Effect of anisotropic borehole wall failures when estimating in situ stresses: A case study in the Nankai accretionary wedge

The postearthquake stress state on the Tohoku megathrust as constrained by reanalysis of the JFAST breakout data

“…Note that in steeply dipping strata with strong strength anisotropy, rotation of breakout azimuth away from true stress directions to align with bedding strike can occur if the dip directions of strata are not aligned with S Hmax [Lee et al, 2013]. The azimuth of the preferred solution is rotated 28°clockwise from the convergence direction.…”

“…Following Zoback [2007], we calculate the stress concentration on the borehole wall using the Kirsch equations for horizontal stress states [Jaeger and Cook, 1976]. This formulation presumes that upon borehole excavation, the surrounding rocks behave dominantly elastically; this is likely to be valid because even for shallowly buried sediments that undergo plastic yield during burial, the unloading associated with opening of the borehole should result in elastic behavior.…”

A wellbore stability analysis model with chemical-mechanical coupling for shale gas reservoirs

“…Despite these efforts to modify the wellbore stability models, numerous accidents associated with wellbore instability in shale gas reservoirs have been reported (Yan et al, 2013Ma and Chen, 2014a,b,c). Zoback (2012) and Lee et al (2012Lee et al ( , 2013 found that the shapes and orientations of failure regions are significantly affected by anisotropic strength, and a few researchers have also studied the influence of anisotropic strength on instability regions around the borehole (Lee et al, 2012(Lee et al, , 2013Ma and Chen, 2014b). In addition, a few researchers have investigated the influence of multiple weak planes Chen et al, 2014a).…”

Effect of material anisotropy on time-dependent wellbore stability

“…Matrix failure coupled with slip failure effect on optimum drilling mud weight for inclined boreholes is discussed in literature, 10,11 but isotropic stress models are used and no timedependent analysis is discussed. Observed anisotropic shear failure around the borehole caused by matrix and slip failures and their effect on estimating in-situ stresses is analyzed by Lee et al 12 However, the authors do not consider anisotropy in mechanical properties, and a homogenous isotropic rock is assumed throughout. Yan et al 13 address this shortcoming by analyzing borehole stability using an anisotropic linear elasticity model while accounting for rock strength anisotropy, but fall short to account for the time-dependent poroelastic effect.…”