Strength anisotropies in mudrocks

Ajalloeian, Rassoul; Lashkaripour, Gholam Reza

doi:10.1007/s100640000055

Cited by 75 publications

(15 citation statements)

References 4 publications

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“…The output of the model is the moisture content, which is an important parameter to update the UCS (uniaxial compressive strength) of the rock. It is shown that increase in the moisture content of shale has a negative effect on its compressive strength, as noted by various investigators [21,[43][44][45][46]. The presented correlations share a common theme in which uniaxial compressive strength reduces exponentially as the moisture content increases (Table 2).…”

Section: Resultssupporting

confidence: 53%

Effects of Sorptive Tendency of Shale on Borehole Stability

Dokhani¹,

Yu²

2016

JGRE

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Abstract:Interactions between aqueous drilling fluids and clay minerals have been identified as an important factor in wellbore instability of shale formations. Current wellbore stability models consider the interactions between aqueous drilling fluids and pore fluid but the interactions with shale matrix are neglected. This study provides a realistic method to incorporate the interaction mechanism into wellbore stability analysis through laboratory experiment and mathematical modeling. The adsorption isotherms of two shale rocks, Catoosa Shale and Mancos Shale are obtained. The adsorption isotherms of the selected shales are compared with those of other shale types in the literature. This study shows that the adsorption theory can be used to generalize wellbore stability problem in order to consider the case of non-ideal drilling fluids. Furthermore, the adsorption model can be combined with empirical correlations to update the compressive strength of shale under downhole conditions. Accordingly, a chemo-poro-elastic wellbore stability simulator is developed to explore the stability of transversely isotropic shale formations. The coupled transport equations are solved using an implicit finite difference method. The results of this study indicate that the range of safe mud weight reduces due to the moisture adsorption phenomenon.

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Section: Resultssupporting

confidence: 53%

Effects of Sorptive Tendency of Shale on Borehole Stability

Dokhani¹,

Yu²

2016

JGRE

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“…Niandou et al, 1997;Val es et al, 2004), others do show slight to significant strengthening parallel to bedding (e.g. Fjaer and Nes, 2014;Ajalloeian and Lashkaripour, 2000). All results given in this paper are for compaction and deformation normal to bedding and should not be extended to other stress orientations with respect to fabric anisotropies.…”

Section: Discussionmentioning

confidence: 85%

“…However, static rock strength decreases from orientations normal to bedding through to 30e45 to bedding, then increases again as the maximum principal stress becomes parallel to bedding, sometimes exceeding the bedding normal strength, sometimes equalling it (e.g. Fjaer and Nes, 2014;Niandou et al, 1997;Ajalloeian and Lashkaripour, 2000). Hence, trying to estimate shale strength from velocity in a deviated well would be significantly flawed (Sayers et al, 2009).…”

Section: Discussionmentioning

confidence: 94%

Empirical strength prediction for preserved shales

Dewhurst

Sarout

Piane

et al. 2015

Marine and Petroleum Geology

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“…Although this assumption is considered satisfactory for modeling stability of isotropic rocks, it is not valid while drilling through high angle wells (sub-parallel to bedding) through laminated (anisotropic) shale because the bedding layers serve as weak planes that result in strength anisotropy [39][40][41][42][43][44][45][46][47][48][49] . Chenevert (1965) studied the mechanical anisotropies of laminated sedimentary rocks experimentally 39 and determined that the formation compressive strength can vary significantly as the angle between the direction of the axial load and bedding planes vary.…”

Section: Wellbore Stability Modelingmentioning

confidence: 99%

Wellbore Stability Considerations for Drilling High-Angle Wells Through Finely Laminated Shale: A Case Study From Terra Nova

Gallant

Zhang²,

Wolfe

et al. 2007

Proceedings of SPE Annual Technical Conference and Exhibition

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fax 01-972-952-9435. AbstractHigh angle wells drilled into finely laminated shale are often found to be less stable than comparable wells drilled into nonlaminated rock. This can be attributed to a variety of factors including, but not limited to, well trajectory, the in-situ stress field, rock strength anisotropy, shale reactivity issues, chemical imbalances between the drilling fluid and shale pore fluid, and many others. However, due to the lack of available data some of these mechanisms are difficult to quantify and therefore are typically not accounted for during well planning. This can result in significant wellbore instability issues that substantially elevate drilling operation costs.In this paper, a comprehensive approach to account for many of these wellbore instability mechanisms is outlined. A plane-of-weakness model is utilized to account for the effects of weak bedding planes and other discontinuities. The model uses parameters that are obtained by curve fitting triaxial strength test results conducted at various angles with respect to bedding. Additionally, traditional mechanical and chemical effects were also addressed and incorporated into the pre-drill model to assist in well planning. The model was then implemented at the Terra Nova field for the case of a highly deviated wellbore drilled through finely laminated shale nearly parallel to bedding.Real-time monitoring of measurement and logging while drilling data was key to identifying the unstable sections so that the root cause of instability could be diagnosed. The appropriate remedial action was then applied and wellbore instability problems were mitigated.Both mechanical and chemical borehole instability models were applied in a case history to evaluate the potential for wellbore instability. In particular, bedding-plane related and chemically-induced instability were addressed and overcome through comprehensive modeling and the deployment of modified operational procedures.

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Strength anisotropies in mudrocks

Cited by 75 publications

References 4 publications

Effects of Sorptive Tendency of Shale on Borehole Stability

Effects of Sorptive Tendency of Shale on Borehole Stability

Empirical strength prediction for preserved shales

Wellbore Stability Considerations for Drilling High-Angle Wells Through Finely Laminated Shale: A Case Study From Terra Nova

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