scholarly journals Study on Mesoscopic Stuctural Damage and Permeability Evolution of Freeze-Thaw Shale

Author(s):  
Jun-guang Wang ◽  
Zhang-qing Xuan ◽  
Qiao Jin ◽  
Wei-ji Sun ◽  
Bing Liang ◽  
...  

Abstract To study the mesoscopic damage and permeability evolution of rock under freezing-thawing (F-T) cycles, freezing-thawing cycle experiments were carried out on shale under different F-T temperatures and cycles, and nuclear magnetic resonance (NMR) and permeability experiments were conducted on shale after F-T. On the basis of the experiment, the pores and permeability of the F-T shale are analyzed, and the existing permeability model is modified and improved; Therefore, the mesoscopic damage evolution characteristics and permeability evolution law of the F-T shale are obtained. It is found that with the increase in the number of cycles, the pore structure of the rock samples changes as the pore size expands and the number of pores increases, and the average porosity also increases correspondingly. It is also found that there is a good positive correlation between the increase in shale porosity and the increase in permeability. Therefore, it is believed that the increase in pore size and pore number leads to an increase in porosity, which in turn leads to an increase in permeability. On the basis of the improved SDR permeability model, the spectral area ratio parameters of large pores and fractures in the T2 spectrum were added for correction, and the number of the F-T cycles and temperature parameters were introduced to obtain the modified permeability evolution model of F-T shale. Compared with the experimental results, it is found that the modified model has good applicability. The damage law and permeability of shale under different F-T conditions are analyzed from the microscopic point of view, which has important reference significance for engineering construction in frozen soil areas.

2019 ◽  
Vol 23 (3) ◽  
pp. 1611-1631 ◽  
Author(s):  
Ilari Lehtonen ◽  
Ari Venäläinen ◽  
Matti Kämäräinen ◽  
Antti Asikainen ◽  
Juha Laitila ◽  
...  

Abstract. Trafficability in forest terrain is controlled by ground-bearing capacity, which is crucial from the timber harvesting point of view. In winter, soil frost affects the most the bearing capacity, especially on peatland soils which have in general low bearing capacity. Ground frost similarly affects the bearing capacity of forest truck roads. A 20 cm thick layer of frozen soil or 40 cm thick layer of snow on the ground may already be sufficient for heavy forest harvesters. In this work, we studied the impacts of climate change on soil frost conditions and, consequently, on ground-bearing capacity from the timber harvesting point of view. The number of days with good wintertime bearing capacity was modelled by using a soil temperature model with a snow accumulation model and wide set of downscaled climate model data until the end of the 21st century. The model was calibrated for different forest and soil types. The results show that by the mid-21st century, the conditions with good bearing capacity will decrease in wintertime in Finland, most likely by about 1 month. The decrease in soil frost and wintertime bearing capacity will be more pronounced during the latter half of the century, when drained peatlands may virtually lack soil frost in most of winters in southern and western Finland. The projected decrease in the bearing capacity, accompanied with increasing demand for wood harvesting from drained peatlands, induces a clear need for the development of sustainable and resource-efficient logging practices for drained peatlands. This is also needed to avoid unnecessary harvesting damages, like rut formation on soils and damage to tree roots and stems.


2016 ◽  
Vol 11 (2) ◽  
pp. 12
Author(s):  
Mustafa Altındiş ◽  
Mustafa Güden ◽  
Chaoying Ni

<p>A sintered porous Ti<sub>6</sub>Al<sub>4</sub>V powder compact with a mean pore size of 63 μm and an average porosity of 37±1% was dip-coated at soaking times varying between 1- and 5-minute using a sol-derived calcium Hydrooxyapatite (HA) powder. The coated compacts were heat-treated at 840 <sup>o</sup>C. The coating thickness was found to increase with increasing soaking time, from 1.87 μm at 1-minute soaking to 9 μm at 5-minute soaking on the average. It was shown that at increasing soaking times, the originally open pores started to close, while at low soaking times the Ti<sub>6</sub>Al<sub>4</sub>V particles were partially coated. The coating layer was shown to be nanoporous and the depth of coating was observed to be relatively shallow: only few particles near the compact surface were HA-coated.</p>


2022 ◽  
Vol 29 (1) ◽  
pp. 12
Author(s):  
Yin Zeng ◽  
Lu Wang ◽  
Chaofu Deng ◽  
Qiangxing Zhang ◽  
Zhide Wu ◽  
...  

Energies ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 6323
Author(s):  
Xiaoping Li ◽  
Shudong Liu ◽  
Ji Li ◽  
Xiaohua Tan ◽  
Yilong Li ◽  
...  

Apparent gas permeability (AGP) is a significantly important parameter for productivity prediction and reservoir simulation. However, the influence of multiscale effect and irreducible water distribution on gas transport is neglected in most of the existing AGP models, which will overestimate gas transport capacity. Therefore, an AGP model coupling multiple mechanisms is established to investigate gas transport in multiscale shale matrix. First, AGP models of organic matrix (ORM) and inorganic matrix (IOM) have been developed respectively, and the AGP model for shale matrix is derived by coupling AGP models for two types of matrix. Multiple effects such as real gas effect, multiscale effect, porous deformation, irreducible water saturation and gas ab-/de-sorption are considered in the proposed model. Second, sensitive analysis indicates that pore size, pressure, porous deformation and irreducible water have significant impact on AGP. Finally, effective pore size distribution (PSD) and AGP under different water saturation of Balic shale sample are obtained based on proposed AGP model. Under comprehensive impact of multiple mechanisms, AGP of shale matrix exhibits shape of approximate “V” as pressure decrease. The presence of irreducible water leads to decrease of AGP. At low water saturation, irreducible water occupies small inorganic pores preferentially, and AGP decreases with small amplitude. The proposed model considers the impact of multiple mechanisms comprehensively, which is more suitable to the actual shale reservoir.


Author(s):  
Nao Fujimura ◽  
Hiroyuki Oguma ◽  
Takashi Nakamura

The effects of cyclic pre-strain on low cycle fatigue properties of austenitic stainless steel were investigated, and the fatigue damage was assessed based on several parameters such as the full width at half maximum (FWHM) of diffracted X-ray profile and surface roughness of specimens. The strain-controlled tests were conducted under strain ratio Rε = −1 and various constant total strain ranges. Also the change in remnant fatigue lives were investigated when the cyclic pre-strain were applied to the specimens under the different number of cycles which were determined with reference to the usage factor UFpre ranged from 0.2 to 0.8. As a result, the remnant fatigue life of the pre-strained samples became shorter than that of the sample without pre-strain as the UFpre increased. The relationship between the pre-strain damage expressed in UFpre and the remnant fatigue damage in UFpost was roughly described by the cumulative linear damage law: UFpre + UFpost = 1. Namely, the cyclic pre-strain affected the remnant fatigue lives. In order to evaluate the effects of cyclic pre-strain on fatigue lives more precisely, the damage in the cyclic pre-straining processes was estimated by using FWHM and surface roughness. The FWHM of the specimens with pre-strain once decreased with increase in UFpre, and then increased after showing a minimum value. The surface roughness of specimens increased linearly with an increase of the number of pre-straining cycles. These results suggested that the damage due to pre-strain can be assessed by means of FWHM and surface roughness of specimens.


2019 ◽  
Vol 9 (23) ◽  
pp. 5141
Author(s):  
Zhang ◽  
Wang ◽  
Du ◽  
Lou ◽  
Wang

In actual mining situations, the advancing speed of the working face is usually accelerated, which may affect the failure and seepage characteristics of gas-bearing coal, and may even induce dynamic disasters. In order to discover the effects of such accelerated advancement of the working face, an experimental study on the failure and seepage characteristics of gas-bearing coal under accelerated loading and unloading conditions was carried out in this work. The results showed that the energy release was more violent and impactful under accelerated loading and unloading paths. The time required for the failure of the sample was significantly shortened. After being destroyed, the breakup of the sample was more severe, and the magnitude of the permeability was greater. Accordingly, the acceleration of the loading and unloading had significant control effects on the failure and permeability of coal and it showed a significant danger of inducing coal and gas dynamic disasters. Meanwhile, the degree of influence of the acceleration on the coal decreased with an increase in the gas pressure and increased significantly with an increase in the initial confining pressure. It was found that for a deep high-gas mine, the accelerated advancement of the working face under a high in situ stress condition would greatly increase the risk of coal and gas dynamic disasters. Then, the permeability evolution model of gas-bearing coal in consideration of changes in the loading and unloading rates was theoretically established in this work, and this permeability model was validated by experimental data. The permeability model was found to be relatively reasonable. In summary, the effects of accelerated loading and unloading on the failure and seepage characteristics of gas-bearing coal were obtained through a combination of experimental and theoretical studies, and the intrinsic relationship between the accelerated advancement of the working face and the occurrence of coal and gas dynamic disasters was discovered in this work.


2001 ◽  
Vol 33 ◽  
pp. 333-338 ◽  
Author(s):  
P. J. Langhorne ◽  
V. A. Squire ◽  
C. Fox ◽  
T. G. Haskell

AbstractIt is well known that an incoming ocean swell produces a strain field in a land-fast ice sheet. The attenuation and spectral content of this strain field can be calculated and has been measured. The response of the sea ice to this type of cyclic forcing has also been measured, and in particular we are able to estimate the number of cycles to failure for sea ice loaded at constant amplitude. In this paper we consider the response of the land-fast ice sheet or vast floe to a measured ice-coupled wave field of variable amplitude. We use the Palmgren-Miner cumulative damage law and stress-lifetime curves taken from field experiments to predict the lifetime of the sea-ice sheet as a function of significant wave height and sea-ice brine fraction. Calculations are performed to account for the swell entering a land-fast sea-ice sheet at arbitrary angle, and the influence of c-axis alignment and the presence of pre-existing cracks are discussed.


1988 ◽  
Vol 110 (1) ◽  
pp. 243-249 ◽  
Author(s):  
A. Bejan

As an alternative to the mechanistic point of view expressed in Carathe´odory’s axioms, it is shown that the laws and concepts of thermodynamics are covered also by two statements made from a purely heat transfer perspective: Axiom I′—The heat transfer is the same in all zero-work processes that take a system from a given initial state to a given final state. Axiom II′—In the immediate neighborhood of every state of a system there are other states that cannot be reached from the first via a zero-work process. The primary concepts of this formulation are heat transfer, temperature, entropy, and zero-work boundary. Axiom I′ is used to define the property “energy,” and to deduce the secondary (derived) concept of “work transfer.” Axiom II′ is used to define the thermodynamic properties of “volume” and “pressure.” In this new heat transfer-based scheme, the analog of the Kelvin–Planck statement of the second law is: “∮δW < 0 is impossible” for an integral number of cycles executed by a closed system while in communication with no more than one pressure reservoir.


2020 ◽  
Vol 9 (2) ◽  
pp. 59-63
Author(s):  
S Neupane ◽  
T Pahari ◽  
N Lamichhane ◽  
DK Thapa

Introduction: MECT is a unique procedure where psychiatrist and anesthesiologist work together as a team. It is estimated that annually, approximately 1 million patients receive ECT worldwide. Due to association of physical complications like long bone and vertebrae fractures with direct ECT, anesthesia has been integrated into ECT. MECT is now the globally accepted standard mode of ECT. This study was done to see the Socio-demographic and clinical profile of patients receiving MECT. Material And Method: This is a hospital-based study done in BG hospital and Research Centre, Pokhara, Nepal for the duration of 12 months; from Baisakh, 2074 to Chaitra, 2074. A total of 50 consecutives cases that received MECT were enrolled after written informed consent for the ECT from the patients’ caretaker. The patient’s details, diagnosis and the numbers of cycles of MECT thus applied till clinical improvement were noted during the study period. MECT was administered on alternate days. The assessment of clinical improvement was done by the consultant psychiatrist. Following the protocol, each cycle of MECT was applied by consultant psychiatrist in the presence of the consultant anesthesiologist. Results: The total number of cases enrolled were 50. Out of 50 cases, 41 (82%) were male and mean age was 30.60 ± 10.13 years. The most common indications for MECT were BPAD (74%). The number of cycles of modified MECT applied on the individuals ranged from 6 to 18 cycles. Majority of the cases (78%) seem to have a clinical improvement after 6 cycles of modified ECT. There was no complication that warranted the termination of MECT. Conclusion: MECT when used judiciously is safe and leads to better clinical improvement.


Author(s):  
S. S. Volokhov ◽  
I. N. Nikitin ◽  
D. S. Lavrov

The results are described of the study of temperature deformation of different types of frozen soil in the cycles of cooling-heating at sudden change in temperature. The differences in the nature of the temperature deformation at step and one stage temperature change are shown. The dependences are investigated of the temperature deformation of frozen soils on soil type, moisture and total number of cycles of cooling-heating.


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