scholarly journals Evaluation of earthquake impact on magnitude of the minimum principal stress along a shotcrete lined pressure tunnel in Nepal

2019 ◽  
Vol 11 (5) ◽  
pp. 920-934 ◽  
Author(s):  
Krishna Kanta Panthi ◽  
Chhatra Bahadur Basnet
Keyword(s):  
Principal Stress ◽  
Pressure Tunnel ◽  
Minimum Principal Stress ◽  
Earthquake Impact

scholarly journals Numerical simulation on the simultaneous stress interference of parallel multiple hydraulic fractures

2021 ◽  
pp. 014459872110019
Author(s):  
Weiyong Lu ◽  
Changchun He
Keyword(s):  
Principal Stress ◽  
Hydraulic Fracture ◽  
Stress Ratio ◽  
Fracture Network ◽  
Hydraulic Fractures ◽  
Fracture Spacing ◽  
Induced Stress ◽  
Minimum Principal Stress ◽  
Fracturing Process ◽  
Stress Ratios

During horizontal well staged fracturing, there is stress interference between multiple transverse fractures in the same perforation cluster. Theoretical analysis and numerical calculation methods are applied in this study. We analysed the mechanism of induced stress interference in a single fracture under different fracture spacings and principal stress ratios. We also investigated the hydraulic fracture morphology and synchronous expansion process under different fracture spacings and principal stress ratios. The results show that the essence of induced stress is the stress increment in the area around the hydraulic fracture. Induced stress had a dual role in the fracturing process. It created favourable ground stress conditions for the diversion of hydraulic fractures and the formation of complex fracture network systems, inhibited fracture expansion in local areas, stopped hydraulic fractures, and prevented the formation of effective fractures. The curves of the maximum principal stress, minimum principal stress, and induced principal stress difference with distance under different fracture lengths, different fracture spacings, and different principal stress ratios were consistent overall. With a small fracture spacing and a small principal stress ratio, intermediate hydraulic fractures were difficult to initiate or arrest soon after initiation, fractures did not expand easily, and the expansion speed of lateral hydraulic fractures was fast. Moreover, with a smaller fracture spacing and a smaller principal stress ratio, hydraulic fractures were more prone to steering, and even new fractures were produced in the minimum principal stress direction, which was beneficial to the fracture network communication in the reservoir. When the local stress and fracture spacing were appropriate, the intermediate fracture could expand normally, which could effectively increase the reservoir permeability.

The Changing Rule of Rock Strength under True Triaxial Condition

2014 ◽  
Vol 522-524 ◽  
pp. 1410-1413
Author(s):  
Ze Kang Wen ◽  
Ke Min Wei ◽  
Jia Quan Hu ◽  
You Ling Fang
Keyword(s):  
Principal Stress ◽  
Rock Strength ◽  
Quadratic Function ◽  
Intermediate Principal Stress ◽  
Stress Effect ◽  
True Triaxial Test ◽  
True Triaxial ◽  
Minimum Principal Stress ◽  
Stress Coefficient ◽  
Intermediate Principal Stress Effect

The intermediate principal stress effect of the rock has been demonstrated. By analyzing true triaxial test results of Dunham dolomite and Mizuho trachyte, we studied relationship between minimum principal stress and the rock strength under the same intermediate principal stress coefficient, and the relationship between intermediate principal stress and the rock strength under the same minimum principal stress condition. Research shows that the minimum principal stress has a linear relation with the rock strength, the intermediate principal stress coefficient of a quadratic function relation with the rock strength. And the mathematic expression of the intermediate principal stress effect function was calculated.

scholarly journals Analytical Solution and Simulation of Oil Deliverability Analysis for Reorientation Hydraulic Fracture in Low-Permeability Reservoirs

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xinyu Qiu ◽  
Botao Kang ◽  
Pengcheng Liu ◽  
Shengye Hao ◽  
Yanglei Zhou ◽  
...  
Keyword(s):  
Analytical Solution ◽  
Principal Stress ◽  
High Water ◽  
Maximum Principal Stress ◽  
Low Permeability ◽  
Minimum Principal Stress ◽  
High Water Cut Stage ◽  
High Water Cut ◽  
Water Cut ◽  
Low Permeability Reservoirs

The hydraulic refracturing operations are often used to improve oil deliverability in the low-permeability reservoir. When the development of oilfields has entered a high water cut stage, oil deliverability can be promoted by refracturing reservoirs. The orientation of the new fracture formed by refracturing will be changed. The new formed fracture is called reorientation fracture. To calculate the oil deliverability of the refracture wells, a three-section fracture which includes reorientation fracture was established. The multiwell pressure drop superposition theory is used to derive the analytical solution of the refracture wells which includes the reorientation fracture. The numerical simulation was conducted to validate the results of the analytical solution. Comparing the refracture well deliverability of reorientation and nonreorientation, permeability, deflection angle, and the length of reorientation fracture will jointly control the productivity of refracture well. When the permeability in the direction of maximum principal stress is greater than the permeability in the direction of minimum principal stress, the capacity of reorientation fractures is relatively large. The deflection angles and the length of the reorientation fracture will directly affect the drainage area of the fracture, thus affecting productivity. The reorientation fractures generated by repeated fracturing have great potential for improving oil deliverability in the anisotropic low-permeability reservoirs.

scholarly journals Seepage Flow Properties of a Columnar Jointed Rock Mass in a True Triaxial Experiment

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Yanxin He ◽  
Zhende Zhu ◽  
Wenbin Lu ◽  
Yunjin Hu ◽  
Xinghua Xie ◽  
...  
Keyword(s):  
Rock Mass ◽  
Principal Stress ◽  
Jointed Rock ◽  
Jointed Rock Mass ◽  
Intermediate Principal Stress ◽  
True Triaxial ◽  
Minimum Principal Stress ◽  
Baihetan Hydropower Station ◽  
Columnar Jointed Rock Mass ◽  
Seepage Characteristics

A columnar jointed rock mass is a type of rock mass with strong geometric anisotropy and high interface permeability. Its seepage characteristics pose new challenges to the construction and maintenance of the Baihetan Hydropower Station on the Jinsha River. The research object in this study is the columnar jointed rock mass (basalt) in the dam area of Baihetan Hydropower Station. Similar-material model samples of the columnar jointed rock mass with different column dip angles ( α = 0 ° ~90°) were prepared following a similar principle. A true triaxial seepage–stress coupling test was conducted to evaluate the seepage characteristics of similar-material samples with different dip angles under intermediate principal stress and minimum principal stress. The experimental results showed that the columnar jointed rock mass exhibited apparent seepage anisotropy. The relationship curve between the volume flow rate Q and the pressure gradient − d P / d L of the samples with different dip angles showed evident nonlinear seepage under intermediate principal stress, which could be well expressed using the Forchheimer equation. It shows the characteristics of a typical linear Darcy flow under minimum principal stress. The law of variations in the permeability of the samples with different dip angles under intermediate principal stress can be well expressed using the one-dimensional quadratic function equation k = a + b σ 2 + c σ 2 2 , and the law of variations in the permeability of the samples with different dip angles under minimum principal stress can be well expressed using the logarithmic function k = a + b ln σ 3 . The permeabilities of the columnar jointed rock mass with dip angles of 0°, 15°, 30°, and 60° were most sensitive to changes in stress, and the seepage characteristics increased in complexity after changes in stress.

A review of methods for determining stress fields from earthquakes focal mechanisms; Application to the Sierentz 1980 seismic crisis (Upper Rhine graben)

2013 ◽  
Vol 184 (4-5) ◽  
pp. 319-334 ◽  
Author(s):  
Julie Maury ◽  
François H. Cornet ◽  
Louis Dorbath
Keyword(s):  
Stress Field ◽  
Principal Stress ◽  
Confidence Level ◽  
Focal Mechanisms ◽  
Upper Rhine Graben ◽  
Earthquake Focal Mechanisms ◽  
Rhine Graben ◽  
Minimum Principal Stress ◽  
Stress Directions ◽  
Upper Rhine

Abstract The inversion of earthquake focal mechanisms is one of the few tools available for determining principal stress directions at seismogenic depths. Various methods have been proposed for performing such inversions. For three of the most commonly used methods, including one that has been proposed by Jacques Angelier, we discuss the physical assumptions and the error determination and then we propose an extension for one of the methods. All four methods are then applied for evaluating the stress field in the Upper Rhine graben. They are applied to seismic data recorded with a temporary monitoring network that was deployed 12 hours after the magnitude Mw = 4.4 Sierentz earthquake, which occurred on July 15, 1980. While differences in principal stress directions can be as much as 28° depending on the method used for the principal stress direction determination (orientation of the minimum principal stress has been found to range from N051°E with a 27° plunge to N090° E with a 20° plunge), the 90% confidence level associated with each method varies from 11° to 27°. Moreover, these various methods yield fairly diverse values for the R factor that characterizes relative differences between principal stress magnitudes (from R = 0.7 with a 0.2 90% confidence level to R = 0.3 with a 0.2 90% confidence level). Furthermore all three methods leave some focal mechanisms unexplained. These are then declared to be the result of heterogeneity and are not considered for the inversion. It is concluded that earthquake focal mechanisms inversions lack resolution for stress field evaluation at depth if no proper attention is given to the event independence hypothesis. When proper attention is given to this hypothesis, a resolution of the order of 15° may be achieved. The minimum principal stress orientation derived with these various focal mechanisms inversions differs by 4 to 36° from the orientation determined from borehole breakouts observed in Basel, in a 5 km deep well (N054°E ± 14°), located some 20 km from Sierentz. The solution that fits best borehole breakout observations is that which satisfies the minimum number (three) of prerequisite physical assumptions.

Experimental study on the damage process of marble under true triaxial pre-peak unloading conditions

2021 ◽  
pp. 105678952110207
Author(s):  
Yaohui Gao ◽  
Zhaofeng Wang
Keyword(s):  
Cyclic Loading ◽  
Principal Stress ◽  
Stress Test ◽  
Tensile Failure ◽  
Dissipated Energy ◽  
Rock Damage ◽  
Rock Fracturing ◽  
True Triaxial ◽  
Minimum Principal Stress ◽  
Fracturing Process

Stress-induced instability is associated with rock damage. Here, the progressive brittle fracturing process in Jinping marble is studied by introducing two types of true triaxial pre-peak unloading tests, namely, the incrementally cyclic loading-unloading minimum principal stress test (ICM test) and the incrementally cyclic loading-unloading maximum and minimum principal stress test (ICMM test). By comprehensively analysing the irreversible strains, dissipated energy, acoustic emission (AE) characteristics and scanning electron microscopy (SEM) results, the rock damage evolution can be quantified and divided into two distinctive damage stages. At the boundary point, the irreversible strain increments reach their minimum values. In the gentle damage stage, the normalized irreversible strains increase linearly, and this process is associated with a small number of AE hits with low amplitude. The rapid damage stage is characterized by a nonlinear increase in the normalized irreversible strains, and this process is associated with a large number of AE hits with high amplitude. The dissipated energy mainly increases in the rapid damage stage. In addition, the rapid damage stage in the ICMM test mainly occurs in the last five cycles, due to the differences in the deviatoric stresses in each cycle. In both of these tests, the failure mode is principally characterized by tensile failure. Moreover, the precursory signals of rock fracturing and the influence of the loading paths on the strength are discussed.

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