scholarly journals In-situ multiscale shear failure of a bistable composite tape-spring

2020 ◽  
Vol 200 ◽  
pp. 108348
Author(s):  
Bing Wang ◽  
Keith A. Seffen ◽  
Simon D. Guest ◽  
Tung-Lik Lee ◽  
Shi Huang ◽  
...  
Keyword(s):  
Shear Failure ◽  
Composite Tape

scholarly journals Mechanism of shear failure near fracture face during drainage process of CBM well

2018 ◽  
Vol 10 (8) ◽  
pp. 3309-3317
Author(s):  
Ping Xiong ◽  
Wang-shui Hu ◽  
Hai-xia Hu ◽  
Hailong Liu
Keyword(s):  
Coal Seam ◽  
Hydraulic Fracture ◽  
Shear Failure ◽  
Failure Envelope ◽  
Hole Pressure ◽  
Bottom Hole Pressure ◽  
Induced Stress ◽  
In Situ Stresses ◽  
Bottom Hole

Abstract In this paper, whether the coal fines can be induced by shear failure during drainage process has been discussed in detail. By coupling with the percolation theory, the elasticity mechanics were used to construe the extra stresses in the formation surrounding with the hydraulic fracture. The safe window of the bottom hole pressure was also calculated from the failure envelope. The research shows that the formation pressure on the fracture surface of the coal seam is negatively related with the bottom hole pressure, and the induced stress is positively related with the bottom hole pressure during the drainage process of fractured CBM wells. The pore pressure around the fracture changed due to pore-elastic effects, which also caused a significant change of the in situ stresses. In order to avoid the breakout of the coal seam around hydraulic fracture during drainage process, the model of the reasonable bottom hole pressure is also built.

DYNAMIC FAULT/FRACTURE SEAL BEHAVIOUR AND GEOMECHANICAL ANALYSIS OF THE GREATER GOBE AREA, SOUTHERN HIGHLANDS PROVINCE, PAPUA NEW GUINEA

2001 ◽  
Vol 41 (1) ◽  
pp. 251
Author(s):  
M.C. Daniels ◽  
D.T. Moffat ◽  
D.A. Castillo
Keyword(s):  
Papua New Guinea ◽  
Shear Failure ◽  
New Guinea ◽  
In Situ Stress ◽  
Stress Regime ◽  
Well Spacing ◽  
Geomechanical Analysis ◽  
Near Shore ◽  
Performance Results

The Gobe Main and SE Gobe Fields were discovered in the early 1990s in the Papuan Fold Belt in the Highlands of Papua New Guinea. Heavily karstified Darai Limestone at the surface and heli-supported drilling made field appraisal problematic and expensive. With initial well spacing upwards of several kilometres, these fields were thought to be ‘tank’ type models, with field-wide extrapolations of gas-oil and oil-water contacts.The main Iagifu Sandstone reservoir in the Gobe fields comprises several fluvial and near-shore sand bodies, which are readily correlatable across the fields. The reservoir units display discrete coarsening upward sequences containing medium (~17%) porosity, medium to high permeability (>100 mD) sandstones. Although several different depositional facies are interpreted within the Iagifu reservoir, sand units are extensive on the scale of the Gobe structures and do not appear to be producing significant lateral boundaries or reservoir compartmentalisation.Geomechanical analysis has enabled the calculation of in-situ stress magnitudes and establishment of a geomechanical model for Gobe. Locally, the Gobe Main Field appears to be in a strike-slip stress regime (SHmax>Sv>Shmin). SHmax directions vary from NNE– SSW to NE–SW. Stress magnitudes indicate the structure is near frictional equilibrium, with a high proportion of natural fractures and faults critically stressed for shear failure. Since first oil in early 1998, performance results have indicted pressure segregation of many of the wells in both the Gobe Main and SE Gobe fields. Although only one fault has been positively identified at the reservoir level, the mapped faults appear to have sand-on-sand juxtaposition with minimal (

Yielding and rupture in a lacustrine clay

1980 ◽  
Vol 17 (4) ◽  
pp. 559-573 ◽  
Author(s):  
A. Baracos ◽  
J. Graham ◽  
L. Domaschuk
Keyword(s):  
Shear Failure ◽  
Friction Angle ◽  
In Situ Stress ◽  
Grain Structure ◽  
Testing Procedures ◽  
Straight Line ◽  
Stress Levels ◽  
Lacustrine Clay ◽  
Field Behaviour

Recent tests have examined the properties of block samples and tube samples from depths to 12 m in Winnipeg clay. Careful trimming and a wide variety of testing procedures have permitted new insights into the behaviour of the clay that is markedly anisotropic and non-homogeneous. The effective strength envelope for "blue clay" from 6 to 12 m depth can be simplified into three straight-line sections. At low stresses, a section of the envelope has been identified having a low cohesion intercept and a high "friction" angle. This is thought to be caused by close Assuring in the clay, and controls the field behaviour in many small embankment, riverbank, and excavation problems. At in situ stress levels, the clay dilates markedly as failure is approached. Porewater pressures depend strongly on stress levels during laboratory reconsolidation. Residual strengths are low, and are influenced by the methods used during testing. Yielding has been clearly identified for shear failure of the grain structure, but is more poorly defined for increasing normal octahedral stresses. The work has emphasized the importance of selecting appropriate testing procedures and stresses for field applications.

scholarly journals Effective stresses and shear failure pressure from in situ Biot's coefficient, Hejre Field, North Sea

2016 ◽  
Vol 65 (3) ◽  
pp. 808-822 ◽  
Author(s):  
J.B. Regel ◽  
I. Orozova-Bekkevold ◽  
K.A. Andreassen ◽  
N.C. Høegh van Gilse ◽  
I.L. Fabricius
Keyword(s):  
North Sea ◽  
Shear Failure ◽  
Failure Pressure ◽  
Effective Stresses ◽  
Biot’S Coefficient

scholarly journals Texture and strength changes of buried surface-hoar layers with implications for dry snow-slab avalanche release

2000 ◽  
Vol 46 (152) ◽  
pp. 151-160 ◽  
Author(s):  
J. Bruce Jamieson ◽  
Jürg Schweizer
Keyword(s):  
Shear Strain ◽  
Crystal Size ◽  
Shear Failure ◽  
Field Measurements ◽  
Gravitational Energy ◽  
Strength Increase ◽  
Size Change ◽  
Buried Layers ◽  
Shear Frame

AbstractBuried layers of surface hoar are the failure plane for many slab avalanches, including fatal human-triggered avalanches in various mountain regions. These layers may persist as weak layers in the snow cover for weeks or months. It is therefore essential for operational avalanche forecasters to monitor the evolution of persistent weak layers, such as buried surface hoar. Traditional grain-shape observations of isolated grains with a magnifier and crystal screen do not show bonding that is decisive for strength. In this study we used in situ microphotography and observations of texture to complement strength measurements from shear frame tests. Buried layers of surface hoar consist of crystals most of which extend from the layer below to the layer above, and may exhibit a columnar or truss-like structure. Observations and measurements show that texture and crystal size change little over periods of up to several months during which the snowpack remains dry. Under these conditions, layer thickness decreases while density and strength increase. Based on field measurements, we argue that the increase in strength is primarily due to penetration of the surface-hoar crystals into the adjacent layers, especially at the bottom of the buried surface-hoar layer, where bonding is critical. The weak bonding at the bottom implies that shear failure occurs at the lower interface rather than within the weak layer. On slopes, we find that surface-hoar crystals that were initially surface-normal are tilted downslope faster than predicted by published shear strain rates for settled snow, indicating that shear strain is concentrated in these layers. The characteristic texture of buried surface hoar (columnar or truss-like) permits collapsing at the time of fracture. The gravitational energy released by the displacement of the slab may contribute to the extensive fracture propagation associated with buried surface-hoar layers.

scholarly journals Numerical Investigation of the Impacts of Borehole Breakouts on Breakdown Pressure

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 888 ◽  
Author(s):  
Hua Zhang ◽  
Shunde Yin ◽  
Bernt Aadnoy
Keyword(s):  
Hydraulic Fracturing ◽  
Shear Failure ◽  
In Situ Stress ◽  
Test Results ◽  
Breakdown Pressure ◽  
Borehole Breakout ◽  
Borehole Breakouts ◽  
The Difference ◽  
Mud Pressure

Borehole breakouts appear in drilling and production operations when rock subjected to in situ stress experiences shear failure. However, if a borehole breakout occurs, the boundary of the borehole is no longer circular and the stress distribution around it is different. So, the interpretation of the hydraulic fracturing test results based on the Kirsch solution may not be valid. Therefore, it is important to investigate the factors that may affect the correct interpretation of the breakdown pressure in a hydraulic fracturing test for a borehole that had breakouts. In this paper, two steps are taken to implement this investigation. First, sets of finite element modeling provide sets of data on borehole breakout measures. Second, for a given measure of borehole breakouts, according to the linear relation between the mud pressure and the stress on the borehole wall, the breakdown pressure considering the borehole breakouts is acquired by applying different mud pressure in the model. Results show the difference between the breakdown pressure of a circular borehole and that of borehole that had breakouts could be as large as 82% in some situations.

scholarly journals Investigation of the anisotropic confinement-dependent brittleness of a Utah coal

2020 ◽  
Author(s):  
Bo-Hyun Kim ◽  
Gabriel Walton ◽  
Mark K. Larson ◽  
Steve Berry
Keyword(s):  
Compressive Strength ◽  
Unconfined Compressive Strength ◽  
Shear Failure ◽  
Confining Stress ◽  
Included Angle ◽  
Anisotropic Strength ◽  
Brittle Ductile Transition ◽  
The Given ◽  
Compressive Tests

Abstract Changes of failure mechanism with increasing confinement, from extensional to shear-dominated failure, are widely observed in the rupture of intact specimens at the laboratory scale and in rock masses. In an analysis published in 2018, both unconfined and triaxial compressive tests were conducted to investigate the strength characteristics of 84 specimens of a Utah coal, including the spalling limits, the ratio of apparent unconfined compressive strength to unconfined compressive strength (UCS), the damage characteristics, and the post-yield dilatancy. These mechanical characteristics were found to be strongly anisotropic as a function of the orientation of the cleats relative to the loading direction, defined as the included angle. A total of four different included angles were used in the work performed in 2018. The authors found that the degree of anisotropic strength differed according to the included angle. However, the transition from extensional to shear failure at the given confinements was not clearly identified. In this study, a total of 20 specimens were additionally prepared from the same coal sample used in the previous study and then tested under both unconfined and triaxial compressive conditions. Because the authors already knew the most contrasting cases of the included angles from the previous work using the four included angles, they chose only two of the included angles (0° and 30°) for this study. For the triaxial compressive tests, a greater confining stress than the mean UCS was applied to the specimens in an attempt to identify the brittle-ductile transition of the coal. The new results have been compiled with the previous results in order to re-evaluate the confinement-dependency of the coal behavior. Additionally, the different confining stresses are used as analogs for different width-to-height (W/H) conditions of pillar strength. Although the W/H ratios of the specimens were not directly considered during testing, the equivalent W/H ratios of a pillar as a function of the confining stresses were estimated using an existing empirical solution. According to this relationship, the W/H at which in situ pillar behavior would be expected to transition from brittle to ductile is identified.

Prevention of Nanoscale Fines in Open-Hole Horizontal Coalbed Methane Wells During the Drainage Process

2021 ◽  
Vol 21 (1) ◽  
pp. 578-583
Author(s):  
Chunhua Guo ◽  
Yu Yang ◽  
Hansen Sun ◽  
Wangang Chen ◽  
Ping Yan ◽  
...  
Keyword(s):  
Coalbed Methane ◽  
Shear Failure ◽  
Model Parameters ◽  
Stress Model ◽  
Prediction Theory ◽  
Open Hole ◽  
Methane Desorption ◽  
Nanoscale Range ◽  
Coal Fines

Because coal is quite weak compared with conventional sandstone, shear failure downhole will produce a large amount of nanoscale coal fines during the drainage process. Since the size of pores in coal is on the nanoscale range, these fines will sometimes cause serious damage problems downhole. The origin of coal fines cannot be explained by conventional sand prediction theory, which was previously designed for conventional sandstone. During the drainage process, the in situ stress change in coal was caused by the combination of the poroelastic effect, methane desorption and compression around the borehole. To prevent nanoscale coal fines, the critical pressure drawdown can be predicted by the comprehensive stress model. A special test was also designed to determine the key model parameters, making the model easy to use. It was proven that the induced stress due to methane desorption can exaggerate the shear failure, which is different from conventional sand prediction theory. Based on the stress model, the safe window of bottom hole pressure was applied for open-hole horizontal wells to prevent the origin of nanoscale coal fines.

scholarly journals Lay-Up and Consolidation of a Composite Pipe by In Situ Ultrasonic Welding of a Thermoplastic Matrix Composite Tape

Materials ◽  
2018 ◽  
Vol 11 (5) ◽  
pp. 786 ◽  
Author(s):  
Riccardo Dell’Anna ◽  
Francesca Lionetto ◽  
Francesco Montagna ◽  
Alfonso Maffezzoli
Keyword(s):  
Matrix Composite ◽  
Ultrasonic Welding ◽  
Composite Tape ◽  
Thermoplastic Matrix ◽  
Composite Pipe
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