Effect of Eccentricity on Breakout Propagation around Noncircular Boreholes

Bahrehdar, Mohammad; Lakirouhani, Ali

doi:10.1155/2023/6962648

Cited by 4 publications

(2 citation statements)

References 38 publications

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“…Setiawan and Zimmerman (2022) presented a semi-analytical method to investigate the episodic breakout progression by means of the conformal mapping procedure, the analysis carried out by them led to a correlation between the breakout geometry and the in situ stresses. Bahrehdar and Lakirouhani (2023) investigated the effect of the eccentricity of the borehole on the breakout dimensions using the finite element method and concluded that for boreholes with different eccentricities, the stress concentration factor at the breakout tip becomes the same in the last step of expansion.…”

Section: Introductionmentioning

confidence: 99%

Failure Analysis Around Oriented Boreholes Using an Analytical Model in Different Faulting Stress Regimes

Lakirouhani

Ghorbannezhad

Medzvieckas

et al. 2023

Journal of Civil Engineering and Management

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One of the most important instabilities that may occur in a borehole is shear instability caused by high compressive stress in the borehole wall. The initial estimation of the width and depth of the failure zone around the borehole is very important in the field. In inclined boreholes, the shear instability or borehole breakout is affected by the in situ stress regime, the deviation angle of the borehole, the mechanical properties of the rock and the effect of the intermediate principal stress. In this article, an analytical model based on theory of elasticity is presented to find the breakout failure area around the inclined boreholes. Mogi-Coulomb shear failure criterion is used, in which there is also the effect of the intermediate principal stress. This model examines the failure in three-dimensional elements around the borehole for different in situ stress regime. The main finding of the analysis done in this article is that not only the deviation angle of the borehole but also the in situ stress regime has a great effect on the dimensions of the breakout. Also, the plane where the deviation angle of the borehole changes, affects the dimensions of the breakout.

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Section: Introductionmentioning

confidence: 99%

Failure Analysis Around Oriented Boreholes Using an Analytical Model in Different Faulting Stress Regimes

Lakirouhani

Ghorbannezhad

Medzvieckas

et al. 2023

Journal of Civil Engineering and Management

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“…Refs. [15][16][17] used numerical simulation to study the pressure relief effect under different drilling intervals and diameters. Based on the theory of energy propagation attenuation, Refs.…”

Section: Introductionmentioning

confidence: 99%

Numerical Simulation Analysis of Acoustic Emission Characteristics during the Drilling Pressure Relief Process in Coal Seams under Different Influencing Factors

Ma,

Li,

Zhang

et al. 2023

Processes

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Drilling pressure relief is a widely recognized and applied key technique to reduce the risk of rock burst occurrence, and its field-applied effects are also obvious. In this paper, the values of micro parameters required for discrete element method (DEM) simulations were first determined through indoor experiments and parameter calibration. Then, drilling pressure relief numerical simulations were conducted with different drilling diameters, drilling angles, and drilling depths. The results show that as the depth and diameter of the borehole increase, the peak strength of the coal sample first rapidly decreases, and then slowly decreases. The 30 mm depth and 14 mm diameter of the borehole are, respectively, the critical thresholds for the transition of the peak strength decrease rate; as the drilling angle increases, the peak strength of the coal sample first rapidly decreases and then increases, and the drilling angle of 25° is the critical threshold for the peak strength transformation. At the same time, the type of coal sample failure also changes from conjugate shear fracture to single slope shear fracture with the increase of three drilling parameters; shear and tensile cracks are the main types of micro fractures in coal samples. The research results are of great significance for improving the pressure relief plan of coal seam drilling and preventing and controlling rock burst disasters.

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Conflict Between Fracture Toughness and Tensile Strength in Determining Fracture Strength of Rock Samples with a Circular Hole

Lakirouhani,

Jolfaei

2024

Lecture Notes in Civil Engineering

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In this article, using a two-dimensional numerical model based on the finite element method, the fracture pressure of rock samples with a circular hole in the center is obtained. In this model, a mixed criterion is used to determine the fracture pressure, which is a combination of the tensile strength criterion and the fracture toughness criterion. The superiority of this model over the tensile strength criterion or the fracture toughness criterion is that it shows well the effect of the size of the hole in the middle of the sample on the fracture stress. The main and innovative finding of this article is that if the radius of the hole in the center of the sample is more than 70 mm, the fracture strength of the sample is dependent on the tensile strength of the rock material, and if the radius of the hole is less than 70 mm, the fracture strength is dependent on the fracture toughness. According to other results, the fracture strength decreases with the increase of the radius of the hole in the center of the sample, the decrease rate is high at first and then decreases with the increase of the radius of the hole.

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Effect of Eccentricity on Breakout Propagation around Noncircular Boreholes

Cited by 4 publications

References 38 publications

Failure Analysis Around Oriented Boreholes Using an Analytical Model in Different Faulting Stress Regimes

Failure Analysis Around Oriented Boreholes Using an Analytical Model in Different Faulting Stress Regimes

Numerical Simulation Analysis of Acoustic Emission Characteristics during the Drilling Pressure Relief Process in Coal Seams under Different Influencing Factors

Conflict Between Fracture Toughness and Tensile Strength in Determining Fracture Strength of Rock Samples with a Circular Hole

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