Application of a Modified Strain Rate Dependent Constitutive Model for Well-Bore Stability Analyses in Chalk Reservoirs

This paper utilises a recently modified 3D geo-mechanical constitutive model for wellbore stability analyses. The modified constitutive model using two independent yield surfaces composed of shear failure and a strain rate-dependent pore collapse yield surfaces in order to describe dilation and compaction mechanism of deformation was developed based on the combination of non-associated shear failure and an associated viscoelastic consistency model relying on empirical formulation originally developed by J.A. de Waal and co-workers in the late 1980s. A fully implicit stress-update algorithm for multi-mechanism consistency model is used to determine the viscoplastic strain components. In this study, a series of single lateral hole (SLH) experiments were conducted on chalk samples. For this purpose, a horizontal wellbore was drilled laterally at the center of the specimen and loaded under triaxial condition with constant stress ratio. The SLH samples were scanned after the experiments using Computed Tomography scanning to precisely identify the damaged zones formed around the borehole. The results from the experiments and CT analysis were compared with the model prediction and a good agreement was observed.