and it is important to study the sensitivity of fracture permeability for engineering seepage prevention. The aim of the current study was to investigate the permeability law of different fracture modes under unloading action. Firstly, the physical and mechanical parameters of the Voronoi polygon block and joint were fitted with rock properties obtained in the laboratory based on the fracture characteristics of triaxial seepage experiment samples. Crack reconstruction technology and a new hydraulic parameter fitting method were used to obtain the hydraulic aperture of microjoints and macrocracks. Then, six single crack models and four models based on typical fracture characteristics of rock samples were established to study the variation of the hydraulic aperture of microcracks and macroscopic cracks in unloading environment and the morphology of the main seepage passages, to explore the seepage characteristics of different angle cracks under different unloading stress paths, and to analyze the law of seepage variation of different crack forms under different stress environments. The results indicated that a horizontal hydraulic aperture is more sensitive to axial stress than a vertical hydraulic aperture and that a vertical hydraulic aperture is more sensitive to confining stress than a horizontal hydraulic aperture. For a single crack model, the sensitivity of a 70–90-degree crack to confining pressure is greater than that of a 40–60-degree crack. The axial stress sensitivity of a 40–60-degree crack is greater than that of a 70–90-degree crack. For a typical fracture model, under the same stress conditions, the sensitivity of four typical cracks to confining pressure is greater than that to axial pressure.

scholarly journals Experimental Study on Mechanical Properties and Seepage Laws of Raw Coal under Variable Loading and Unloading Rates

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-9
Author(s):  
Kangwu Feng ◽  
Kequan Wang ◽  
Dongming Zhang ◽  
Yushun Yang
Keyword(s):  
Axial Stress ◽  
Axial Strain ◽  
Radial Strain ◽  
High Sensitivity ◽  
Confining Pressure ◽  
Variable Loading ◽  
Axial Pressure ◽  
Unloading Rate ◽  
Loading And Unloading ◽  
Seepage Characteristics

This manuscript studied the effects of variable axial pressure loading rate and variable confining pressure unloading rate on the deformation behavior and seepage characteristics of raw coal under alternate loading and unloading of axial pressure and confining pressure. It believed that as axial stress increases, axial strain ε 1 decreases, radial strain ε 3 increases, and permeability k decreases, and ε 1 ′ , ε 3 ′ , and k ′ increase when confining pressure is decreases. With the loading of axial stress and the unloading of confining pressure, the variation amplitudes of ε 1 ′ , ε 3 ′ , and k ′ values reduce gradually. During axial stress loading, the rise in the amplitude of ε 1 is larger than that of ε 3 and the reduction in the amplitude of k , indicating that ε 1 is more sensitive to axial stress than ε 3 and k . During unloading of confining pressure, the increase rate of ε 3 is larger than that of ε 1 and k ; also, ε 3 showed a high sensitivity to confining pressure. In the stage of axial stress loading and confining pressure unloading, the evolution law of deformation and permeability parameters is basically consistent with the change in loading and unloading rate.

scholarly journals Experimental Study on Seepage Properties of Jointed Rock-Like Samples Based on 3D Printing Techniques

2020 ◽  
Vol 2020 ◽  
pp. 1-10 ◽  
Author(s):  
Wenhui Tan ◽  
Pengfei Wang
Keyword(s):  
3D Printing ◽  
Fractured Rock ◽  
Confining Pressure ◽  
Jointed Rock ◽  
Specimen Preparation ◽  
Fracture Permeability ◽  
Printing Technology ◽  
3D Printing Technology ◽  
Seepage Characteristics ◽  
Gap Width

Sample making of fractured rock mass is a big problem in rock mechanical test. The specimens prepared by traditional rock core drilling have some disadvantages such as unclear internal structure and great difference in mechanical properties; while, the samples prepared by inserting and seaming method have some other disadvantages such as hard to control the attitude of precast-joints, low accuracy. A method for preparing fractured rock-like samples based on 3D printing technology is introduced in this paper, and the seepage characteristics of fractured rock-like samples is studied by seepage experiments. Firstly, the standard profile curves of 10 grades of joint roughness are digitized and 10 groups of 3D digital fracture models are established with different roughness and thickness (i.e., 1.5, 3.0, and 5.0 mm, respectively). 30 fracture inserts are produced by 3D printing technology. Then, rock-like specimens with through-filling fractures are poured with molds. Finally, the permeability tests of the prepared rock-like specimens are carried out to study the seepage characteristics of fractures with different roughness and gap widths under different confining pressures. The results show that 3D printing technology provides an effective way for production of complex crack samples in laboratory test and the comparative analysis of tests. The seepage characteristics of fractures are well studied. When the gap width is small, the permeability decreases with the increase of roughness, and the influence of roughness on fracture permeability decreases rapidly with the increase of confining pressure and gap width. The permeability of through-filling fractures with different roughness and gap width decreases with the increase of confining pressure. The relationship between confining pressure and fracture permeability can be described by the power function. 3D printing technology overcomes the shortcomings of traditional specimen preparation methods and greatly improves the precision of crack inserts. The jointed rock-like model established by the method revealed the influence of fracture characteristics on seepage flow very well.

Experiment Study of Mechanical and Gas Seepage Characteristics of Containing-Gas Coal in the Process of Unloading Confining Pressure

2012 ◽  
Vol 524-527 ◽  
pp. 297-301
Author(s):  
Tao Deng ◽  
Jian Xin Tang ◽  
Jie Chen
Keyword(s):  
Axial Stress ◽  
Confining Pressure ◽  
Gas Permeation ◽  
Triaxial Stress ◽  
Experiment Study ◽  
Gas Seepage ◽  
Gas Coal ◽  
Seepage Characteristics ◽  
Unloading Confining Pressure

By using triaxial stress thermal-hydro-mechanical coal containing gas permeameter，mechanical and gas seepage characteristics is researched under different confining pressure、different initial axial stress and different unloading speed of confining pressure，the results shows that the increasing of unloading speed of confining pressure and the initial axial stress will shorten the time of the time of axial stress platform，From the aspect of gas permeation，the increasing of unloading speed of confining pressure and intial axial stress will accelerate the increasing of permeability，therefore， reasonable arrangement of roadway and method which can reduce the supporting stress should be proceed to preventing the outburst accident.

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 Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Zhiwei Cai ◽  
Tongqing Wu ◽  
Jian Lu ◽  
Yue Wu ◽  
Nianchun Xu
Keyword(s):  
Shear Crack ◽  
Rock Fracture ◽  
Confining Pressure ◽  
Particle Flow Code ◽  
Shear Cracks ◽  
Deformation And Failure ◽  
Fracture Development ◽  
Confining Pressures ◽  
The Law ◽  
Microcrack Growth

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.

scholarly journals The Analysis of a Cracked Material under Combined Unsymmetric Thermal Flux and Symmetric Linear Mechanical Loading

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
B. Wu ◽  
Q. A. Huang ◽  
D. Peng ◽  
X. Y. Yang ◽  
Z. Feng
Keyword(s):  
Mechanical Loading ◽  
Isotropic Material ◽  
Thermal Flux ◽  
Mode Ii ◽  
Crack Model ◽  
Single Crack ◽  
Permeable Crack ◽  
Fracture Parameters ◽  
Thermoelastic Field ◽  
The Fourier Transform

An improved partially permeable crack model is put forward to deal with the problem of a single crack embedded in an orthotropic or isotropic material under combined unsymmetric thermal flux and symmetric linear mechanical loading. With the application of the Fourier transform technique (FTT), the thermoelastic field is given in a closed form. Numerical results show combined unsymmetric linear thermal flux, symmetric linear mechanical loading, and dimensionless thermal conductivity, and the coefficient has influences on fracture parameters. For the improved partially permeable crack, the mode II stress intensity factor and the energy release rate might be zero or positive under combined unsymmetric thermal flux and symmetric linear mechanical loading. Therefore, closure of the crack tip region need not be considered under combined unsymmetric thermal flux and symmetric linear mechanical loading when making use of fracture parameters as a criterion.

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.

The Influence of Drying and Stress on the Permeability of Texas Lignite

1977 ◽  
Vol 99 (4) ◽  
pp. 634-640
Author(s):  
T. W. Thompson ◽  
S. Sen ◽  
K. E. Gray ◽  
T. F. Edgar
Keyword(s):  
Applied Stress ◽  
Significant Influence ◽  
Confining Pressure ◽  
Fracture Permeability ◽  
Gasification Process ◽  
Matrix Permeability ◽  
The Matrix ◽  
Order Of Magnitude ◽  
Permeability Increase

Tests have been carried out to quantify the variation in permeability of Texas lignite with drying and with applied stress. It has been shown that the matrix permeability of lignite may be increased from effectively zero to the order of 10 darcies by removing about 20 percent by weight of water. In addition, an increase of confining pressure after drying will reduce the permeability, but only by about one order of magnitude. Drying of the matrix thus may produce matrix permeabilities of the same order as the undried field fracture permeability. The permeability increase of the matrix is initially greater parallel to the bedding than perpendicular, but after further drying the two orientations show similar final permeabilities. This drying effect could have a significant influence on the operation of an in-situ gasification process by increasing the transmissivity and injectivity of the producing seam. Drying of the seam could occur by the flow of unsaturated gas and will be enhanced by combustion.

The effect of confining pressure on stress-drop in compressive rock fracture

1990 ◽  
Vol 175 (1-3) ◽  
pp. 237-248 ◽  
Author(s):  
I.A.H. Ismail ◽  
S.A.F. Murrell
Keyword(s):  
Stress Drop ◽  
Rock Fracture ◽  
Confining Pressure
Sign in / Sign up

Export Citation Format

Share Document