Abstract

Predicting the nature and extent of deformation adjacent to wellbores can be critical for successful subsurface operations. The ability to capture the onset and evolution of failure can permit more efficient operations and circumvent or minimize the effects of well-known operational issues such as wellbore instability and sand production. In this paper, the behaviour of porous sandstones is investigated through replication of experimental testing conducted by Haimson (2004). In this work the deformation near the excavated section for highly porous sandstones was documented and analyzed, with contrasting deformational styles observed that are tentatively attributed to mineral composition. The requirements for predicting these styles are discussed and presented within a novel three-field modelling framework that incorporates a sophisticated constitutive model. Application of the workflow and results for breakout and sand control studies is discussed, along with potential future extensions to the capabilities of the constitutive model.

Introduction

Instability of subsurface excavations is critical and can pose serious problems affecting the timing and success of a project. Prediction of such instabilities has long been recognised as a key factor in many industries. Understanding the failure mechanisms is vital for the optimisation of well production as instabilities affect drilling efficiency, resulting in lost circulation, breakouts, or hole closure and even in loss of the open-hole section due to stuck and damaged drill pipe (Lang et al., 2011). Nevertheless, such instabilities are useful for informing on stress directions and magnitudes (Haimson and Song, 1993). Borehole logging has been long used to estimate stress directions, based on the location of the breakouts around the well (Brudy et al., 1997; Zoback et al, 2003; Kingdon et al., 2016). In addition, several studies have suggested that the characteristics and dimensions of the breakouts, if properly measured, can also inform on the magnitudes of far-field stresses.

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