Evaluation of rock strength criteria for wellbore stability analysis

Stable evaluation of coal strength is needed in coal well-bore stability analysis. The regular analysis method of wellbore stability adopts Mohr-Coulomb strength criteria to judge the collapse pressure. Coal is dual porosity structure and contains joint fissures richly. Hoek-Brown criterion is much more reasonable to estimate the strength of jointed and fractured rock. So Hoek-Brown criterion is used to analyze the stability of multi-lateral horizontal coal bed methane well. Considering the GSI (geological strength index), structural and surface conditions of coal, the coal and rock mass strength parameters are converted into the underground coal mechanical parameters based on the triaxial test of intact coal. According to the stress state of multi-lateral horizontal well, the borehole collapse formulas are established based on Hoek-Brown Criterion. The effects on the wellbore stability, due to the joint fissures of coal, borehole size, drilling disturbance, are also discussed in this paper.

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Wellbore-Stability Analysis by Integrating a Modified Hoek-Brown Failure Criterion With Dual-Porochemoelectroelastic Theory (includes associated erratum)

SPE Journal ◽

10.2118/195685-pa ◽

2019 ◽

Vol 24 (05) ◽

pp. 1957-1981 ◽

Cited By ~ 1

Author(s):

Chao Liu ◽

Yanhui Han ◽

Hui–Hai Liu ◽

Younane N. Abousleiman

Keyword(s):

Stability Analysis ◽

Pore Pressure ◽

Failure Criterion ◽

Rock Strength ◽

Chemical Potential ◽

Wellbore Stability ◽

Natural Fracture ◽

Analysis Tool ◽

Drilling Mud

Summary When drilling through naturally fractured formations, the existence of natural fractures affects the fluid diffusion and stress distribution around the wellbore and induces degradation of rock strength. For chemically active formations, such as shale, the chemical–potential difference between the drilling mud and the shale–clay matrix further complicates the nonmonotonic coupled pore–pressure processes in and around the wellbore. In this work, we apply a recently formulated theory of dual–porosity/permeability porochemoelectroelasticity to predict the time evolution of mud–weight windows, while calculating stresses and pore pressure around an inclined wellbore drilled in a fractured shale formation. The effects of natural–fracture geometric and spatial distributions coupled with the chemical activity are considered in the wellbore–stability analysis. To account for the degrading effect of the fractured shale matrix on the bulk rock strength, a modified Hoek–Brown (MHB) criterion is developed to more closely describe the in–situ state of stress effects on the compressive shearing strength at great depth. Compared with the original Hoek–Brown (HB) failure criterion, the MHB criterion considers the influence of the intermediate principal stress and thus shows better agreement with true–triaxial data for various rocks at varying stress levels. The MHB criterion converges to the original HB criterion when the confining in–situ stresses are equal. Two field case studies indicate that this novel integrative methodology is capable of predicting the operational drilling–mud–weight windows used in these two cases. Another advantage of this newly developed technique is that it can be used as a back–analysis tool to estimate the fracture–matrix permeability from field operational data.

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Review of Methods for Uniaxial Compressive Rock Strength Estimation in Deepwater Formation With Uncertainty Quantification in Wellbore Stability Analysis in Absence of Core Measurements

10.2118/150343-ms ◽

2012 ◽

Cited By ~ 1

Author(s):

Rajeev Ranjan Kumar ◽

Dhiresh Govind Rao

Keyword(s):

Stability Analysis ◽

Uncertainty Quantification ◽

Rock Strength ◽

Wellbore Stability

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In-Situ Stresses, Rock Strength, Fluid Pressure, And Implications For Wellbore Stability And Oil And Gas Development In The Seboro and Tiaka Fields, Sulawesi, Indonesia

10.29118/ipa.0.12.e.073 ◽

2018 ◽

Author(s):

William Power

Keyword(s):

Oil And Gas ◽

Rock Strength ◽

Fluid Pressure ◽

Wellbore Stability ◽

Oil And Gas Development ◽

In Situ Stresses

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Wellbore Geomechanics of Extended Drilling Margin and Engineered Lost-Circulation Solutions

SPE Journal ◽

10.2118/185945-pa ◽

2017 ◽

Vol 22 (04) ◽

pp. 1178-1188 ◽

Cited By ~ 8

Author(s):

Amin Mehrabian ◽

Younane Abousleiman

Keyword(s):

Mechanical Properties ◽

Stability Analysis ◽

Analytical Approach ◽

Wellbore Stability ◽

Tensile Failure ◽

Mechanical Interaction ◽

Lost Circulation ◽

Drilling Operations ◽

Secondary Fractures ◽

Lost Circulation Materials

Summary Wellbore tensile failure is a known consequence of drilling with excessive mud weight, which can cause costly events of lost circulation. Despite the successful use of lost-circulation materials (LCMs) in treating lost-circulation events of the drilling operations, extensions of wellbore-stability models to the case of a fractured and LCM-treated wellbore have not been published. This paper presents an extension of the conventional wellbore-stability analysis to such circumstances. The proposed wellbore geomechanics solution revisits the criteria for breakdown of a fractured wellbore to identify an extended margin for the equivalent circulation density (ECD) of drilling. An analytical approach is taken to solve for the related multiscale and nonlinear problem of the three-way mechanical interaction between the wellbore, fracture wings, and LCM aggregate. The criteria for unstable propagation of existing near-wellbore fractures, together with those for initiating secondary fractures from the wellbore, are obtained. Results suggest that, in many circumstances, the occurrence of both incidents can be prevented, if the LCM blend is properly engineered to recover certain depositional and mechanical properties at downhole conditions. Under such optimal design conditions, the maximum ECD to which the breakdown limit of a permeable formation could be enhanced is predicted.

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