Influence of borehole diameter on the formation of borehole breakouts in black shale

Meier, T.; Rybacki, E.; Reinicke, Andreas; Dresen, Georg

doi:10.1016/j.ijrmms.2013.03.012

Cited by 87 publications

(43 citation statements)

References 33 publications

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“…Note that the borehole diameters of samples PN1 and PN2 were 6 and 10 mm, respectively. Interpolation of P* between PN1 and PN2 gave P* = 151 MPa for a borehole diameter of 8 mm for a = 0°(PN1 and PN2 taken from Meier et al 2013 …”

Section: Critical Borehole Breakout Initiation Pressuresmentioning

confidence: 99%

“…This fracture pattern in Posidonia Shale can be successfully modeled using the Mohr-Coulomb failure criterion (Meier et al 2013). The observed breakout depth varied along the borehole axis, possibly related to material heterogeneities such as different clay content, clastic minerals and porosity.…”

Section: Wellbore Damage In Boreholes Oriented Normal To Beddingmentioning

confidence: 99%

“…At higher loads, successive buckling failure may occur in direction normal to the bedding (Økland and Cook 1998;Blümling et al 2007;Labiouse and Vietor 2014). Under isostatic stress conditions and with bedding planes normal to the borehole axis Meier et al (2013) showed that breakouts in shales initiated without any preferred orientation. Just a few studies investigated borehole stability of shales with inclined bedding plane orientations.…”

Section: Introductionmentioning

confidence: 99%

“…Experimental studies on shale have been done mainly on samples with boreholes drilled either parallel or perpendicular to the bedding (e.g., Aoki 1993;Labiouse and Vietor 2014;Meier et al 2013). In tests on thick-walled hollow cylinders (TWHC) with bedding planes parallel to the borehole axis Labiouse and Vietor (2014) and observed that breakouts typically initiate at four positions around the borehole wall, leading to a four-lobed breakout pattern in the initial phase of loading.…”

Section: Introductionmentioning

confidence: 99%

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Influence of Bedding Angle on Borehole Stability: A Laboratory Investigation of Transverse Isotropic Oil Shale

et al. 2014

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The stability of wells drilled into bedded formations, e.g., shales, depends on the orientation between the bedding and the borehole axis. If the borehole is drilled sub-parallel to bedding, the risk of borehole instabilities increases significantly. In this study, we examined the formation of stress-induced borehole breakouts in Posidonia shale by performing a series of thick-walled hollow cylinder experiments with varying orientations of the bedding plane with respect to the borehole axis. The thickwalled hollow cylinders (40 mm in diameter and 80 mm in length containing an 8 mm diameter borehole) were loaded isostatically until formation of breakouts. The onset of borehole breakout development was determined by means of acoustic emission activity, strain measurements, ultrasonic velocities and amplitudes. The critical pressure for breakout initiation decreased from 151 MPa by approximately 65 % as the bedding plane inclination changed from normal to parallel to the borehole axis. The finely bedded structure in the shale resulted in an anisotropy in elasticity and strength from which the variation in strength dominated the integrity of the thick-walled hollow cylinders.

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Section: Critical Borehole Breakout Initiation Pressuresmentioning

confidence: 99%

Section: Wellbore Damage In Boreholes Oriented Normal To Beddingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Influence of Bedding Angle on Borehole Stability: A Laboratory Investigation of Transverse Isotropic Oil Shale

et al. 2014

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“…Calcite and quartz constitute the highest volume fractions of inclusions, with other minerals usually less than 15% [27,33,39]. In addition, there is a significant strength difference between the major inclusions (calcite/quartz) and the low volume fraction inclusions.…”

Section: Matrix-inclusion Morphologymentioning

confidence: 99%

Numerical evaluation of mean-field homogenisation methods for predicting shale elastic response

2016

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Numerical evaluation of mean-field homogenisation methods for predicting shale elastic responseReceived: date / Accepted: date Abstract Homogenisation techniques have been successfully used to estimate the mechanical response of synthetic composite materials, due to their ability to relate the macroscopic mechanical response to the material microstructure. The adoption of these mean-field techniques in geo-composites such as shales is attractive, partly because of the practical difficulties associated with the experimental characterisation of these highly heterogeneous materials. In this paper, numerical modelling has been undertaken to investigate the applicability of homogenisation methods in predicting the macroscopic, elastic response of clayey rocks. The rocks are considered as two-level composites consisting of a porous clay matrix at the first level and a matrix-inclusion morphology at the second level . The simulated microstructures ranged from a simple system of one inclusion/void embedded in a matrix to complex, random microstructures. The effectiveness and limitations of the different homogenisation schemes were demonstrated through a comparative evaluation of the macroscopic elastic response, illustrating the appropriate schemes for upscaling the microstructure of shales. Based on the numerical simulations and existing experimental observations, a randomly distributed pore system for the micro-structure of porous clay matrix has been proposed which can be used for the subsequent development and validation of shale constitutive models and their flow properties. Finally, the homogenisation techniques were used to predict the experimental measurements of elastic response. The developed methodology is proved to be a valuable too for verifying the accuracy and performance of the homogenisation techniques.

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Evolution of stress‐induced borehole breakout in inherently anisotropic rock: Insights from discrete element modeling

Kang

Kwok

2016

JGR Solid Earth

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The aim of this study is to better understand the mechanisms controlling the initiation, propagation, and ultimate pattern of borehole breakouts in shale formation when drilled parallel with and perpendicular to beddings. A two‐dimensional discrete element model is constructed to explicitly represent the microstructure of inherently anisotropic rocks by inserting a series of individual smooth joints into an assembly of bonded rigid discs. Both isotropic and anisotropic hollow square‐shaped samples are generated to represent the wellbores drilled perpendicular to and parallel with beddings at reduced scale. The isotropic model is validated by comparing the stress distribution around borehole wall and along X axis direction with analytical solutions. Effects of different factors including the particle size distribution, borehole diameter, far‐field stress anisotropy, and rock anisotropy are systematically evaluated on the stress distribution and borehole breakout propagation. Simulation results reveal that wider particle size distribution results in the local stress perturbations which cause localization of cracks. Reduction of borehole diameter significantly alters the crack failure from tensile to shear and raises the critical pressure. Rock anisotropy plays an important role on the stress state around wellbore which lead to the formation of preferred cracks under hydrostatic stress. Far‐field stress anisotropy plays a dominant role in the shape of borehole breakout when drilled perpendicular to beddings while a secondary role when drilled parallel with beddings. Results from this study can provide fundamental insights on the underlying particle‐scale mechanisms for previous findings in laboratory and field on borehole stability in anisotropic rock.

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Influence of borehole diameter on the formation of borehole breakouts in black shale

Cited by 87 publications

References 33 publications

Influence of Bedding Angle on Borehole Stability: A Laboratory Investigation of Transverse Isotropic Oil Shale

Influence of Bedding Angle on Borehole Stability: A Laboratory Investigation of Transverse Isotropic Oil Shale

Numerical evaluation of mean-field homogenisation methods for predicting shale elastic response

Evolution of stress‐induced borehole breakout in inherently anisotropic rock: Insights from discrete element modeling

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