The relationship between open, dry microcracks andPwave velocity of crystalline rocks: Application to in situ stress estimates on KTB drill cores after stress relaxation

The distribution of the non-uniform in situ stress around wellbore will impair the stability of the rock of wellbore wall. Drilling the underbalanced wells and depleted formations, the instability of the wellbore can result in the drilling failure. Mechanics model of the wellbore wall rock is developed. According to the relationship between the stress function and components of stresses, the superposition principle is adopted to develop the formulas of the radial, hoop, and shear stresses of the wellbore wall under the non-uniform in situ stress. The formula of the mud density which do not crash the rock of wellbore wall is derived. The error of the mud density between fitting formula developed in the paper and theoretical method is less than 2.5%. The mud density that ensure the stability of wellbore is determined.

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Stress, Microstructure, and Thermal Behavior in Mo/Si X-Ray Multilayers

MRS Proceedings ◽

10.1557/proc-382-297 ◽

1995 ◽

Vol 382 ◽

Cited By ~ 3

Author(s):

Tai D. Nguyen ◽

James H. Underwood

Keyword(s):

Thermal Stress ◽

Stress Relaxation ◽

Magnetron Sputtering ◽

Thermal Behavior ◽

Microstructural Evolution ◽

Intrinsic Stress ◽

Working Pressure ◽

X Ray ◽

The Relationship

ABSTRACTThe relationship between intrinsic stress and microstructural evolution in nanometer Mo/Si multilayers deposited by magnetron sputtering at low working pressure (2.5 mTorr) is studied. The stress depends strongly on the microstructure which evolves with the multilayer period. In-situ thermal stress measurements show stress relaxation is observed in Mo/Si multilayers after annealing at 300°C in nitrogen ambient, due to microstructural changes in the multilayers. Average stress exhibits changes after annealing at 500°C which correspond to increased interdiffusion between the layer materials and crystallization at the interfaces.

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Study on the Retention of Large Mining Height and Small Coal Pillar under Thick and Hard Roof of Bayangaole Coal

Advances in Civil Engineering ◽

10.1155/2021/8837189 ◽

2021 ◽

Vol 2021 ◽

pp. 1-17

Author(s):

Shankun Zhao ◽

Jianping Zuo ◽

Lei Liu ◽

Kaijun Wu

Keyword(s):

Coal Pillar ◽

Peak Stress ◽

In Situ Stress ◽

Economic Benefits ◽

Hard Roof ◽

Working Face ◽

Large Mining Height ◽

The Impact ◽

The Relationship

The coal pillar stress distribution at the 311102 working face in the Bayangaole Mine is analyzed and revealed. In addition, borehole stressmeter, PASSAT monitoring system, and numerical modelling are fully utilized. Based on the patterns of acoustic wave velocity distribution, it is discovered that the impact created by mining activity can expand into the working face around 40 m, where the peak stress concentration is found about 15 m ahead. According to borehole stressmeter readings, mildly impacted, ordinarily impacted, and severely impacted zones are distinguished. The equilibrium theory and corresponding calculation indicated that the coal body in front of the working face has a plastic zone width of 4.96 m. The stress-displacement analysis based on numerical simulation showed that the relationship between peak vertical stress and pillar width is unimodal and bimodal. Specifically, both 5 and 10 m wide pillars showed a unimodal stress-width correlation and the peak vertical stresses are all located at the pillar center, whereas 15 m wide pillar has a bimodal stress-width relationship. In comparison, 10 m wide pillar holds the maximum in-situ stress. In consideration of site conditions and economic influences, 6 m wide coal strip coal pillar is designed at the working face 311102. As a result, stopping was successfully completed, and remarkable economic benefits were achieved.

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