• Journal of the Korean Society of Safety
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• v.30 no.5
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• pp.37-43
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• 2015

This study examined the effects of the minimum horizontal load on the structural behaviors and safety of system supports. The minimum horizontal load was frequently ignored in the design of system supports even though the level of that load was specified in the code and guide in Korea such as 'Standard Specification in Temporary Construction' and 'Guide to Installation of Shores for a Concrete Bridge'. To examine the effects of considering the minimum horizontal load, the finite element analysis were performed for various system supports. By varying installing parameters of system supports such as the vertical member spacing, the installation height, and the thickness of slab, the maximum combined stress ratios were estimated to investigate the structural safety of system supports. The results showed similar axial stress in vertical members but an increase in bending stress with a consideration of the horizontal load. The combines stress ratios are remarkably increased due to the consideration of the horizontal load. Consequently, the system supports, which were initially estimated to be safe when only the vertical loads were considered, were changed to be unsafe in most cases by the effects of the both the vertical and horizontal stresses. Therefore, the minimum horizontal load following the code and the guide is an essential load that could control the structural safety of system supports.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.233-246
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• 2014

Estimation of fracture initiation pressure is one of the most difficult technical challenges in hydraulic fracturing treatment of vertical or horizontal oil wells. In this study, the influence of in-situ stresses and pore pressure values on fracture initiation pressure and its profile in vertical and horizontal oil wells in a normal stress regime have been investigated. Cohesive elements with traction-separation law (XFEM-based cohesive law) are used for simulating the fracturing process in a fluid-solid coupling finite element model. The maximum nominal stress criterion is selected for initiation of damage in the cohesive elements. The stress intensity factors are verified for both XFEM-based cohesive law and analytical solution to show the validation of the cohesive law in fracture modeling where the compared results are in a very good agreement with less than 1% error. The results showed that, generally by increasing the difference between the maximum and minimum horizontal stress, the fracture pressure and its profile has been strongly changed in the vertical wells. Also, it's been clearly observed that in a horizontal well drilled in the direction of minimum horizontal stress, the values of fracture pressure have been significantly affected by the difference between overburden pressure and maximum horizontal stress. Additionally, increasing pore pressure from under-pressure regime to over-pressure state has made a considerable fall on fracture pressure in both vertical and horizontal oil wells.

• Geomechanics and Engineering
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• v.34 no.1
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• pp.43-49
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• 2023

Knowledge of minimum horizontal stress (S_hmin) is a significant step in determining full stress tensor. It provides crucial information for the production of sand, hydraulic fracturing, determination of safe mud weight window, reservoir production behavior, and wellbore stability. Calculating the S_hmin using indirect methods has been proved to be awkward because a lot of data are required in all of these models. Also, direct techniques such as hydraulic fracturing are costly and time-consuming. To figure these problems out, this work aims to apply the long-short-term memory (LSTM) algorithm to S_hmin time-series prediction. 13956 datasets obtained from an oil well logging operation were applied in the models. 80% of the data were used for training, and 20% of the data were used for testing. In order to achieve the maximum accuracy of the LSTM model, its hyper-parameters were optimized significantly. Through different statistical indices, the LSTM model's performance was compared with with other machine learning methods. Finally, the optimized LSTM model was recommended for S_hmin prediction in the well logging operation.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.1
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• pp.187-194
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• 2002

It has been reported that cracks in mechanical joints is generally under mixed-mode and there is critical inclined angle at which mode I stress intensity factor becomes maximum. The crack propagates in arbitrary direction and thus the prediction of crack growth path is needed to provide against crack propagation or examine safety. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed far horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using stress intensity factor obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.187-192
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• 2001

Cracks in mechanical joints is generally under mixed-mode and there is the critical inclined angle at which mode I stress intensity factor becomes maximum. In order to evaluate the fatigue life of cracks in mechanical joints, horizontal crack normal to the applied load and located on minimum cross section is major concern but critical inclined crack must also be considered. In this paper mixed-mode fatigue crack growth test is performed for horizontal crack and critical inclined crack in mechanical joints. Fatigue crack growth path is predicted by maximum tangential stress criterion using mode I and mode II stress intensity factors obtained from weight function method, and fatigue crack growth rates of horizontal and inclined crack are compared.

• Geomechanics and Engineering
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• v.17 no.6
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• pp.535-541
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• 2019

Combining the radial well drilling and hydraulic fracturing technique, the production capacity of the reservoirs with low-permeability can be improved effectively. Due to the existence of radial holes, the stress around the well is redistributed, and the initiation and propagation of hydraulic fractures are different with those in traditional hydraulic fracturing. Therefore, it is necessary to study the influences of radial horizontal wells on hydraulic fracturing. The laboratory experiment was conducted to simulate the hydraulic fracturing on the physical model with radial holes. The experimental results showed that, compared with the borehole without radial holes, the sample with radial hole in the direction of maximum horizontal stress was fractured with significantly lower pressure. As the angle between direction of the horizontal hole and the maximum horizontal stress increased, the breakdown pressure grew. While when the radial hole was drilled towards the direction of the minimum horizontal stress, the breakdown pressure increased to that needed in the borehole without radial holes. When the angle between the radial hole and the maximum horizontal stress increase, the pressure required to propagate the fractures grew apparently, and the fracture become complex. Meanwhile, the deeper the radial hole drilled, the less the pressure was needed for fracturing.

• Geotechnical Engineering
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• v.14 no.5
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• pp.219-234
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• 1998

Modulus measurements in vertical boreholes under simulated horizontal in-situ stress conditions were performed on laboratory rock specimens. The experimental program was focused on the examination of modulus change with the variation of the orientation, magnitude and ratios of horizontal biaxial stresses. The experiment results show that the modulus increases when the magnitude of the horizontal stresses increases. The modulus measured in the minimum principal direction increased when the ratio between the horizontal principal stresses increased, while the modulus measured in the maximum principal direction decreased when the ratio of the horizontal principal stresses increased. These were caused by the tangential stresses that vary depending upon the magnitude of horizontal stresses, the applied pressure and the orientation of measurement. Also, the measured moduli were determined under tensile stress, compressive stress, or both stresses. Thus, the stress effect on deformation modulus should be considered, not only for the interpretation of the results of borehole deformability measurement, but also for the design of underground gas storage and pressure tunnel, and for the interpretation of tunnel monitoring.

• The Journal of Engineering Geology
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• v.17 no.2 s.52
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• pp.299-307
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• 2007

We collected data of hydraulic fracturing tests and overcoring tests conducted in 84 boreholes in the south-east Korea in order to analyze the contemporary state of stress in this region. The average direction of the maximum horizontal stress was determined to be $N66^{\circ}{\pm}31^{\circ}E$. The relative magnitudes of the three principal stresses was ${\sigma}_v$ (vertical stress) < ${\sigma}_h$ (minimum horizontal stress) < ${\sigma}_H$ (maximum horizontal stress), indicating thrust fault stress regime. The stress ratio K (horizontal stress/vertical stress) was relatively high (2.2

• Journal of Industrial Technology
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• v.24 no.A
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• pp.139-155
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• 2004

A room and pillar mining method has been adopting at the Jeungsun limestone mine. To check stability of pillar with multiple and irregular openings, the size, shape and spacing of rib pillar were first designed using some empirical suggestions. The Finite Difference Method(FDM)was used to analyze the pillar stability. Twelve different cases with the variation of K(horizontal/vertical stress)values, different height and different spacing of pillar were used in this study. Finally Mohr-Coulomb criterion was adopted to calculate the safety factors. Horizontal and vertical displacement, maximum and minimum principal stresses, range of plastic zone and safety factors were calculated at each case. As a result of analysis, the size of one block is 160m long, 70m wide, 40m high with 20m wide rib pillar and 20m square column pillar. The overall recovery at this case can be estimated about 40%.

• Geomechanics and Engineering
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• v.38 no.2
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• pp.107-123
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• 2024

The drilling angle of the well is an important factor that can affect the sand production process and make its destructive effects more severe or weaker. This study investigated the effect of different well angles on sand production for the Asmari Formation, located in one of the oil fields southwest of Iran. For this purpose, a finite difference model was developed for three types of vertical (90°), inclined (45°), and horizontal (0°) wells with casing and perforations in the direction of minimum and maximum horizontal stresses, then coupled with fluid flow. Here, finite element meshing was used, because the geometry of the model is so complex and the implementation of finite difference meshes is impossible or very difficult for such models. Using a combined FDM-FEM model with fluid flow, the sand production process in three different modes with different flow rates for the Asmari sandstone was investigated in this study. The results of numerical models show that the intensity of sand production is directly related to the in-situ stress state of the oil field and well drilling angle. Since the stress regime in the studied oil field is normal, the highest amount of produced sand was in inclined wells (especially wells drilled in the direction of minimum horizontal stress) and the lowest amount of sand production was related to vertical wellbore. Also, the Initiation time of sand production in inclined wells was much shorter than in other wellbores.