New Analytical Model for Predicting the Unstable Zone Around the Borehole

SPE Journal ◽  
2014 ◽  
Vol 19 (06) ◽  
pp. 1177-1183 ◽  
Author(s):  
Mohamad Heidarian ◽  
Hossein Jalalifar ◽  
Mahin Schaffie ◽  
Saeed Jafari
Keyword(s):  
Numerical Methods ◽  
Plastic Zone ◽  
Numerical Solution ◽  
Analytical Model ◽  
Failure Criterion ◽  
Field Data ◽  
Drilling Mud ◽  
Underbalanced Drilling ◽  
Coulomb Failure ◽  
Coulomb Failure Criterion

Summary In this study, a new analytical model, which is computationally lower in cost than current numerical methods, is presented to calculate the radius of the plastic zone around the borehole in underbalanced drilling (UBD) to prevent borehole instability. With this model, it is also possible to analytically calculate the optimal drilling-mud weight, which is the amount of mud weight with no plastic zone. The presented model is based on the Mouhr-Coulomb failure criterion. The model can be used in both vertical and inclined wells and in poroelastic formations with anisotropic horizontal stresses. Predictions from the model provide a reasonable match to the field data and numerical solution results.

scholarly journals The Mohr–Coulomb criterion for intact rock strength and friction – a re-evaluation and consideration of failure under polyaxial stresses

Solid Earth ◽  
2016 ◽  
Vol 7 (2) ◽  
pp. 493-508 ◽  
Author(s):  
Abigail Hackston ◽  
Ernest Rutter
Keyword(s):  
Friction Coefficient ◽  
Failure Criterion ◽  
Fault Plane ◽  
Stress Conditions ◽  
Intact Rock ◽  
Rock Types ◽  
State Dependent ◽  
Failure Envelopes ◽  
Coulomb Failure ◽  
Coulomb Failure Criterion

Abstract. Darley Dale and Pennant sandstones were tested under conditions of both axisymmetric shortening and extension normal to bedding. These are the two extremes of loading under polyaxial stress conditions. Failure under generalized stress conditions can be predicted from the Mohr–Coulomb failure criterion under axisymmetric shortening conditions, provided the best form of polyaxial failure criterion is known. The sandstone data are best reconciled using the Mogi (1967) empirical criterion. Fault plane orientations produced vary greatly with respect to the maximum compressive stress direction in the two loading configurations. The normals to the Mohr–Coulomb failure envelopes do not predict the orientations of the fault planes eventually produced. Frictional sliding on variously inclined saw cuts and failure surfaces produced in intact rock samples was also investigated. Friction coefficient is not affected by fault plane orientation in a given loading configuration, but friction coefficients in extension were systematically lower than in compression for both rock types. Friction data for these and other porous sandstones accord well with the Byerlee (1978) generalization about rock friction being largely independent of rock type. For engineering and geodynamic modelling purposes, the stress-state-dependent friction coefficient should be used for sandstones, but it is not known to what extent this might apply to other rock types.

Establishment of a Dynamic Mohr–Coulomb Failure Criterion for Rocks

2012 ◽  
Vol 13 (1) ◽  
Author(s):  
Sheng Huang ◽  
Kaiwen Xia ◽  
Feng Dai
Keyword(s):  
Tensile Strength ◽  
Compressive Strength ◽  
Shear Strength ◽  
Failure Criterion ◽  
Dynamic Range ◽  
Split Hopkinson Pressure Bar ◽  
Rock Properties ◽  
Hopkinson Pressure Bar ◽  
Coulomb Failure ◽  
Coulomb Failure Criterion

AbstractStatic Mohr–Coulomb Failure Criterion for rocks has been used extensively in various rock engineering applications. In this model, the compressive strength, tensile strength, and shear strength are related. To investigate the applicability of the Mohr–Coulomb model to dynamic failures, we studied the correlation of the three dynamic rock properties: compressive strength, tensile strength and punch shear strength. The strengths are quantified using a split Hopkinson pressure bar (SHPB) system. The methods for acquiring these strengths were briefly discussed. A fine-grained sandstone, Longyou sandstone (LS) was studied using these methods. The results showed that the compressive strength calculated from the punch shear strength of LS matched well with the experimental UCS results, thus the punch shear strength could be effectively used to predict the UCS of rocks. The tensile strength calculated from the punch shear strength of LS also has exhibited a good trend with the experimental results of Brazilian tensile strength. We concluded that the famous Mohr–Coulomb criterion can be extended to the dynamic range. However, caution has to be taken in determining the loading rates for different strength results.

scholarly journals Three-Dimensional Numerical Analysis of the Tunnel for Polyaxial State of Stress

2015 ◽  
Vol 2015 ◽  
pp. 1-8
Author(s):  
Wenge Qiu ◽  
Chao Kong ◽  
Kai Liu
Keyword(s):  
Numerical Simulation ◽  
Mechanical Behavior ◽  
Principal Stress ◽  
Failure Criterion ◽  
Rock Strength ◽  
Strength Criterion ◽  
Intermediate Principal Stress ◽  
State Of Stress ◽  
Coulomb Failure ◽  
Coulomb Failure Criterion

The aim of this study is to have a comprehensive understanding of the mechanical behavior of rock masses around excavation under different value of intermediate principal stress. Numerical simulation was performed to investigate the influence of intermediate principal stress using a new polyaxial strength criterion which takes polyaxial state of stress into account. In order to equivalently substitute polyaxial failure criterion with Mohr-Coulomb failure criterion, a mathematical relationship was established between these two failure criteria. The influence of intermediate principal stress had been analyzed when Mohr-Coulomb strength criterion and polyaxial strength criterion were applied in the numerical simulation, respectively. Results indicate that intermediate principal stress has great influence on the mechanical behavior of rock masses; rock strength enhanced by intermediate principal stress is significant based on polyaxial strength criterion; the results of numerical simulation under Mohr-Coulomb failure criterion show that it does not exert a significant influence on rock strength. Results also indicate that when intermediate principal stress is relatively small, polyaxial strength criterion is not applicable.

Sign in / Sign up

Export Citation Format

Share Document